TABLE OF CONTENTS
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1. SURFACE ANATOMY OF THE ANTERIOR ABDOMINAL WALL
2. OSTEOLOGY OF THE ANTERIOR ABDOMINAL WALL
3. LEARNING OBJECTIVES – ANTERIOR ABDOMINAL WALL / INGUINAL REGION
4. MONDAY, JANUARY 4 – DISSECTION OF THE ANTERIOR ABDOMINAL WALL
6. FOCUS QUESTIONS – ANTERIOR ABDOMINAL WALL AND INGUINAL REGION
7. LEARNING OBJECTIVES – PERITONEUM AND PERITONEAL CAVITY
8. WEDNESDAY, JANUARY 6 – OVERVIEW OF THE ABDOMINAL VISCERA AND PERITONEUM
9. FRIDAY, JANUARY 8 -Celiac Trunk, Stomach, Spleen, Liver, and Gallbladder
11. TUESDAY, JANUARY 12 –Duodenum and pancreas / Removal of the Gastrointestinal Tract
13. FOCUS QUESTIONS FOR PERITONEUM AND PERITONEAL CAVITY
14. FRIDAY, JANUARY 15 – POSTERIOR ABDOMINAL REGION / DIAPHRAGM
15. FOCUS QUESTIONS FOR POSTERIOR ABDOMINAL REGION
The abdomen is the portion of the trunk that lies between the thorax and the pelvis. The abdominal cavity is divided from the thoracic cavity by the diaphragm but it is continuous with the pelvic cavity. Viscera contained within the abdominal cavity are not bilaterally symmetrical. Therefore, it is worth noting that use of the words “right” and “left” in names and instructions refers to the right and left sides of the cadaver in the anatomical position.
Surface anatomy will be studied on a living subject as part of your assigned SURFACE ANATOMY EXERCISES.
Surface Anatomy
Firm fixation of tissues in the cadaver may make it difficult to distinguish between bony landmarks and well-fixed soft tissue structures. However, before beginning your dissection, you should make an effort to plapate, or at least appreciate the general location of specific anatomic landmarks. Place the cadaver in the supine position and attempt to palpate the following structures (Figure 4.1):
Use a skeleton to identify the following structures (Figure 4.2):
ANTERIOR ABDOMINAL WALL / INGUINAL CANAL / TESTES AND SCROTUM
LEARNING OBJECTIVES: Upon completion of this session, the student will be able to:
MONDAY, JANUARY 4 -Superficial Fascia of the Anterolateral Abdominal Wall
Dissection Overview
The contents of the abdominal cavity are protected by the anterolateral abdominal wall. The organization of the layers forming the anterolateral abdominal wall is illustrated in Figure 4.4. The superficial fascia is unique in this region in that it has a superficial fatty layer called Camper's fascia and a deep membranous layer called Scarpa's fascia. The membranous layer is noteworthy, because it is continuous with named fasciae in the perineum.
Dissection Instructions
Skin Incisions
Superficial Fascia
1. Use a probe to tear through the superficial fascia about 7.5 cm lateral to the midline (Figure 4.6). The superficial epigastric artery and vein are in the superficial fascia in this area, but do not make a special effort to find them.
2. Dissect through the superficial fascia down to the aponeurosis of the external oblique muscle. On the medial side of the incision, place your fingers deep to the superficial fascia and separate the superficial fascia from the aponeurosis of the external oblique muscle (Figure 4.6, arrow 1). As you remove the superficial fascia, observe that its deep surface is fibrous connective tissue containing relatively little fat (Scarpa's fascia) and the more superficial part is composed entirely of fat (Camper's fascia).
3. As you approach the midline, palpate the anterior cutaneous nerves that enter the superficial fascia about 2 to 3 cm lateral to the midline. Clean one anterior cutaneous nerve. The abdominal anterior cutaneous nerves are branches of intercostal nerves (T7 to T11), the subcostal nerve (T12), and the iliohypogastric and ilioinguinal nerves (L1). Consult a dermatome chart and note that:
o T7 innervates the skin overlying the tip of the xiphoid process.
o T10 innervates the skin of the umbilicus.
o T12 innervates the skin superior to the pubic symphysis.
o L1 innervates the skin overlying the pubic symphysis.
4. Lateral to the incision, use your fingers to separate the superficial fascia from the external oblique muscle (Figure 4.6, arrow 2). As you near the midaxillary line, palpate the lateral cutaneous nerves entering the superficial fascia. The lateral cutaneous nerves are branches of intercostal nerves or the subcostal nerve. Clean the branches of one lateral cutaneous nerve.
5. Remove the superficial fascia in an inferior direction until the lower border of the external oblique muscle is exposed (approximately 2.5 cm into the proximal thigh).
Dissection Review
IN THE CLINIC:Superficial Veins of the Abdominal Wall
The superficial epigastric vein anastomoses with the lateral thoracic vein in the superficial fascia. This is an important collateral venous channel from the femoral vein to the axillary vein. In patients who have an obstruction of the inferior vena cava or hepatic portal vein, the superficial veins of the abdominal wall may be engorged, and may become visible around the umbilicus (caput medusae).
Muscles of the Anterolateral Abdominal Wall
Dissection Overview
Three flat muscles (external oblique, internal oblique, and transversus abdominis) form most of the anterolateral abdominal wall. The rectus abdominis muscle completes the anterior abdominal wall near the midline. The three flat muscles have fleshy proximal attachments (to the ribs, vertebrae, and pelvis) and broad, aponeurotic distal attachments (to the ribs, linea alba, and pubis). Each of the three flat muscles contributes to the formation of the rectus sheath and the inguinal canal.
In the male, the testes are housed in the scrotum, which is an outpouching of the anterior abdominal wall. Each testis passes through the abdominal wall during development, dragging its ductus deferens behind it. This passage occurs through the inguinal canal. The inguinal canal is located superior to the medial half of the inguinal ligament and extends from the superficial (external) inguinal ring to the deep (internal) inguinal ring. In the female, the inguinal canal is smaller in diameter.
It must be noted that the structures forming the inguinal canal are identical in the two sexes, but the contents of the inguinal canal differ. In the male, the inguinal canal contains the spermatic cord, while in the female the inguinal canal contains the round ligament of the uterus. Dissection instructions are provided for male cadavers, but these instructions are applicable to female cadavers.
The order of dissection will be as follows: The three flat muscles of the abdominal wall will be studied, particularly in the inguinal region. The composition and contents of the rectus sheath will be explored. The anterior abdominal wall will be reflected.
Dissection Instructions
External Oblique Muscle
Internal Oblique Muscle
The internal oblique muscle lies deep to the external oblique muscle. The internal oblique muscle forms the intermediate layer of the inguinal canal (Figure 4.8B). To expose the internal oblique muscle, the external oblique muscle must be transected and reflected (Figure 4.9). Perform this transection bilaterally.
1. In the midaxillary line at the level of the umbilicus insert closed scissors between the fibers of the external oblique muscle. Open the scissors parallel to the muscle fiber direction to create an opening in the external oblique muscle. Insert your finger into the opening and direct it inferiorly to create space between the external oblique muscle and the underlying internal oblique muscle. Then use scissors to make a vertical cut to the ASIS. (Figure 4.9, left-side, cut 1).
2. Insert your fingers into cut 1 and use blunt dissection to separate the fibers of the external oblique muscle from the underlying internal oblique muscle. Note that your fingers cannot pass medial to the semilunar line because the external oblique aponeurosis is fused to the internal oblique aponeurosis.
3. In the transumbilical plane, use scissors to cut the external oblique muscle. Extend the cut as far medially as the semilunar line (Figure 4.9, left-side, cut 2).
4. Inferior to cut 2, use your fingers to separate the external oblique muscle from the internal oblique muscle. Be gentle as you approach the superficial inguinal ring.
5. Using scissors, make an incision from the medial end of cut 2 to a point 2.5 cm from the superior margin of the superficial inguinal ring (Figure 4.9, left-side, cut 3). DO NOT CUT THROUGH THE INTERCRURAL FIBERS (APEX) OF THE SUPERCIAL INGUINAL RING. Cut 3 should follow the lateral side of the semilunar line and cut only the external oblique aponeurosis.
6. Reflect the external oblique muscle in an inferior and lateral direction to reveal the lower half of the internal oblique muscle (Figure 4.9, right-side).
7. Identify the internal oblique muscle. The proximal attachments of the internal oblique muscle are the thoracolumbar fascia, the iliac crest, and the lateral half of the inguinal ligament. The distal attachments of the internal oblique muscle are the inferior borders of ribs 10 to 12, the linea alba, the pubic crest, and the pecten pubis.
8. Observe the portion of the internal oblique muscle that arises from the lateral part of the inguinal ligament (Figure 4.10). Note that this portion of the internal oblique muscle arches medially and attaches to the pecten pubis. It contributes to the roof of the inguinal canal.
9. Lateral to the spermatic cord (or round ligament of the uterus), observe muscle fibers connecting the internal oblique muscle to the spermatic cord (or round ligament) (Figure 4.10). This is the layer of cremaster muscle and fascia, which is the contribution of the internal oblique muscle to the coverings of the spermatic cord in the male. In the female, the cremaster muscle and fascia surround the round ligament of the uterus.
10. In the intermuscular plane between the external oblique and the internal oblique muscles, look for two nerves (Figure 4.8B):
o Ilioinguinal nerve courses through the inguinal canal to emerge at the superficial inguinal ring.
o Iliohypogastric nerve runs parallel to the ilioinguinal nerve and superior to it, outside of the inguinal canal.
11. Just medial to the superficial inguinal ring, the aponeurosis of the internal oblique becomes fused with the aponeurosis of the transversus abdominis muscle to form the conjoint tendon (Figure 4.10).
Transversus Abdominis Muscle The transversus abdominis muscle lies deep to the internal oblique muscle. The transversus abdominis muscle contributes to the deepest layer of the inguinal canal (Figure 4.8C). In the inguinal region the transversus abdominis muscle has attachments and fiber directions that are similar to the internal oblique muscle.
Use an illustration to study the proximal attachments, distal attachments, and fiber direction of the transversus abdominis muscle. The proximal attachments of the transversus abdominis muscle are the internal surfaces of the costal cartilages of ribs 7 to 12, the thoracolumbar fascia, the iliac crest, and the lateral third of the inguinal ligament. The distal attachments of the transversus abdominis muscle are the linea alba, the pubic crest, and the pecten pubis.
Dissection Note: The transversus abdominis muscle is often difficult to separate from the internal oblique muscle because their tendons are fused near their distal attachments (conjoint tendon), and the muscle bellies adhere to each other laterally. You do not have to separate the internal oblique muscle from the transverses abdominis muscle.
Deep Inguinal Ring
Transversalis fascia lines the inner surface of the abdominal muscles (Figure 4.4). The deep inguinal ring is the point at which the testis passed through the transversalis fascia during development. The deep inguinal ring is located superior to the midpoint of the inguinal ligament and it marks the deep extent of the inguinal canal. In the male, the ductus deferens passes through the deep inguinal ring. In the female, the round ligament of the uterus passes through the deep inguinal ring.
