Prosection of the Whole Abdomen and Pelvis: Abdominal Aorta & Inferior Vena Cava
- Use an illustration to study the abdominal aorta. Observe that the abdominal aorta has three types of branches:
- Unpaired arteries to the gastrointestinal tract (celiac trunk, superior mesenteric artery, and inferior mesenteric artery)
- Paired arteries to the three paired abdominal organs (suprarenal, renal, and testicular or ovarian arteries)
- Paired arteries to the abdominal wall (inferior phrenic and lumbar arteries)
- 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.
- 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.
- 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.
- Review the inferior vena cava and its tributaries. A segment of the inferior vena cava was removed with the liver.
IN THE CLINIC: Ureteric Arterial Supply
Arterial supply to the abdominal portion of the ureters arises most commonly from the renal arteries, and less commonly from the gonadal
arteries, abdominal aorta, or the common iliac arteries. The ureteric arteries are small and delicate, and may be damaged during abdominal
surgery when the ureters are retracted. Loss of the blood supply to the ureters can result in necrosis and urinary obstruction. (Source:
Clinically Oriented Anatomy, 6th Ed., p. 296).
IN THE CLINIC: Suprarenal Glands
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.
Dissection Instructions: Exploration of the Pleural Cavities
- The anterior part of the costal parietal pleura is attached to the inner surface of the removed anterior thoracic wall
- Explore the right and left pleural cavities. You may need to expand the opening in the chest wall. Caution: The cut ends of the ribs are
sharp and can cut you. To reduce the risk of injury, use a mallet or the side of the bone cutters to hit and blunt the ends of ribs 1 to 7.
As an additional precaution, place a terry cloth towel over the cut ends of the ribs before you begin to palpate the pleural cavities.
- Use a large syringe or cloth towel to remove fluid that may have collected in the pleural cavity.
- Identify the parts of the parietal pleura: costal, diaphragmatic, mediastinal, and cervical. Note that much of the mediastinal parietal pleura was removed to expose the phrenic and
vagus nerves.
- Place your fingers in the costodiaphragmatic recess. Follow it posteriorly and notice the acute angle that the diaphragm
makes with the inner surface of the thoracic wall.
- Place your hand between the lung and the mediastinum and palpate the root of the lung. At the root of the lung the
mediastinal parietal pleura is continuous with the visceral pleura. The root of the lung is attached
to the mediastinum. All other parts of the lung should slide freely against the parietal pleura. Pleural adhesions may occur between visceral
and parietal pleurae. Pleural adhesions are the result of disease processes, and you should use your fingers to break them.
IN THE CLINIC: Pleural Cavity
Under pathological conditions, the potential space of the pleural cavity may become a real space. For example, if air enters the pleural
cavity (pneumothorax), the lung collapses due to the elastic recoil of its tissue. Excess fluid may accumulate in the pleural cavity,
compress the lung, and produce breathing difficulties. The fluid could be serous fluid (plural effusion) or blood resulting from trauma
(hemothorax).
IN THE CLINIC: Pleural effusion is an abnormal accumulation of fluid in the pleural space.
Normally, only a thin layer of fluid separates the two layers of the pleura. Fluid can accumulate in the pleural space as a result of a
large number of disorders, including infections, injuries, heart failure, cirrhosis or liver failure, pneumonia, blood clots in the lung
blood vessels (pulmonary emboli), cancer and drugs. Symptoms may include difficulty breathing and chest pain, particularly when breathing
and coughing. Diagnosis is by chest x-rays, laboratory testing of the fluid, and often CT scan. Large amounts of fluid are drained with a
tube inserted into the chest.
IN THE CLINIC: Pleural Tap (Thoracocentesis)
The aspiration of pathologic material from the pleural cavity (serous fluid, fluid mixed with tumor cells, blood, pus, etc.) may be done
through the intercostal space. The pleural tap is performed in the midaxillary line or slightly posterior to it. Usually, intercostal space
6, 7, or 8 is selected for the puncture to avoid penetrating abdominal viscera. A large-bore needle is inserted (See Figure) low in the
intercostal space to avoid injury to the intercostal nerve and vessels.
Dissection Review
- Replace the anterior thoracic wall in its correct anatomical position.
- Use an illustration and the dissected specimen to project the lines of pleural reflection to the anterior thoracic wall.
- Review the course of the intercostal nerves and understand that they are the source of somatic innervation (including pain fibers) to the costal parietal pleura.
Dissection Instructions: Exposure of the Tracheal Bifurcation
- Examine the proximal stump of the root of the lung (i.e., the portion of the root that's still in the cadaver) and identify the
transected right main bronchus.
- Using blunt dissection, locate and clean the arch of the azygos vein, which passes superior to the right main bronchus to drain
into the
superior vena cava. The arch of the azygos vein and azygos system of veins will be examined in more detail during the posterior mediastinum laboratory session. Note that the right vagus nerve passes medial to the arch of the azygos vein.
- Taking care to preserve the arch of the azygos vein, dissect within the cleavage plane anterior to the main bronchus, and follow it
proximally to expose the tracheal bifurcation. Clear the connective tissue around the tracheal bifurcation until you can clearly identify
the trachea, and right and left main bronchi.
- Locate the deep part of the cardiac plexus lying anterior to the tracheal bifurcation.
- Observe that tracheobronchial lymph nodes are located around the trachea near its bifurcation.
- Compare the right and left main bronchi. Observe that the right main bronchus is larger in diameter, shorter, and oriented more
vertically than the left main bronchus.
- Place the breast plate back onto the cadaver. Note that the trachea bifurcates within or close to the horizontal plane passing through
the sternal angle.
- Palpate the anterior and posterior surfaces of the trachea near its bifurcation. Observe that the tracheal rings are C-shaped and that
the open part of the "C" is located posteriorly.
- Observe that the esophagus is located posterior to the trachea in close relationship to the open part of the tracheal cartilages.
- Use scissors to make a longitudinal cut through the anterior surface of the right and left main bronchi
(See Figure, dashed lines). The cuts should meet anterior to the tracheal bifurcation. Make a third cut
superiorly through the anterior surface of the trachea for a distance of 2.5 cm. Inside the tracheal bifurcation, identify the carina
(L. carina, keel of a boat). The carina is a specialized piece of tracheal cartilage. Because the trachea and bronchi are rigid,
reflection is sometimes difficult. If necessary, you can cut out a small window through the anterior wall of the trachea and/or bronchus
to help you see the carina.
- Place the lungs back into the cadaver.
IN THE CLINIC: Bifurcation of the Trachea
During bronchoscopy, the carina serves as an important landmark because it lies between the superior ends of the right and left main bronchi.
The carina is usually positioned slightly to the left of the median plane of the trachea. When foreign bodies are aspirated, they usually
enter the right main bronchus because of the leftward position of the carina, and because of the fact that the right main bronchus is wider
and more vertically oriented than the left main bronchus.
Dissection Review
- Review the parts of the lungs.
- Replace the lungs in their correct anatomical positions within the thoracic cavity.
- Replace the anterior thoracic wall. Review the relationship of the pleural reflections to the thoracic wall.
- Review the costomediastinal and costodiaphragmatic recesses.