IN THE CLINIC: Inguinal Hernias
The inguinal canal is a weak area of the abdominal wall through which abdominal viscera may protrude (inguinal hernia). An inguinal hernia is classified according to its position relative to the inferior epigastric vessels (Figure 4.11A). An indirect inguinal hernia exits the abdominal cavity through the deep inguinal ring lateral to the inferior epigastric vessels, and it follows the inguinal canal (an indirect course through the abdominal wall) (Figure 4.11B). In contrast, a direct inguinal hernia exits the abdominal cavity medial to the inferior epigastric vessels and it follows a direct course through the abdominal wall (Figure 4.11C).
Rectus Abdominis Muscle
The rectus sheath is formed by the aponeuroses of the three flat abdominal muscles. The rectus sheath contains the rectus abdominis muscle, the superior and inferior epigastric vessels, the terminal ends of the ventral rami of spinal nerves T7 to T12, and the pyramidalis muscle.
IN THE CLINIC: Epigastric Anastomoses
The superior epigastric vessels anastomose with the inferior epigastric vessels within the rectus sheath (Figure 4.14). If the inferior vena cava becomes obstructed, the anastomosis between the inferior epigastric and superior epigastric veins provides a collateral venous channel that drains into the superior vena cava. If the aorta is occluded, collateral arterial circulation to the lower part of the body occurs through the superior and inferior epigastric arteries.
Dissection Review
TUESDAY, JANUARY 5 -Dissection of the Scrotum, Spermatic Cord and Testis / Reflection of the Anterior Abdominal Wall
The scrotum is an outpouching of the anterior abdominal wall, and most layers of the abdominal wall are represented in its structure (Figure 5.7). The superficial fascia of the scrotum contains no fat. Instead, the superficial fascia is represented by dartos fascia, which contains smooth muscle fibers (dartos muscle).
The order of dissection will be as follows: The scrotum will be opened by a vertical incision along its anterior surface. The spermatic cord will be followed from the superficial inguinal ring into the scrotum. The testis will be removed from the scrotum. The spermatic cord will be dissected. The testis will be studied.
Scrotum Dissection Instructions
Spermatic Cord
The spermatic cord contains the ductus deferens, testicular vessels, lymphatics, and nerves. The contents of the spermatic cord are surrounded by three fascial layers, the coverings of the spermatic cord, which are derived from layers of the anterior abdominal wall (Figure 5.7). These coverings are added to the spermatic cord as it passes through the inguinal canal.
IN THE CLINIC: Vasectomy
The ductus deferens can be surgically interrupted in the superior part of the scrotum (vasectomy). Sperm production in the testis continues but the spermatozoa cannot reach the urethra.
Testis
The testis is covered by the tunica vaginalis, a serous sac that is derived from the parietal peritoneum (Figure 5.7). The tunica vaginalis has a visceral layer and a parietal layer (Figure 5.9). The cavity of the tunica vaginalis is only a potential space that contains a very small amount of serous fluid.
IN THE CLINIC: Lymphatic Drainage of the Testis
Lymphatics from the scrotum drain to the superficial inguinal lymph nodes. Inflammation of the scrotum may cause tender, enlarged superficial inguinal lymph nodes. In contrast, lymphatics from the testis follow the testicular vessels through the inguinal canal and into the abdominal cavity where they drain into lumbar (lateral aortic) nodes and preaortic lymph nodes. Testicular tumors may metastasize to lumbar and preaortic lymph nodes, not to superficial inguinal lymph nodes.
Dissection Review
Reflection of the Abdominal Wall
Dissection Overview
The anterior abdominal wall will be reflected in such a way that the contents of the abdominopelvic cavity can be accessed, but the abdominal wall can be repositioned for review. The incision lines will be similar to the quadrant lines. The incisions are designed to give direct reference to the position of the abdominal organs within the abdominal quadrants.
The order of dissection will be as follows: The anterior abdominal wall will be incised and opened. The inner surface of the anterior abdominal wall will be studied.
Dissection Instructions
1. Name and define the nine regions of the anterior abdominal wall, list the importance of each.
2. In the thigh there are lymph nodes below the plane of the inguinal ligament. What regions do they drain?
3. Distinguish between the fatty layer and the membranous layer of the subcutaneous tissue.
4. What is the extent of the membranous layer of the subcutaneous tissue?
5. What are the characteristics of the subcutaneous tissue that continues into the scrotum as the dartos tunic?
6. Locate exemplary anterior and lateral cutaneous branches of one of the segmental nerves to the abdominal wall. What is their source? Which segmental nerves supply the abdominal wall? Do they run horizontally or follow the slope of the ribs?
7. Define the superficial inguinal ring and locate it on the anterior abdominal wall using anatomical landmarks.
8. Consider the sources and extent of distribution of the ilioinguinal nerve.
9. What does the superficial inguinal ring transmit in the female? In the male?
10. How do you differentiate the external abdominal oblique from the internal abdominal oblique?
11. Where do the iliohypogastric and ilioinguinal nerves pierce the internal and external abdominal oblique muscles? To where do they distribute?
12. Where does the cremaster muscle lie in relation to the external spermatic fascia?
13. Find the segmental vessels and nerves on the surface of the transversus abdominis muscle and consider their level, origin, areas of distribution, oblique orientation, and the manner in which they enter the rectus sheath.
14. Locate superior and inferior epigastric arteries. What are their sources? Do they anastomose?
15. At what level (relative to the umbilicus) do you find the arcuate line? Is it distinct?
16. What tissue is left on the posterior side of the rectus muscle caudal to this line?
17. Review the descent of the gonads.
18. What does the small genital branch of the genitofemoral nerve innervate?
19. What tissue forms the deep (internal) inguinal ring, and how does it do so?
20. What passes through the deep ring?
21. What are the relationships of the medial inguinal fossa and lateral inguinal fossa to the weak fascia and the deep inguinal ring?
22. Define the inguinal triangle.
23. What is the relationship between direct and indirect inguinal hernias and the falx inguinalis, weak fascia, deep and superficial inguinal rings, inguinal canal, and inguinal ligament?
24. How are the coverings of the spermatic cord represented in the scrotum?
25. Compare the inguinal canal in male and female:
26. To what does the round ligament of the uterus attach?
27. What is its male homologue?
28. What is the scrotal ligament?
Peritoneum and Peritoneal Cavity
Upon completion of this session, the student will be able to:
WEDNESDAY, JANUARY 6 – OVERVIEW OF THE ABDOMINAL VISCERA AND PERITONEUM
Dissection Overview
All body cavities (thoracic cavity, pericardial cavity, and abdominopelvic cavity) are lined by serous membranes, which secrete a small amount of fluid to lubricate the movements of organs. In the abdominal cavity and pelvic cavity this membrane is called the peritoneum. There are two types of peritoneum: Parietal peritoneum lines the inner surfaces of the abdominal and pelvic walls, and visceral peritoneum covers the surfaces of the abdominal and pelvic organs. Between these two types of peritoneum is a potential space called the peritoneal cavity.
During development, some organs develop in the peritoneal cavity and are called intraperitoneal (peritoneal) organs. Examples of intraperitoneal organs include the stomach, small intestine, liver, and spleen. Some organs develop behind the peritoneum and are called retroperitoneal (extraperitoneal) organs: The ureters, suprarenal glands, and kidneys are examples. Some parts of the gastrointestinal tract begin as intraperitoneal organs and then become attached to the abdominal wall during development. These organs are secondarily retroperitoneal. Examples of secondarily retroperitoneal organs include the duodenum, pancreas, ascending colon, and descending colon.
The order of dissection will be as follows: The abdominal viscera will be identified and localized by abdominal quadrant. The named specializations of the peritoneum will be studied. For a more complete understanding, review the development of the gastrointestinal tract before examining the peritoneal specializations.
Dissection Instructions
Abdominal Viscera
1. Use your hands to inspect the abdominal cavity. As you perform the inspection, you may encounter adhesions. If adhesions are present, tear them with your fingers to mobilize the organs.
2. Open the flaps of the abdominal wall. The incision lines correlate to the abdominal quadrant lines. As you examine the organs, you should close and open the flaps to help you relate the organs to the abdominal quadrants. Most of the organs to be identified are parts of the gastrointestinal tract.
3. Identify the liver (Figure 4.17). It is an intraperitoneal organ. The liver occupies the right upper quadrant and extends across the midline into the left upper quadrant. The liver lies against the inferior surface of the diaphragm. The attachment of the falciform ligament divides the liver into right and left anatomical lobes.
4. The gallbladder (Figure 4.17), an intraperitoneal organ, is also in the right upper quadrant. The gallbladder extends below the inferior border of the liver. It is usually found at the tip of the right ninth costal cartilage in the midclavicular line. Confirm this relationship.
5. Identify the stomach (Figure 4.17). It is an intraperitoneal organ and lies in the left upper quadrant. It is continuous with the esophagus proximally and the duodenum distally. The liver partially covers the anterior surface of the stomach.
6. Find the spleen. It is an intraperitoneal organ that lies in the left upper quadrant. It is found posterior to the stomach and may be difficult to find unless it is enlarged. Reach around the left side of the stomach with your right hand and palpate the spleen.
7. Identify the greater omentum (Figure 4.17). The greater omentum is attached to the greater curvature of the stomach (Figure 4.22). Reflect the greater omentum superiorly over the costal margin (Figure 4.18).
8. Identify the small intestine (Figures 4.18 and 4.19). The small intestine begins at the pyloric end of the stomach. It has three parts:
o Duodenum
o Jejunum
o Ileum
9. Most of the duodenum is secondarily retroperitoneal. It will be studied with the pancreas.
10. The jejunum and ileum are intraperitoneal organs that extend from the left upper quadrant to the right lower quadrant, but due to their length and mobility, they occupy all four quadrants. Beginning in the left upper quadrant, pass the jejunum and ileum between your hands and appreciate their length, position, and termination.
11. Identify the large intestine. The large intestine begins in the right lower quadrant at the ileocecal junction (Figure 4.19). It has six parts:
o Cecum – located in the right lower quadrant. The appendix is attached to the inferior end of the cecum.
o Ascending colon extends from the right lower quadrant to the right upper quadrant. It ends at the right colic (hepatic) flexure. The ascending colon is secondarily retroperitoneal.
o Transverse colon extends from the right upper quadrant to the left upper quadrant. The transverse colon ends at the left colic (splenic) flexure. The transverse colon is intraperitoneal.
o Descending colon extends from the left upper quadrant to the left lower quadrant. The descending colon is secondarily retroperitoneal.
o Sigmoid colon – located in the left lower quadrant. The sigmoid colon ends in the pelvic cavity at the level of the third sacral vertebral level. The sigmoid colon is an intraperitoneal organ.
o Rectum – located in the pelvic cavity. The rectum will be dissected with the pelvic viscera.
12. Use your hands to trace the large intestine from the right lower quadrant to the left lower quadrant. Note the position (quadrant) and mobility of each of its parts.
Peritoneum
1. Observe the visceral peritoneum on the surface of the stomach or small intestine (Figure 4.20). Note that visceral peritoneum is smooth and slippery.
2. Observe the parietal peritoneum on the inner surface of the abdominal wall (Figure 4.20). Note that parietal peritoneum is also smooth and slippery.
3. Observe the greater omentum (Figure 4.17). Spread this apron-like structure to appreciate its size. The greater omentum normally lies between the intestines and the anterior abdominal wall (Figure 4.20).
4. Elevate the inferior border of the liver and identify the lesser omentum (Figure 4.20). The lesser omentum passes from the lesser curvature of the stomach and first part of the duodenum (Figure 4.22) to the inferior surface of the liver. The lesser omentum has two parts:
o Hepatogastric ligament extends from the liver to the lesser curvature of the stomach.
o Hepatoduodenal ligament extends from the liver to the first part of the duodenum.
5. Return the right upper quadrant flap to its anatomical position and review the falciform ligament. The falciform ligament passes from the parietal peritoneum on the anterior abdominal wall to the visceral peritoneum on the surface of the liver. The round ligament of the liver (ligamentum teres hepatis) is the obliterated umbilical vein, and it is found in the inferior free margin of the falciform ligament.
6. Follow the falciform ligament superiorly and observe that it is one part of the coronary ligament that attaches the liver to the diaphragm. Two additional peritoneal ligaments are also parts of the coronary ligament:
o Left triangular ligament – located between the left lobe of the liver and the diaphragm
o Right triangular ligament – located between the right lobe of the liver and the diaphragm
7. The gastrophrenic ligament connects the superior part of the greater curvature of the stomach to the diaphragm. Slide your hand superiorly to the left of the stomach to feel this ligament.
8. The gastrosplenic (gastrolienal) ligament passes from the greater curvature of the stomach to the spleen, and the splenorenal (lienorenal) ligament connects the spleen to the posterior abdominal wall over the left kidney (Figure 4.21).
9. Reflect the greater omentum superiorly over the costal margin and identify the transverse mesocolon (Figures 4.18 and 4.20). The transverse mesocolon attaches the transverse colon to the posterior abdominal wall. At the left end of the transverse mesocolon is the phrenicocolic ligament (Figure 4.28), which attaches the left colic flexure to the diaphragm.
10. Identify the mesentery (Figure 4.20). The mesentery suspends the jejunum and ileum from the posterior abdominal wall. The root of the mesentery attaches to the posterior abdominal wall from the left upper quadrant to the right lower quadrant.
11. Observe the mesoappendix (Figure 4.33). The mesoappendix attaches the appendix to the posterior abdominal wall and it contains the appendicular artery.
12. Identify the sigmoid mesocolon in the lower left quadrant (Figure 4.35). The sigmoid mesocolon suspends the sigmoid colon from the posterior abdominal wall.
13. Note that these peritoneal structures are all related to a subdivision of the peritoneal cavity called the greater peritoneal sac (Figure 4.20). Posterior to the stomach and lesser omentum is a smaller subdivision of the peritoneal cavity called the lesser peritoneal sac (omental bursa) (Figures 4.20 and 4.21).
14. The omental foramen (epiploic foramen) connects the greater and lesser peritoneal sacs. The omental foramen lies posterior to the hepatoduodenal ligament (Figure 4.21).
15. Insert your finger into the omental foramen and review its four boundaries:
o Anterior – hepatic portal vein, hepatic artery proper, and bile duct contained within the hepatoduodenal ligament (Figure 4.21)
o Posterior – inferior vena cava and right crus of the diaphragm covered with parietal peritoneum
o Superior – caudate lobe of the liver covered with visceral peritoneum
o Inferior – first part of the duodenum covered with visceral peritoneum
16. Study a diagram of the lesser peritoneal sac (Figure 4.20). The lowest part of the lesser peritoneal sac is called the inferior recess and it extends inferiorly as far as the greater omentum. During development, the inferior recess extended between the layers of the greater omentum (review an embryology text). The highest part of the lesser peritoneal sac is the superior recess. The diaphragm lies posterior to the superior recess and the caudate lobe of the liver is anterior to the superior recess.
17. Posterior to the main part of the lesser peritoneal sac is the pancreas (Figure 4.20). The peritoneum that covers the pancreas forms part of the posterior wall of the lesser peritoneal sac.
Dissection Review
1. Use the cadaver specimen to review all parts of the gastrointestinal tract in proximal to distal order. State the quadrant(s) in which each abdominal organ normally is found.
2. Review all parts and specializations of the peritoneum listed on the preceding pages.
3. Review the embryology of the gut tube and mesenteries.
FRIDAY, JANUARY 8 -Celiac Trunk, Stomach, Spleen, Liver, and Gallbladder
Dissection Overview
The order of dissection will be as follows: The ribs and diaphragm will be cut to allow the liver to be retracted superiorly, exposing the lesser omentum. The surface features of the stomach will be studied. The vessels and ducts in the hepatoduodenal ligament will be demonstrated. The branches of the celiac trunk that supply the stomach, spleen, liver, and gallbladder will be dissected. The remainder of the field of supply of the celiac trunk (to the duodenum and pancreas) will be dissected later. The hepatic portal vein will be studied. The spleen, liver, and gallbladder will be studied.
Dissection Instructions
1. Place the greater omentum in its correct anatomical position (Figure 4.17).
2. Identify the parts of the stomach (Figure 4.22):
o Anterior surface
o Greater curvature
o Cardia
o Cardial notch
o Fundus
o Body
o Angular incisure (notch)
o Pyloric part
o Pylorus
3. Identify the following features of the liver (Figure 4.23A,B):
o Right anatomical lobe
o Left anatomical lobe
o Diaphragmatic surface
o Inferior border
4. Use your hand to raise the inferior border of the liver. Identify the visceral surface of the liver (Figure 4.23). The visceral surface is in contact with the gallbladder and the peritoneum covering the stomach, duodenum, colon, right kidney, and right suprarenal gland.
5. Identify the porta hepatis on the visceral surface of the liver. It is the fissure through which vessels, ducts, lymphatics, and nerves enter the liver (Figure 4.23B).
6. Identify the gallbladder (Figure 4.23B). The gallbladder may have been surgically removed.
Celiac Trunk
As you dissect the branches of the celiac trunk, realize that arteries are named by their region of distribution, not by their origin or branching pattern.
1. Use bone cutters to detach the costal cartilages of ribs 6 and 7 from the xiphisternal junction and lateral border of the sternum. Working through the opening just created, use scissors to make a vertical cut through the diaphragm. Extend this cut to the coronary ligament on the superior surface of the liver. Retract the ribs, diaphragm, and liver superiorly to expose the lesser omentum. If necessary, place one hand in the right costodiaphragmatic recess to elevate the costal margin and use scissors to detach the diaphragm from its costal attachments.
2. Insert the index finger of your left hand into the omental foramen (Figure 4.21). Anterior to your finger is the hepatoduodenal ligament and its contents: bile ducts, hepatic artery proper, hepatic portal vein, autonomic nerves, and lymphatics.
3. To aid dissection, place a strip of white paper into the omental foramen (Figure 4.24).
4. Use blunt dissection to remove the peritoneum from the anterior surface of the hepatoduodenal ligament (anterior to the vessels and ducts).
5. Identify the three large structures that are contained within the hepatoduodenal ligament: common bile duct, hepatic artery proper, and hepatic portal vein (Figure 4.24). The bile duct is the most lateral of the three.
6. Use a probe to trace the bile duct superiorly. Identify the cystic duct and the common hepatic duct (Figure 4.25).
7. Follow the common hepatic duct superiorly until it receives its tributaries, the right hepatic duct and the left hepatic duct. The right and left hepatic ducts exit the porta hepatis.
8. NOTE: Before beginning a dissection of arteries supplying the GI tract, be aware that there can be a considerable amount of variation. Use caution. As a general rule of thumb, you name the artery based on what structure it is supplying, even if the origin varies from what is considered “normal”.
9. Clean the hepatic artery proper. The tough “connective tissue” around these vessels contains an autonomic nerve plexus. To clear the dissection field, remove the autonomic nerves.
10. Follow the hepatic artery proper toward the liver through the hepatoduodenal ligament. At the porta hepatis the hepatic artery proper branches into the left hepatic artery and the right hepatic artery (Figure 4.25).
11. Two other arteries arise in the hepatoduodenal ligament (Figure 4.25):
o Cystic artery arises from the right hepatic artery. Follow it to the gallbladder.
o Right gastric artery arises from the hepatic artery proper. Follow it to the lesser curvature of the stomach.
12. Lymphatics are also contained within the hepatoduodenal ligament. The lymphatic vessels are too small to dissect but hepatic lymph nodes can be seen. The lymph nodes may be removed to clear the dissection field.
13. Follow the hepatic artery proper inferiorly and confirm that it is a branch of the common hepatic artery (Figure 4.25).
14. Observe that the common hepatic artery gives rise to the gastroduodenal artery. The gastroduodenal artery passes posterior to the first part of the duodenum (Figure 4.26). Follow the gastroduodenal artery until it divides to give rise to the right gastro-omental (gastroepiploic) artery and the anterior superior pancreaticoduodenal artery.
15. Follow the common hepatic artery to the left toward the celiac trunk (Figure 4.26). Note that the celiac trunk arises from the anterior surface of the abdominal aorta at the level of the 12th thoracic vertebra. The celiac trunk is very short (less than 2 cm in most cases) and divides into three branches:
o Common hepatic artery (already dissected)
o Left gastric artery
o Splenic artery
16. Use blunt dissection to follow the left gastric artery toward the esophagus and stomach (Figure 4.26). The left gastric artery reaches the stomach near the esophagus and then follows the lesser curvature of the stomach within the lesser omentum. The left gastric artery forms an anastomosis with the right gastric artery along the lesser curvature of the stomach. Branches of the gastric arteries distribute to the anterior and posterior surfaces of the stomach.
17. Follow the splenic artery to the left for about 5 cm and verify that it lies against the posterior abdominal wall. The splenic artery courses along the superior border of the pancreas and may be partially imbedded in it. Do not dissect the splenic artery from the pancreas at this time. Note that short gastric arteries arise from the splenic artery to supply the fundus of the stomach (Figure 4.26).
18. Find the left gastro-omental (gastroepiploic) artery in the greater omentum about 2 cm from the greater curvature of the stomach (Figure 4.26). The left gastro-omental artery is a branch of the splenic artery.
19. Find the right gastro-omental artery in the greater omentum near the right end of the greater curvature of the stomach. The right gastro-omental artery anastomoses with the left gastro-omental artery. Follow the right gastro-omental artery to the right to find its origin from the gastroduodenal branch of the common hepatic artery.
20. Return to the hepatoduodenal ligament and identify the hepatic portal vein. The hepatic portal vein lies posterior to both the hepatic artery proper and the bile duct (Figure 4.24). Follow the hepatic portal vein superiorly and observe that it passes into the porta hepatis, where it divides into right and left portal veins. The hepatic portal vein usually receives the left and right gastric veins as tributaries. Inferiorly, the hepatic portal vein passes posterior to the first part of the duodenum.
IN THE CLINIC: Anatomical Variation in Arteries
In about 12% of cases the right hepatic artery arises from the superior mesenteric artery. An aberrant left hepatic artery may arise from the left gastric artery. During surgical removal of the stomach (gastrectomy), blood flow to an aberrant left hepatic artery could be interrupted, endangering the left lobe of the liver.
The cystic artery usually arises from the right hepatic artery, but other origins are possible. The cystic artery may pass posterior (75%) or anterior (24%) to the common hepatic duct (Figure 4.27).
Spleen
The spleen is the largest hematopoietic organ in the body. Its size and weight may vary considerably depending upon the blood volume that it contains. The spleen is covered by visceral peritoneum except at the hilum where the splenic vessels enter and leave.
1. Use your left hand to retract the fundus of the stomach to the right. Use your right hand to gently pull the spleen anteriorly.
2. Observe that the spleen has a smooth diaphragmatic surface. The spleen has sharp anterior, inferior, and superior borders. The superior border of the spleen is often notched.
3. The visceral surface of the spleen is related to four organs:
o Stomach
o Left kidney
o Transverse colon (left colic flexure)
o Pancreas
4. The diaphragmatic surface of the spleen is related (through the diaphragm) to ribs 9, 10, and 11 (Figure 4.28).
IN THE CLINIC: Spleen
The relationship of the spleen to ribs 9, 10, and 11 is of clinical importance in evaluating rib fractures and penetrating wounds. A lacerated spleen bleeds profusely into the abdominal cavity and may have to be removed surgically (splenectomy). It must be emphasized that there is a risk of puncturing the spleen during pleural tap (thoracocentesis).
An enlarged spleen (splenomegaly) may be encountered during physical examination. The spleen is considered enlarged when it can be palpated inferior to the costal margin.
Liver
The liver is the largest gland in the body, comprising about 2.5% of the body weight of an adult. To study the surface features of the liver, it must be detached from the diaphragm.
1. Review the falciform ligament and the coronary ligament of the liver.
2. Use scissors to cut the falciform ligament along its attachment to the anterior abdominal wall. Extend the cut superiorly and cut the right and left triangular ligaments along the inferior surface of the diaphragm.
3. Insert your fingers between the liver and the diaphragm and tear the connective tissue that attaches the liver to the diaphragm. Cut the posterior layer of the coronary ligament.
4. Extend the cut previously made in the diaphragm toward the inferior vena cava. Use scissors to cut the inferior vena cava between the liver and the diaphragm. Elevate the inferior border of the liver and cut the inferior vena cava again, as close to the inferior surface of the liver as possible. These two cuts will leave a short segment of the inferior vena cava within the liver (Figure 4.29B).
5. The liver should now be freely mobile but attached to the other abdominal viscera by the bile duct, hepatic artery proper, and hepatic portal vein. Move the liver carefully to avoid tearing these structures.
6. Examine the liver and note that the right lobe is six times larger than the left lobe. The sharp inferior border of the liver separates the visceral surface from the diaphragmatic surface.
7. Identify the bare area on the posterior aspect of the diaphragmatic surface. Here, the liver was adjacent to the diaphragm and not covered by peritoneum. Around the bare area, note the cut edges of the coronary ligament.
8. Examine the visceral surface of the liver (Figure 4.29A). An H-shaped set of fissures and fossae defines four lobes. Identify the right lobe, left lobe, caudate lobe, and quadrate lobe.
9. Observe that the ligamentum venosum and falciform ligament occupy the left fissure of the “H” (Figure 4.29B). The gallbladder and inferior vena cava occupy the fossae that form the right side of the “H.”
10. Identify the porta hepatis. It forms the horizontal bar of the “H.” The structures passing through the hepatoduodenal ligament (bile ducts, hepatic arteries, hepatic portal vein, lymphatics, and autonomic nerves) enter or leave the liver at the porta hepatis.
11. Examine the small segment of the inferior vena cava that is attached to the liver. Note that several hepatic veins drain directly into the inferior vena cava (Figure 4.29B).
12. Use a textbook to study the two conventions by which the liver may be divided into lobes. The falciform ligament divides the liver into right and left anatomical lobes. The pattern of its bile drainage and vascular supply are used to divide the liver into right and left functional lobes.
13. The liver has a substantial lymphatic drainage. At the porta hepatis, small lymph vessels drain into hepatic lymph nodes. From the hepatic lymph nodes, lymphatic vessels follow the hepatic arteries to celiac lymph nodes located around the celiac trunk.
IN THE CLINIC: Liver
The liver may undergo pathologic changes that could be encountered during dissection. The liver may be enlarged. This happens in liver congestion due to cardiac insufficiency (cardiac liver). In contrast, the liver may be small and have fibrous nodules. Such a finding may indicate cirrhosis of the liver. Because the liver is essentially a capillary bed downstream from the gastrointestinal tract, metastatic tumor cells are often trapped within it, resulting in secondary tumors.
Gallbladder
The gallbladder is a reservoir for the storage and concentration of bile. The gallbladder occupies a shallow fossa on the visceral surface of the liver (Figure 4.29B). The gallbladder is usually stained dark green by bile, which leaks through the wall of the gallbladder after death.
1. Replace the liver into its correct anatomical position.
2. Confirm that the gallbladder is located near the tip of the ninth costal cartilage in the midclavicular line (Figure 4.17).
3. Reposition the liver to expose the visceral surface. Use blunt dissection to remove the gallbladder from its fossa.
4. Identify the parts of the gallbladder (Figure 4.30):
o Neck
o Body
o Fundus
5. Review the course of the cystic artery. The cystic artery may be stained green by bile and is often fragile and difficult to dissect.
6. Use scissors to make a longitudinal incision through the wall of the gallbladder, beginning at the fundus and continuing through the neck. If gallstones are present, remove them. Look for the spiral fold, which is a fold in the mucosal lining of the neck that continues into the cystic duct.
Dissection Review
1. Replace the organs in their correct anatomical positions.
2. Close and open the flaps of the abdominal wall and review the location of each organ relative to the abdominal quadrant system.
3. Use an illustration and the dissected specimen to trace the branches of the celiac trunk.
4. Review the relationships of the structures in the hepatoduodenal ligament.
5. Review the boundaries of the omental foramen.
6. Review the parts of the organs dissected and their relationships to surrounding structures.
7. Use an embryology textbook to review the development of the liver and the ventral mesogastrium.
8. Review the derivatives of the embryonic foregut.
MONDAY, JANUARY 11 -Superior Mesenteric Artery and Small Intestine / INFERIOR MESENTERIC ARTERY AND LARGE INTESTINE
Dissection Overview
The order of dissection will be as follows: The mesentery will be examined. The branches of the superior mesenteric artery that supply the jejunum, ileum, cecum, ascending colon, and transverse colon will be dissected. The remainder of the field of supply of the superior mesenteric artery (to the duodenum and pancreas) will be dissected later, because these structures lie behind the attachment of the transverse mesocolon. The external features of the jejunum and ileum will be studied.
Dissection Instructions
Small Intestine
The small intestine consists of the duodenum, jejunum, and ileum. The function of the small intestine is to absorb nutrients from food. It has elaborate folds of mucosa that increase surface area and a rich blood supply to transport the absorbed nutrients. The jejunum (proximal two-fifths) and ileum (distal three-fifths) will be studied together since their transition is not obvious.
1. Move the small intestine to the left side of the abdominal cavity and follow the jejunum proximally (Figure 4.34). Find the duodenojejunal junction.
2. Find the suspensory ligament of the duodenum, which is a fibromuscular ligament that arises from the right crus of the diaphragm and anchors the intestine at the duodenojejunal junction (Figure 4.34, inset).
3. Palpate the small intestine and note that the wall of the jejunum is thicker than the wall of the ileum.
4. Identify the termination of the ileum where it empties into the cecum at the ileocecal junction (Figure 4.34).
5. Verify that the root of the mesentery crosses the posterior abdominal wall from the duodenojejunal junction in the left upper quadrant to the ileocecal junction in the right lower quadrant (Figure 4.34). The root of the mesentery is about 15 cm long. The intestinal attachment of the mesentery is nearly 6 m long.
Superior Mesenteric Artery
The superior mesenteric artery arises from the anterior surface of the abdominal aorta about 1 cm inferior to the celiac trunk (L1 vertebral level). At its origin, the superior mesenteric artery lies posterior to the neck of the pancreas. As the superior mesenteric artery emerges from posterior to the neck of the pancreas, it passes anterior to the uncinate process of the pancreas, the third part of the duodenum, and the left renal vein. The superior mesenteric artery then enters the mesentery. Within the mesentery the superior mesenteric artery courses toward the terminal end of the ileum.
1. Return the liver to its correct anatomical position.
2. Turn the transverse colon and greater omentum superiorly over the costal margin. The posterior surface of the transverse mesocolon should face anteriorly (Figure 4.31).
3. Move the coils of the jejunum and ileum to the left side of the abdomen so that the right side of the mesentery faces anteriorly (Figure 4.31). Observe that the root of the mesentery is attached to the posterior abdominal wall along a line from the left upper quadrant to the right lower quadrant.
4. Note that the mesentery contains branches of the superior mesenteric artery and vein, autonomic nerves, lymphatics, and adipose tissue, sandwiched between two layers of peritoneum. Remove the peritoneum on the right side of the mesentery to expose the branches of the superior mesenteric artery. To do this, use a probe to gently scrape the peritoneum so that only the right layer is torn (the left layer of peritoneum should be left intact). Then grasp the torn peritoneum between your thumb and index finger. Peel it slowly, using the handle of a forceps to scrape the peritoneum free from deeper structures.
5. Remove the parietal peritoneum from the posterior abdominal wall to the right of the mesentery. Remove the peritoneum as far laterally as the ascending colon.
6. Identify the superior mesenteric artery. Use blunt dissection to trace the superior mesenteric artery proximally and observe that it crosses anterior to the third part of the duodenum. Note that the third part of the duodenum and the left renal vein can become compressed between the superior mesenteric vessels and the abdominal aorta.
7. Use blunt dissection to clean the branches of the superior mesenteric artery. As you dissect, note the dense autonomic nerve network surrounding the vessels. This is the superior mesenteric plexus of nerves. Remove the nerves as necessary to clear the dissection field.
8. Identify the branches of the superior mesenteric artery (Figure 4.31):
o Inferior pancreaticoduodenal artery is the first branch of the superior mesenteric artery. The inferior pancreaticoduodenal artery will be dissected later.
o Intestinal arteries – 15 to 18 arteries to the jejunum and the ileum. Intestinal arteries end in straight terminal branches called vasa rectae (Figure 4.32). Arcades connect the intestinal arteries. Observe the blood supply to the proximal jejunum and note that only one or two arcades are found between adjacent intestinal arteries, resulting in relatively long vasa recta (Figure 4.32A). Examine the distal ileum and note that four or five arcades occur between adjacent intestinal arteries, resulting in relatively short vasa rectae (Figure 4.32B).
o Ileocolic artery supplies the cecum. The ileocolic artery gives rise to the appendicular artery (Figure 4.33). The ileocolic artery anastomoses with intestinal branches and with the right colic artery.
o Right colic artery supplies the ascending colon (Figure 4.31). The right colic artery arises from the right side of the superior mesenteric artery and passes to the right in a retroperitoneal position. It divides into a superior branch and an inferior branch.
o Middle colic artery supplies the transverse colon (Figure 4.31). The middle colic artery arises from the anterior surface of the superior mesenteric artery and courses through the transverse mesocolon. It divides into a right branch and a left branch.
9. Identify the superior mesenteric vein. The superior mesenteric vein courses along the right side of the superior mesenteric artery. The superior mesenteric vein is formed by branches that correspond in name and position to the branches of the superior mesenteric artery. Posterior to the pancreas, the superior mesenteric vein joins the splenic vein to form the hepatic portal vein.
10. The mesentery may contain up to 200 mesenteric lymph nodes. Identify one or two of these lymph nodes along the branches of the superior mesenteric vessels. The superior mesenteric lymph nodes are located near the origin of the superior mesenteric artery from the abdominal aorta. Lymph nodes may be removed to clear the dissection field.
Dissection Review
1. Replace the small intestine in its correct anatomical position.
2. Close and open the flaps of the abdominal wall and review the location of the jejunum and ileum relative to the abdominal quadrant system.
3. Review the relationships of the jejunum and ileum to surrounding structures.
4. Use an illustration and the dissected specimen to review the branches of the superior mesenteric artery.
5. Use an embryology textbook to review the derivatives of the embryonic midgut.
Inferior Mesenteric Artery and Large Intestine
Dissection Overview
The inferior mesenteric artery arises from the anterior surface of the abdominal aorta at the level of the intervertebral disc between vertebrae L2 and L3. The objective is to demonstrate the field of supply of the inferior mesenteric artery (left third of the transverse colon, descending colon, sigmoid colon, and most of the rectum). Except for the branches that pass through the transverse mesocolon to anastomose with the middle colic artery, and those that pass through the sigmoid mesocolon to supply the sigmoid colon, the inferior mesenteric artery and its branches lie retroperitoneally.
The order of dissection will be as follows: The external features of the large intestine will be studied. The inferior mesenteric artery and its branches will be dissected.
Dissection Instructions
Large Intestine
The large intestine consists of the cecum (with attached appendix), colon (ascending, transverse, descending, and sigmoid), rectum, and anal canal. Absorption of water from fecal material is a major function of the large intestine. The relatively smooth mucosal surface of the large intestine is well suited for this function, as a smooth surface is less likely to impede the movement of progressively more solid fecal matter.
1. Return the small intestine and transverse colon to their correct anatomical positions.
2. In the right lower quadrant, identify the cecum (L. caecus, blind) (Figure 4.33). The length of its mesentery and the degree of its mobility vary considerably from individual to individual.
3. The appendix (vermiform appendix) (L. appendere, to hang on) is attached to the end of the cecum. The appendix may be found in one of several positions (Figure 4.36). Recall that the appendix is suspended on a mesentery called the mesoappendix. The appendicular artery is found within the mesoappendix (Figure 4.33).
4. Identify the ascending colon. The ascending colon extends from the cecum to the right colic flexure (Figure 4.19).
5. Identify the transverse colon. The transverse colon extends from the right colic flexure to the left colic flexure. Observe that the left colic flexure is at a more superior level than the right colic flexure. Between the two flexures, the transverse colon is freely movable.
6. Observe the descending colon. It is a secondarily retroperitoneal organ. The descending colon descends from the left colic flexure to the left lower quadrant (Figure 4.19).
7. In the left lower quadrant, find the sigmoid colon. Observe that the sigmoid colon has a mesentery (sigmoid mesocolon) and is mobile. The sigmoid colon ends in the pelvic cavity at the level of the third sacral segment, where it becomes continuous with the rectum.
8. The rectum is contained entirely within the pelvic cavity and will be dissected with the pelvic viscera.
9. Observe the external surface of the large intestine and note three features that distinguish it from the small intestine (Figure 4.35):
o Teniae coli – three narrow bands of longitudinal muscle –only one band is visible anteriorly
o Haustra – outpouchings of the wall of the colon
o Omental appendices (epiploic appendages) – small accumulations of fat covered by visceral peritoneum
Inferior Mesenteric Artery
1. Turn the transverse colon and greater omentum superiorly over the costal margin to expose the posterior surface of the transverse mesocolon.
2. Move the small intestine to the right so that the descending colon is visible from the left colic flexure to the sigmoid colon (Figure 4.35).
3. The origin of the inferior mesenteric artery lies posterior to the third part of the duodenum. If you have trouble finding it, find one of its branches in the sigmoid mesocolon and trace the branch back to the main vessel. Then proceed with the dissection of the peripheral branches.
o Dissection note: The left ureter could be mistaken for the inferior mesenteric artery or one of its branches. The inferior mesenteric artery and vein and the ureter all lie in the retroperitoneal space, but the vessels pass anterior to the ureter.
4. Use a probe to clean the branches of the inferior mesenteric artery (Figure 4.35):
o Left colic artery supplies the descending colon and the left third of the transverse colon. The left colic artery anastomoses with the middle colic branch of the superior mesenteric artery.
o Sigmoid arteries – three or four arteries that supply the sigmoid colon. Sigmoid arteries pass through the sigmoid mesocolon. Note that they form arcades similar to those of the intestinal arteries.
o Superior rectal artery supplies the proximal part of the rectum. The superior rectal artery divides into a right branch and a left branch. The right and left branches of the superior rectal artery descend into the pelvis on either side of the rectum. Do not follow them into the pelvis.
5. Observe the tributaries of the inferior mesenteric vein. The tributaries of the inferior mesenteric vein correspond to the branches of the inferior mesenteric artery. The inferior mesenteric vein ascends on the left side of the inferior mesenteric artery, passes posterior to the pancreas, and joins either the splenic vein or (less frequently) the superior mesenteric vein.
6. The inferior mesenteric artery and vein are accompanied by lymph vessels that drain into the inferior mesenteric nodes around the origin of the inferior mesenteric artery.
7. Review the branches of the superior mesenteric artery and inferior mesenteric artery that supply the large intestine.
Dissection Review
1. Close and open the flaps of the abdominal wall to review the location of each part of the large intestine relative to the abdominal quadrant system.
2. Review the relationship of each part of the large intestine to surrounding structures.
3. Use an illustration and the dissected specimen to trace the branches of the inferior mesenteric artery.
4. Use an embryology textbook to review the derivatives of the embryonic hindgut.
TUESDAY, JANUARY 12 and Wednesday, January 13 – duodenum and Pancreas / Removal of the Gastrointestinal Tract
Dissection Overview
The duodenum is the part of the small intestine between the stomach and the jejunum. The duodenum is the drainage point for the ducts of the liver and pancreas. The pancreas lies within the bend of the duodenum. The pancreas is both an endocrine and an exocrine organ and has a rich blood supply arising from the celiac trunk and the superior mesenteric artery.
The order of dissection will be as follows: The duodenum and pancreas will be studied in situ. The formation of the hepatic portal vein will be demonstrated. The gastrointestinal tract will be removed and studied ex vivo. The main pancreatic duct will be dissected.
Dissection Instructions
Duodenum
1. Turn the transverse colon and greater omentum superiorly over the costal margin (Figure 4.35).
2. Use blunt dissection to remove the remaining connective tissue and peritoneum from the anterior surface of the duodenum and pancreas.
3. Observe the four parts of the duodenum (Figure 4.37):
o Superior (first) part – at the level of vertebra L1. The superior part of the duodenum lies in the transverse plane and the hepatoduodenal ligament is attached to it. It is mostly intraperitoneal.
o Descending (second) part – at the level of vertebra L2. The descending part of the duodenum is positioned to the right of the midline and anterior to the right kidney, right renal vessels, and inferior vena cava. It is retroperitoneal. The bile duct and the pancreatic duct drain into the descending part of the duodenum.
o Horizontal (third) part – at the level of vertebra L3. The horizontal part of the duodenum lies anterior to the inferior vena cava and the abdominal aorta. It is retroperitoneal. The horizontal part of the duodenum is crossed anteriorly by the superior mesenteric vessels and posteriorly by the inferior mesenteric vessels.
o Ascending (fourth) part – ascends to the level of vertebra L2. The ascending part of the duodenum is retroperitoneal throughout most of its length. The ascending part of the duodenum turns anteriorly to join the jejunum at the duodenojejunal junction.
Pancreas
Identify the pancreas within the bend of the duodenum. Note that it is a secondarily retroperitoneal organ that lies across the midline and that it is positioned against vertebral bodies L1 to L3. Identify the parts of the pancreas (Figure 4.37):
o Head – lies within the curve of the duodenum. The uncinate process is a small projection (to be identifed later) from the inferior margin of the head that passes posterior to the superior mesenteric vessels. The inferior vena cava lies posterior to the head of the pancreas.
o Neck – a short portion that lies anterior to the superior mesenteric vessels and connects the head of the pancreas to the body.
o Body – extends from right to left and slightly superiorly as it crosses the posterior abdominal wall. The abdominal aorta lies posterior to the body of the pancreas.
o Tail – the narrow left
end of the gland. The tip of the tail lies in the splenorenal ligament and
contacts the hilum of the spleen.
Hepatic Portal Vein
Use an illustration to review the hepatic portal venous system. The superior mesenteric vein and the splenic vein join to form the hepatic portal vein posterior to the neck of the pancreas. The hepatic portal vein carries venous blood to the liver from the abdominal portion of the gastrointestinal tract, the spleen, and the pancreas.
1. The splenic vein courses posterior to the pancreas, inferior to the splenic artery. Use a probe to dissect posterior to the body of the pancreas and find the splenic vein.
2. Follow the splenic vein to the right, where it is joined by the superior mesenteric vein. This is the origin of the hepatic portal vein. Recall that the hepatic portal vein ascends in the hepatoduodenal ligament to the porta hepatis.
3. Return to the field of distribution of the inferior mesenteric vein. Find it and follow it superiorly. The inferior mesenteric vein usually joins the splenic vein, but it may join the superior mesenteric vein or the junction of the superior mesenteric and splenic veins.
4. Use a textbook or atlas to review the portal-systemic (portal-caval) anastomoses:
o Gastroesophageal – left gastric vein/esophageal veins/azygos vein
o Anorectal – superior rectal vein/middle and inferior rectal veins
o Paraumbilical – paraumbilical veins/superficial epigastric veins
o Retroperitoneal – colic veins/retroperitoneal veins
IN THE CLINIC: Portal Hypertension
The hepatic portal system of veins has no valves. When the hepatic portal vein becomes blocked, blood pressure increases in the hepatic portal system (portal hypertension) and its tributaries become engorged. Portal hypertension causes hemorrhoids and varicose gastric and esophageal veins. Bleeding from ruptured gastroesophageal varices is a dangerous complication of portal hypertension.
Removal of the Gastrointestinal Tract
Dissection Overview
The order of dissection will be as follows: The rectum will be cut, using ligatures to prevent spilling its contents. The arteries to the gastrointestinal tract (celiac trunk, superior mesenteric artery, and inferior mesenteric artery) will be cut. The esophagus will be cut. The gastrointestinal tract will then be removed and reviewed outside of the body. The gastrointestinal tract will be taken to a sink and selected areas will be opened and rinsed in order to study their internal features.
Dissection Instructions
1. Tie two strings 4 cm apart at the junction between the sigmoid colon and the rectum. Use scissors to cut the large intestine between the strings.
2. Cut the sigmoid arteries and left colic artery 1 cm distal to where they arise from the inferior mesenteric artery. Cut the superior rectal vein where it arises from the inferior mesenteric vein. Do not cut the superior rectal artery.
3. Cut the parietal peritoneum lateral to the descending colon and use your fingers to free the descending colon from the posterior abdominal wall. Roll the sigmoid and descending colons toward the midline and use your fingers to loosen its blood vessels from the posterior abdominal wall.
4. Use scissors to cut the parietal peritoneum lateral to the ascending colon and use your fingers to free the ascending colon from the posterior abdominal wall. Roll the ascending colon toward the midline and use your fingers to loosen its blood vessels from the posterior abdominal wall.
5. Reflect the ileum, jejunum, and mesentery superiorly to expose the superior mesenteric artery where it arises from the abdominal aorta.
6. The inferior pancreaticoduodenal artery is usually the most proximal branch of the superior mesenteric artery, although its origin is variable (Figure 4.38). The inferior pancreaticoduodenal artery enters the inferior portion of the head of the pancreas.
7. Reflect the superior mesenteric artery superiorly at its origin from the abdominal aorta. The uncinate process of the pancreas is located posterior the superior mesenteric artery, superior to the left renal vein, and to the left of the inferior vena cava.
8. Use scissors to cut the superior mesenteric artery near the aorta, leaving a 1-cm stump.
9. Gently detach the uncinate process from the posterior abdominal wall.
10. Inferior to the diaphragm, cut the esophagus. Cut the vagal nerve trunks at the same level.
11. Use scissors to cut the suspensory ligament of the duodenum close to the duodenojejunal junction.
12. Grasp the spleen and gently pull it medially. Insert your fingers posterior to the spleen and carefully free the splenic vessels, tail of the pancreas, and body of the pancreas from the posterior abdominal wall. Carefully reflect the spleen, stomach, and intestines from left to right to expose the celiac trunk and ganglion.
13. Identify the greater splanchnic nerve where it passes into the celiac gangion. Spare the greater splanchnic nerve.
14. Cut any autonomic nerve fibers emerging from the celiac ganglion as they jump onto the celiac artery and its branches.
15. Use scissors to cut the celiac trunk distal to the celiac ganglion, but proximal to the common hepatic, left gastric, and splenic arteries.
16. Free the stomach from any peritoneal attachments it may still have to the posterior abdominal wall.
17. Insert your fingers posterior to the duodenum and free it from the posterior abdominal wall.
18. The gastrointestinal tract, liver, gallbladder, pancreas, and spleen should now be free of attachments. Remove them from the abdominal cavity. Be careful not to twist or tear the structures in the hepatoduodenal ligament.
19. Arrange the abdominal viscera on the dissecting table in their anatomical positions and study the parts from the anterior view:
o Trace the branches of the celiac trunk, superior mesenteric artery, and inferior mesenteric artery to their areas of distribution.
o Observe the formation and termination of the hepatic portal vein.
o Note the differences between the branching pattern of the arteries and the veins.
o Turn the viscera and repeat the exercise from the posterior view.
20. Carry the viscera to a sink to examine their internal features.
21. Use scissors to open the stomach along its anterior surface. Extend the cut into the first part of the duodenum. Rinse the mucosa and observe the following features (Figure 4.39):
o Gastric folds (rugae)
o Pyloric antrum
o Pyloric canal
o Pyloric sphincter
o Pyloric orifice
Palpate the differences in the thicknesses of the walls of the stomach, first part of the duodenum, and the pyloric sphincter.
22. Use scissors to make a longitudinal incision in the anterior wall of the duodenum. In the second part of the duodenum identify the following (Figure 4.40):
o Circular folds (plicae circulares)
o Major (greater) duodenal papilla – an elevation of mucosa on the medial wall of the second part of the duodenum. The major duodenal papilla is the shared opening of the main pancreatic duct and bile duct.
o Minor (lesser) duodenal papilla – the site of drainage of the accessory pancreatic duct. If present, it will be approximately 2 cm superior to the major duodenal papilla.
23. Use scissors to make a 5-cm longitudinal incision in the proximal jejunum and another in the distal ileum. Rinse the mucosa and compare features. Note that the circular folds are larger and closer together in the jejunum (Figure 4.41).
24. Use scissors to make an incision approximately 7.5 cm long in the anterior wall of the cecum. Rinse the mucosa and identify the following (Figure 4.42):
o Ileocecal orifice
o Superior and inferior lips of the ileocecal valve
o Opening of the appendix
25. Make an incision approximately 5 cm long in the anterior surface of the transverse colon. Note the semilunar folds (plicae semilunares) between adjacent haustra. Observe the relative smoothness of the mucosa.
26. Turn the viscera so that the posterior side is facing up.
27. Use a probe to gently dissect into the posterior surface of the head of the pancreas and find the main pancreatic duct. Trace the main pancreatic duct through the neck and into the body. The accessory pancreatic duct joins the superior side of the main pancreatic duct.
28. Follow the main pancreatic duct toward the descending part of the duodenum. Observe that the main pancreatic duct is joined by the bile duct.
29. Identify the posterior superior and anterior superior pancreaticoduodenal arteries (Figure 4.38). Both are branches of the gastroduodenal artery.
30. Return to the celiac trunk and follow the splenic artery as it passes to the left along the superior margin of the pancreas (Figure 4.38). Up to 10 small branches of the splenic artery supply the body and tail of the pancreas. Identify only two:
o Dorsal pancreatic artery – enters the neck of the pancreas
o Greater pancreatic (pancreatica magna) artery – enters the pancreas at the junction of the medial two-thirds and lateral one-third of the gland
31. Follow the splenic artery to the hilum of the spleen and identify the left gastro-omental artery. Complete the dissection of the left gastro-omental artery by following it through the greater omentum to its anastomosis with the right gastro-omental artery.
32. The veins of the pancreas correspond to the arteries. They drain into the superior mesenteric and splenic veins and ultimately are tributaries to the hepatic portal vein.
33. The viscera may be stored in a large plastic bag or in the abdominal cavity. Wet these specimens frequently with mold-inhibiting solution.
Dissection Review
1. Review the features of the gastrointestinal mucosa. Compare the quantity and complexity of circular folds in the proximal and distal parts of the small intestine. Compare this arrangement to the mucosal features seen in the stomach and large intestine. Correlate your findings to the function of the organs dissected.
2. Recall the locations of valves in the gastrointestinal tract.
3. Review the relationship of each part of the duodenum to surrounding structures.
4. Review the branches of the celiac trunk and superior mesenteric artery.
5. Use an illustration and the dissected specimen to reconstruct the blood supply to the pancreas and duodenum.
6. Review the formation and field of drainage of the hepatic portal vein.
7. Trace a drop of blood from the small intestine to the inferior vena cava, naming all veins that are encountered along the way.
8. Use an embryology textbook to review the development of the liver, pancreas, and duodenum.
1. Differentiate between the abdominal cavity and the peritoneal cavity.
2. What is the suspensory ligament of the duodenum?
3. Locate the ileocecal junction. At what level is it found?
4. Examine "the mesentery" (of the jejunum and ileum), noting its body wall attachment. How long is this attachment? What structures does it cross?
5. What is the location of the small intestine within the peritoneal cavity?
6. What parts of the large intestine are peritoneal. What parts are retroperitoneal?
7. Consider the derivation of the anterior cecal fold (vascular), the ileocecal fold, the mesoappendix, the transverse mesocolon, and the sigmoid mesocolon with regard to gut development.
8. Why are some parts peritoneal or retroperitoneal?
As gut development proceeds some parts get squished against the posterior body wall and stick there.
9. What happens to the primitive mesentery of the retroperitoneal part of the large intestine?
10. What is the significance of fusion fascia?
11. Where does the superior mesenteric artery terminate?
12. Describe the superior mesenteric vein and its branches.
13. Is there a separate ascending branch of the left colic artery accompanying the inferior mesenteric vein?
18. Examine the arteriae rectae of the large intestine. How do they differ from those of the small intestine?
19. What constitutes the marginal artery?
21. Define the omental bursa (lesser sac). How does it develop? What is its entrance? What are its boundaries?
22. Follow along the proper hepatic artery into the hepatoduodenal ligament until you locate the right gastric artery. Trace it to the lesser curvature of the stomach. Does it anastomose with the left gastric artery?
23. Does the left gastro-omental artery anastomose with the right?
24. How does the splenic artery reach the spleen? How do its branches reach the stomach? (Note relations to stomach, kidney and left colic (splenic) flexure.)
25. Look for a hepatic branch of the anterior vagal trunk passing within the lesser omentum to the liver and then to the duodenum. Do you have an accompanying hepatic branch of the left gastric artery?
26. How do sympathetic branches distribute to the stomach?
27. Is the superior (1st) part of the duodenum peritoneal or retroperitoneal?
28. What is the suspensory muscle of the duodenum?
29. What is the relation of the horizontal (3rd) part of the duodenum to the superior and inferior mesenteric arteries?
30. Carefully trace the common bile duct as it courses behind the first part of the duodenum and the head of the pancreas to the medial wall of the second part of the duodenum. Does an artery cross it?
31. How does the posterior arcade differ from the anterior arcade?
32. Do you find veins with the arterial arcades of the pancreas and duodenum?
33. Does the splenic vein receive the inferior mesenteric vein?
34. Into which part of the duodenum do the common bile and pancreatic ducts open?
35. Where are the cystic veins?
36. What are the fetal functions of the round ligament of the liver (ligamentum teres hepatis, a remnant of the obliterated umbilical vein), and the ligamentum venosum?
37. Identify the hepatic veins. How many are there?
38. Did you find any hepatic lymph nodes?
39. Review all of the tributaries of the portal vein and completely organize its drainage pattern. What organs does it drain?
Posterior Abdominal Viscera
LEARNING OBJECTIVES: Upon completion of this session, the student will be able to:
2. Describe the basic internal gross anatomy of the kidney.
3. Define the blood supply and drainage of the kidneys and suprarenal glands.
4. Describe the general organization of the urinary and endocrine systems.
6. Know the three major passageways through the diaphragm and the structures traversing them.
10. Describe the parasympathetic innervation of the GI tract.
FRIDAY, JANUARY 15 – POSTERIOR ABDOMINAL REGION / DIAPHRAGM
Dissection Overview
The posterior abdominal viscera are located in an area that is referred to as the retroperitoneal space. The retroperitoneal space is not a real space. It is that part of the body between the parietal peritoneum and the muscles and bones of the posterior abdominal wall (Figure 4.43). The retroperitoneal space contains the kidneys, ureters, suprarenal glands, aorta, inferior vena cava, and abdominal portions of the sympathetic trunks.
The order of dissection will be as follows: The posterior abdominal viscera will be palpated. The kidneys and suprarenal glands will be removed from the renal fascia and studied. The abdominal aorta and the inferior vena cava will be dissected. The muscles of the posterior abdominal wall will be studied. The lumbar plexus of nerves will be examined. Finally, the diaphragm will be studied.
Dissection Instructions
1. Use a sponge or white linen towels to clean the posterior abdominal wall.
2. Palpate the kidneys and the suprarenal (adrenal) glands. They lie lateral to the vertebral column at vertebral levels T12 to L3.
3. Palpate the abdominal aorta.
4. To the right of the abdominal aorta, palpate the inferior vena cava.
5. Remove any remaining parietal peritoneum from the posterior abdominal wall.
6. If you are dissecting a female cadaver, go to step 10. Partner with a dissection team that has a male cadaver to review the testicular vessels. You are expected to know the anatomical details for both sexes.
7. Identify the testicular artery and vein at the deep inguinal ring. The testicular artery is quite small and delicate. Follow the testicular vessels superiorly and note that they cross anterior to the ureter. Do not damage the ureter.
8. The right and left testicular arteries branch directly from the aorta at about vertebral level L2 (Figure 4.45). This origin is inferior to the origin of the renal arteries.
9. Observe that the left testicular vein drains into the left renal vein. The right testicular vein drains directly into the inferior vena cava.
10. If you are dissecting a male cadaver, go to the next section. Partner with a dissection team that has a female cadaver to review the ovarian vessels. You are expected to know the anatomical details for both sexes.
11. In the female cadaver, identify the ovarian vessels. Their origin is comparable to that of the testicular vessels in the male. Note that the ovarian vessels cross anterior to the ureter.
12. Inferiorly, the ovarian vessels end in the pelvic cavity. Follow the ovarian vessels inferiorly until they cross the external iliac vessels. Do not follow them into the pelvis at this time.
IN THE CLINIC: Testicular Varicocele
Varicocele is a varicose condition of the pampiniform plexus of veins. Varicocele is more common on the left side because the left testicular vein drains into the left renal vein, and the left renal vein is subject to compression where it passes between the superior mesenteric artery and abdominal aorta.
Kidneys
The retroperitoneal position of the kidneys is well illustrated on transverse section (Figure 4.43). The kidneys are well protected by their position within the body as well as by a cushioning layer of fat.
1. Note that the kidney lies against the posterior abdominal wall. The anterior surface of the kidney faces anterolaterally (Figure 4.43).
2. Use your fingers to separate the kidney from the perirenal fat and renal fascia (Figure 4.43).
3. Note the size and shape of the kidney.
4. Identify the left renal vein (Figure 4.46). Use a probe to trace the left renal vein from the left kidney to the inferior vena cava. Observe that it crosses anterior to the renal arteries and aorta.
5. Identify and clean the tributaries of the left renal vein:
o Left testicular (or ovarian) vein
o Left suprarenal vein
6. Use scissors to cut the left renal vein close to the inferior vena cava. Reflect the left renal vein toward the left. Do not detach the testicular (or ovarian) vein or the left suprarenal vein from the left renal vein.
7. Identify the left renal artery (Figure 4.45), which lies posterior to the left renal vein. Follow the left renal artery to the hilum of the kidney. The renal artery usually divides before it enters the kidney, and accessory renal arteries are common.
8. Observe small branches of the left renal artery to the ureter and left suprarenal gland.
9. Using the left renal artery as a hinge, turn the left kidney toward the right. At the most posterior part of the hilum, identify the renal pelvis and its inferior continuation, the ureter (Figure 4.46).
10. Use blunt dissection to follow the ureter inferiorly. Observe that the abdominal part of the ureter passes posterior to the testicular (or ovarian) vessels and crosses the anterior surface of the psoas major muscle (Figure 4.46). The pelvic part of the ureter will be dissected with the pelvic viscera.
11. Return the left kidney to its correct anatomical position.
12. Clean the relatively short right renal vein (Figure 4.46). Note that it has no tributaries.
13. Reflect the inferior vena cava inferiorly and slightly toward the right. Identify the right renal artery (Figure 4.45), which lies posterior to the right renal vein and inferior vena cava. Note that the right renal artery is longer than the left renal artery. The right renal pelvis lies posterior to the right renal artery.
14. Follow the right ureter inferiorly and observe its relationship to the right testicular (ovarian) vessels.
15. Use an illustration to review the relationships of the kidneys:
o The suprarenal gland is superior to the kidney.
o Through the peritoneum, the right kidney is in contact with the right colic flexure, the visceral surface of the liver, and the second part of the duodenum.
o Through the peritoneum, the left kidney is in contact with the tail of the pancreas, the left colic flexure, the stomach, and the spleen.
16. Divide the left kidney into anterior and posterior halves by splitting it longitudinally along its lateral border. Open the two halves of the kidney like a book. Identify (Figure 4.44):
o Renal capsule – a fibrous capsule that can be stripped off the surface of the kidney.
o Renal cortex – the outer zone of the kidney (about one-third of its depth).
o Renal medulla – the inner zone of the kidney consisting of renal pyramids and renal columns (about two-thirds of its depth).
o Renal sinus – the space within the kidney that is occupied by the renal pelvis, calices, vessels, nerves, and fat.
o Renal papilla – the apex of the renal pyramid that projects into a minor calyx.
o Minor calyx – a cup-like chamber that is the beginning of the extrarenal duct system. Several minor calyces combine to form a major calyx.
o Major calyx – two or three per kidney that combine to form the renal pelvis.
o Renal pelvis – the funnel-like end of the ureter that lies within the renal sinus.
o Ureter – the muscular duct that carries urine from the kidney to the urinary bladder.
IN THE CLINIC: Kidney Stones
Kidney stones (renal calculi) may form in the calyces and renal pelvis. Small kidney stones may spontaneously pass through the ureter into the bladder. Larger kidney stones may lodge at one of three natural constrictions of the ureter: (1) where the renal pelvis joins the ureter; (2) where the ureter crosses the pelvic brim; and (3) at the entrance of the ureter into the urinary bladder.
Suprarenal Glands
The suprarenal (adrenal) glands are fragile and easily torn. They are closely related to the superior poles of the kidneys (Figure 4.45). The suprarenal glands are highly vascularized endocrine glands.
1. Observe that the right suprarenal gland is triangular in shape. Part of the right suprarenal gland lies posterior to the inferior vena cava.
2. Observe that the left suprarenal gland is semilunar in shape.
3. The suprarenal gland receives multiple arteries (Figure 4.45). Identify:
o Superior suprarenal arteries arise from the inferior phrenic artery.
o Middle suprarenal artery arises from the aorta near the celiac trunk.
o Inferior suprarenal artery arises from the renal artery.
4. Note that the left suprarenal vein empties into the left renal vein. The right suprarenal vein drains directly into the inferior vena cava.
5. The suprarenal glands receive numerous sympathetic nerve fibers.
IN THE CLINIC: Suprarenal Glands
The kidneys and suprarenal glands have different embryonic origins. If the kidney fails to ascend to its normal position during development, the suprarenal gland develops in its normal position lateral to the celiac trunk.
Abdominal Aorta and Inferior Vena Cava
1. Use an illustration to study the abdominal aorta. Observe that the abdominal aorta has three types of branches (Figure 4.45):
o Unpaired arteries to the gastrointestinal tract (celiac trunk, superior mesenteric artery, and inferior mesenteric artery)
o Paired arteries to the three paired abdominal organs (suprarenal, renal, and testicular or ovarian arteries)
o Paired arteries to the abdominal wall (inferior phrenic and lumbar arteries)
2. Identify at least one lumbar artery (Figure 4.46). Four pairs of lumbar arteries supply the posterior abdominal wall. Trace one lumbar artery to its origin from the posterior aspect of the abdominal aorta. Note that the lumbar arteries pass deep to the psoas major muscle.
3. Observe the bifurcation of the abdominal aorta at vertebral level L4 (Figure 4.46). In a thin person, the umbilicus projects superior to the bifurcation of the aorta.
4. Identify the common iliac arteries, which arise at the bifurcation of the aorta. The common iliac arteries supply blood to the pelvis and lower limbs.
5. Review the inferior vena cava and its tributaries. Recall that a segment of the inferior vena cava was removed with the liver. Note that the inferior vena cava has no unpaired visceral tributaries because the hepatic portal system collects blood from the gastrointestinal tract. Review the hepatic portal vein. Recall that the hepatic portal vein drains into the liver, and that the hepatic veins drain into the inferior vena cava.
Dissection Review
1. Replace the kidneys in their correct anatomical positions.
2. Use an illustration and the dissected specimen to review the relationships of each kidney to surrounding structures.
3. Trace the path taken by a drop of urine from the renal papilla to the ureter.
4. Review the position, relationships, and blood supply of each suprarenal gland.
5. Review the branches of the abdominal aorta.
Posterior Abdominal Wall
Dissection Overview
The posterior abdominal wall is composed of the vertebral column, muscles that move the vertebral column, muscles that move the lower limb, and the diaphragm. The nerves that supply the abdominal wall and the lumbar plexus of nerves that supply the lower limb will be dissected with the posterior abdominal wall.
The order of dissection will be as follows: The branches of the lumbar plexus will be studied. Muscles that form the posterior abdominal wall will be dissected. The abdominal part of the sympathetic trunk will be studied.
Dissection Instructions
1. Move the kidney and suprarenal gland toward the midline (don't cut their vessels) and use your hands to remove the remaining fat and the renal fascia from the posterior abdominal wall.
2. Identify the psoas major muscle (Figure 4.47). The proximal attachments of the psoas major muscle are the lumbar vertebrae (bodies, intervertebral discs, and transverse processes). Its distal attachment is the lesser trochanter of the femur. The psoas major muscle is a strong flexor of the thigh and vertebral column.
3. Look for the psoas minor muscle. The psoas minor muscle is absent in approximately 40% of cases and may be present on only one side of the cadaver. The psoas minor muscle has a long flat tendon that passes down the anterior surface of the psoas major muscle to its distal attachment on the iliopubic eminence and arcuate line of the ilium.
4. Identify the iliacus muscle (Figure 4.47). The proximal attachment of the iliacus muscle is the iliac fossa. Its distal attachment is on the lesser trochanter of the femur. The iliacus muscle flexes the thigh. The iliacus and psoas major muscles form a functional unit and together they are called the iliopsoas muscle.
5. Identify the quadratus lumborum muscle (Figure 4.47). The proximal attachments of the quadratus lumborum muscle are the 12th rib and lumbar transverse processes. Its distal attachments are the iliolumbar ligament and iliac crest. The quadratus lumborum muscle flexes the vertebral column laterally and anchors the inferior end of the rib cage during respiration.
6. Review the transversus abdominis muscle. The transversus abdominis muscle forms the lateral part of the posterior abdominal wall. The transversus abdominis muscle lies posterior to the quadratus lumborum muscle.
7. Use an illustration and the dissected specimen to study the relationships between the kidneys and the posterior abdominal wall (Figure 4.46). Verify that the dorsal surface of each kidney is related, through the renal fat and fascia, to the diaphragm, psoas major muscle, quadratus lumborum muscle, and transversus abdominis muscle. The superior pole of the right kidney is at the level of the 12th rib. The superior pole of the left kidney is slightly higher, at the level of the 11th rib.
Lumbar Plexus
The nerves of the posterior abdominal wall arise from the ventral rami of spinal nerves T12 to L4. The lumbar plexus (L1 to L4) is formed within the psoas major muscle and its branches can be seen as they emerge from the lateral border of this muscle. The lumbar plexus can be seen only after removal of the psoas major muscle.
Clean the portions of the lumbar plexus nerves that lie external to psoas major muscle on both sides. On the left side only, follow each nerve proximally into the psoas major muscle, removing the muscle piece by piece (each branch of the lumbar plexus passes through the psoas major muscle at a different depth). The nerves of the lumbar plexus are variable in their branching. Use the peripheral relationships of the nerves (their region of distribution or a point of exit from the abdominal cavity) for positive identification.
1. Identify the genitofemoral nerve. It is found on the anterior surface of the psoas major muscle (Figure 4.47). It is the motor nerve to the cremaster muscle (genital part) and supplies a small area of skin inferior and medial to the inguinal ligament (genital and femoral parts). The two parts of the genitofemoral nerve divide on the anterior surface of the psoas major muscle superior to the inguinal ligament.
2. Use blunt dissection to remove the extraperitoneal fascia from the posterior abdominal wall lateral to the psoas major muscle. The branches of the lumbar plexus are in the extraperitoneal fascia and care must be taken to move the dissection instrument parallel to the course of the nerves (Figure 4.47).
3. To find the subcostal nerve, palpate rib 12 and look for the subcostal nerve about 1 cm inferior to it (Figure 4.47).
4. Find the iliohypogastric and ilioinguinal nerves (Figure 4.47). They descend steeply across the anterior surface of the quadratus lumborum muscle. Frequently, these two nerves arise from a common trunk and do not separate until they reach the transversus abdominis muscle. To positively identify the ilioinguinal nerve, follow it to the superficial inguinal ring.
5. Identify the lateral cutaneous nerve of the thigh (Figure 4.47). The lateral cutaneous nerve of the thigh passes deep to the inguinal ligament near the anterior superior iliac spine. The lateral cutaneous nerve of the thigh supplies the skin on the lateral aspect of the thigh.
6. Identify the femoral nerve (Figure 4.47). The femoral nerve lies on the lateral side of the psoas major muscle in the groove between the psoas major and iliacus muscles. The femoral nerve innervates these two muscles. The femoral nerve passes deep to the inguinal ligament and provides motor and sensory branches to the anterior thigh.
7. To find the obturator nerve (Figure 4.47), insert your finger into the extraperitoneal fascia on the medial side of the psoas major muscle and move your finger parallel to the muscle, creating a gap between the psoas major muscle and the common iliac vessels. The obturator nerve supplies motor and sensory innervation to the medial thigh.
8. Identify the lumbosacral trunk (Figure 4.47). The lumbosacral trunk is a large nerve that is formed by a contribution from the ventral ramus of L4 and all of the ventral ramus of L5. The lumbosacral trunk passes into the pelvis to join the sacral plexus.
Abdominal Part of the Sympathetic Trunk
Study the location of the sympathetic trunk on a transverse section of the abdomen (Figure 4.43). Note that the sympathetic trunk is found on the vertebral body between the crus of the diaphragm and the psoas major muscle.
1. Identify lumbar splanchnic nerves that pass anteriorly from the sympathetic trunk to the aortic autonomic nerve plexus.
2. Identify rami communicantes that pass posteriorly from the sympathetic ganglia to lumbar ventral rami. Note that each ramus communicans passes deeply between the psoas major muscle and the vertebral body. The gray rami of the lower lumbar region are the longest in the body because the sympathetic trunk crosses the anterolateral surface of the lumbar vertebral bodies.
3. Use an illustration to review the autonomic nerve supply of the abdominal viscera.
Dissection Review
1. Use the dissected specimen to review the proximal and distal attachments, as well as the action of each of the muscles of the posterior abdominal wall.
2. Review the three muscles that form the anterolateral abdominal wall (external oblique, internal oblique, and transversus abdominis).
3. Follow each branch of the lumbar plexus peripherally. Review the region of innervation of each of these nerves.
4. Use an atlas drawing to review the sympathetic trunk.
Diaphragm
Dissection Overview
The diaphragm forms the roof of the abdominal cavity and the floor of the thoracic cavity. It is the principal muscle of respiration. The diaphragm has a right half and a left half (the hemidiaphragms).
The order of dissection will be as follows: The parts of the diaphragm will be identified. The phrenic nerve will be reviewed. The greater splanchnic nerves that pass through the diaphragm will be studied.
Dissection Instructions
1. Use blunt dissection to strip the parietal peritoneum and connective tissue off the abdominal surface of the diaphragm.
2. Identify the parts of the diaphragm (Figure 4.48):
o Central tendon – the aponeurotic center of the diaphragm, which is the distal attachment of all of its muscular parts
o Sternal part – two small bundles of muscle fibers that attach to the posterior surface of the xiphoid process
o Costal part – the muscle fibers that attach to the inferior six ribs and their costal cartilages
o Lumbar part – formed by two crura (right and left)
3. Identify the right crus (Figure 4.48). The proximal attachments of the right crus of the diaphragm are the bodies of vertebrae L1 to L3. The esophageal hiatus is an opening in the right crus.
4. Observe the left crus (Figure 4.48). The proximal attachments of the left crus of the diaphragm are the bodies of vertebrae L1 to L2.
5. Identify the arcuate ligaments (Figure 4.48). The arcuate ligaments are thickenings of fascia that serve as proximal attachments for some of the muscle fibers of the diaphragm.
o Lateral arcuate ligament bridges the anterior surface of the quadratus lumborum muscle.
o Medial arcuate ligament bridges the anterior surface of the psoas major muscle.
o Median arcuate ligament (unpaired) bridges the anterior surface of the aorta at the aortic hiatus.
6. There are three large openings in the diaphragm (Figure 4.48). Identify:
o Vena caval foramen passes through the central tendon (vertebral level T8).
o Esophageal hiatus passes through the right crus (vertebral level T10).
o Aortic hiatus passes behind the diaphragm (vertebral level T12).
7. The right and left phrenic nerves innervate the diaphragm. Each phrenic nerve provides motor innervation to one half of the diaphragm (one hemidiaphragm). The phrenic nerves supply most of the sensory innervation to the abdominal (parietal peritoneum) and thoracic (parietal pleura) surfaces of the diaphragm. The pleural and peritoneal coverings of the peripheral part of the diaphragm receive sensory fibers from the lower intercostal nerves (T5 to T11) and the subcostal nerve.
8. Identify the greater splanchnic nerve in the thorax and follow it to the superior surface of the diaphragm.
9. Push a probe through the diaphragm parallel to the greater splanchnic nerve. Note that the greater splanchnic nerve penetrates the crus to enter the abdominal cavity.
10. Observe that the main portion of the greater splanchnic nerve distributes to the celiac ganglion where its sympathetic axons will synapse. The greater splanchnic nerve also innervates the suprarenal gland.
11. Find the celiac ganglia. The celiac ganglia are found on the left and right sides of the celiac trunk near its origin from the aorta. The celiac ganglia are the largest of the sympathetic ganglia that are located on the surface of the aorta.
12. Use an illustration or textbook description to review the autonomic nerve supply of the abdominal viscera.
IN THE CLINIC: Diaphragm
The phrenic nerves arise from cervical spinal cord segments (C3 to C5). Therefore, pain from the diaphragm is referred to the shoulder region (supraclavicular nerve territory).
The diaphragm is paralyzed in cases of high cervical spinal cord injuries, but is spared in low cervical spinal cord injuries. A paralyzed hemidiaphragm cannot contract (descend), so it will appear high in the thorax on a chest radiograph.
Dissection Review
1. Review the attachments of the diaphragm to the skeleton of the thoracic wall.
2. Trace the course of the thoracic aorta as it passes through the aortic hiatus to become the abdominal aorta.
3. Review the course of the esophagus and the vagus nerve trunks through the esophageal hiatus.
4. Recall the position of the heart on the superior surface of the diaphragm and review the course of the inferior vena cava.
5. Study an illustration and observe that the thoracic duct passes through the aortic hiatus and that the splanchnic nerves (greater, lesser, and least) penetrate the crura.
1. What is the vertebral level of an imaginary horizontal line drawn between the right and left iliac crests?
2. What are the structures that enter and leave the kidney along the medial border and can be elevated with it?
3. What are the anterior visceral relations of the kidneys?
4. How is the left renal vein related to the aorta, the superior mesenteric artery, and the left renal artery?
5. Where on the aorta are the origins of the renal arteries?
6. What is the developmental significance of the supernumerary (extra) renal arteries?
7. Describe the level of origin, variations, course, relations, and branches of the gonadal arteries and veins.
8. What is the relationship of the ureter to the gonadal vessels, the left colic vessels, and the root of the mesentery?
9. What is the relationship between the renal artery, the renal vein, and the renal pelvis at the hilum of the kidney?
10. What are the differences between the right and left suprarenal glands in terms of shape and relationship to the kidney?
11. What is the relationship of the right suprarenal gland to the inferior vena cava?
12. Besides the inferior phrenic vein and the suprarenal vein, what other veins drain into the left renal vein?
13. Where are the postganglionic neurons of the suprarenal glands located?
14. What is the relationship of the median, medial, and lateral arcuate ligaments to the aorta, psoas major, and quadratus lumborum muscles?
15. How are the medial and lateral arcuate ligaments formed and what are their bony attachments?
16. What is the vertebrocostal trigone and what is its significance?
17. Are there other innervations, besides the phrenic nerves, to the inferior surface of the diaphragm?
18. What are the differences in the formation and the structures transmitted by each diaphragmatic hiatus? What are the average vertebral levels of each?
19. How do the lumbar segmental arteries and the median sacral artery compare with the thoracic segmental vessels?
20. Describe the relations of the inferior vena cava to the aorta and viscera throughout the abdomen.
21. What is the significance of the location of the celiac branches of the posterior vagal trunk as they join the celiac plexus?
22. Is there a superior mesenteric ganglion around the superior mesenteric artery?
23. Is there an inferior mesenteric plexus or ganglia around the inferior mesenteric artery?
24. How does the thoracic sympathetic trunk get into the abdomen?
25. What is the source of the afferent drainage of the lumbar lymph trunks and the intestinal lymph trunk?
26. How do you distinguish between the white and gray rami communicantes?
27. How many white rami are there? Why?
28. Note the relationship between the quadratus lumborum and iliacus muscles.
29. To what group of muscles does the iliopsoas muscle belong?
30. Medial to the external iliac vein is the femoral ring. What ligaments surround it on three sides?
31. Do you find a deep inguinal node within the femoral ring?