FOCUS QUESTIONS and ANSWERS:

1. Are there plexuses of nerves on the pulmonary arteries? 

The pulmonary plexuses lie around the roots of the lungs, and the pulmonary artery is one of the structures of the lung roots. Therefore, there are plexuses on the arteries.

2. Determine the relation of the left superior intercostal vein to the aortic arch, the phrenic nerve, and vagus nerves.

The left superior intercostal vein runs between the vagus and phrenic nerves. It crosses the aortic arch horizontally passing from the heads of the ribs anteriorly to end in the left brachiocephalic vein.

3. Pull the aortic arch toward the left and observe the thoracic portion of the trachea. What innervates it and how?

The recurrent laryngeal nerves innervate the upper trachea and esophagus as they pass superiorly in the tracheoesophageal groove to reach the larynx, which they also innervate. Recurrent laryngeal nerves provide skeletal motor innervation to the voluntary muscle of upper esophagus and larynx and parasympathetic motor innervation to the smooth muscle of the trachea. They also provide parasympathetic motor innervation to the mucous glands of all of these structures.

4. What is the blood supply of the trachea? What structure does it lie upon?

For the blood supply, see above. The trachea lies upon the esophagus.

5. Locate the right and left bronchial arteries. What is their source? How do the two sides differ in number?

The two left bronchial arteries are branches from the highest part of descending aorta. The single right bronchial artery is either a branch of one of the left bronchial arteries or it may branch from the right 3rd posterior intercostal artery, in which case the common trunk is called the intercostobronchial trunk.

6. What is the difference between the "root" of the lung and the "hilum"?

The root of the lung is the collection of structures that connect the lung to the mediastinum. This includes the pulmonary arteries and veins, the primary bronchi and bronchial arteries, and the pulmonary nerve plexuses and lymphatics. The hilum is the place on the lung where these structures enter and leave the lung.

7. How do the cardiac and pulmonary plexuses differ? Where do they distribute?

The cardiac and pulmonary plexuses are continuous at the tracheal bifurcation. The heart receives the cardiac plexus and lungs the pulmonary plexus.

8. Where and what is the cardiac notch? 

The cardiac notch is a lateral deviation in the anterior border of the left lung, caused by the position of the heart. The lingula is an anterior projection of the left superior lobe below the cardiac notch.

9. What is the average projection of each lung and its fissures to the rib cage?

The anterior borders of each lung generally follow the sternal margin, although the cardiac notch causes a lateral deviation to the left anterior border between the 4th and 6th ribs. The apex of each lung projects to the level of T1, which means, due to the declination of the first rib anteriorly, that the apex rises above the first rib. The inferior border of each lung is located at rib 6 in the midclavicular line, rib 8 at midaxillary line, and rib 10 in the paravertebral line. (Recall that the pleura goes 8, 10, 12.) Both oblique fissures begin posteriorly at the spine of T3, passing obliquely (like the name implies) to reach the 6th costal cartilage near the midclavicular line. The horizontal fissure of the right lung begins at rib 5 in the midaxillary line, then reaches rib 4 to follow it anteriorly to the sternal margin.

10. What is the lingular bronchus?

The left superior lobe bronchus has two divisions: superior and lingular. The lingular division or lingular bronchus has two segmental bronchi: superior lingular and inferior lingular.

11. What is its significance of the superior segmental branch of the right inferior lobar bronchus?

Due to its larger caliber and more vertical orientation, the right primary bronchus is more likely to receive foreign bodies that enter the airway. The superior segmental bronchus branches posteriorly off of the intermediate bronchus or the inferior lobe bronchus, so it is the most likely segmental bronchus to receive those foreign bodies that enter the right bronchus. This is especially true if the patient is in a supine position.

12. Are there sympathetic branches to the lung? Along what do they distribute?

Sympathetic fibers reach the lungs via the pulmonary plexuses, which are located along the roots of the lungs. Pulmonary plexuses are continuous with the cardiac plexus at the tracheal bifurcation. Additional sympathetics reach the pulmonary plexuses via the thoracic visceral nerves, which are branches from T1-T4/T5 sympathetic chain ganglia.

13. Where does the esophagus begin? Where does it pass into the abdomen? Where does it terminate?

The laryngopharynx "becomes" the esophagus at the C6 level. The esophagus passes through the esophageal hiatus of the diaphragm, which is at the T10 level, to end in the cardiac portion of the stomach.

14. Consider the course, relations, constrictions of the esophagus. 

For course and relations, see above. Constrictions of the esophagus are found at its beginning, at the tracheal bifurcation, and at the esophageal hiatus.

15. Describe the blood supply and venous drainage of the esophagus. Are there venous collaterals to stomach?

Two or three esophageal arteries branch from the descending aorta. Esophageal veins drain into the azygos system, which eventually reaches the superior vena cava. The esophageal tributaries of the left gastric vein drain the terminal esophagus. Since the gastric veins first drain into the portal system before going to the heart, this part of the esophagus is an important site of portal-caval (portal-systemic) anastomosis in cases of portal hypertension.

16. Do the right and left mediastinal pleurae come together?

Very low in the posterior mediastinum the esophagus sweeps forward, so there is potential for the right and left mediastinal parietal pleurae to touch one another posterior to esophagus and anterior to aorta. However, typically the anterior deviation of the esophagus is not sufficient to allow enough space for this contact of the pleurae.

17. Through what and at what level does the aorta enter the abdominal cavity?

The descending thoracic aorta passes through the diaphragm at the aortic hiatus, a passageway between the two diaphragmatic crura, located at the T12 level.

18. What is the subcostal artery?

Below the 12th rib, there is no intercostal space or intercostal artery, so we call the segmental neurovascular structures subcostal.

19. Completely review the blood supply to an intercostal space.

Intercostal spaces in general are supplied by posterior and anterior intercostal arteries. Posterior intercostal arteries 3 through 11 are branches of the descending thoracic aorta. The first two posterior intercostal arteries are branches of the highest intercostal artery, which is a branch of the costocervical trunk from subclavian artery. Anterior intercostals are branches of the internal thoracic or the musculophrenic arteries.

20. What are the posterior branches of the posterior intercostal (segmental) arteries? What do they supply?

The posterior branches of posterior intercostal arteries supply the deep and superficial back muscles, skin of the back, and the vertebral column. They have radicular branches that reach the spinal cord along the dorsal and ventral rootlets.

21. Observe the azygos venous system. If you have two primary veins, do they communicate with one another? How? Where? What is the pattern of venous drainage in your specimen? Are all the veins present? If not, where does the drainage go?

Hemiazygos and accessory hemiazygos usually cross the midline at T7, 8, or 9 to empty into the azygos vein. There are also connections between the various left-sided venous channels.

22. What vein drains the first intercostal space? Into what does it drain? What veins drain into the azygos system?

Both first posterior intercostal veins drain directly into their respective brachiocephalic veins. Bronchial and esophageal veins drain into the azygos system, the latter being a significant site of portal-caval anastomosis in cases of portal hypertension. (This is the second mention... could be important!)

23. How does the thoracic duct get into the thorax? At what level does it deviate to the left side?

The thoracic duct enters the chest through the aortic hiatus along the right side of the aorta. It deviates to the left at the level of the sternal angle. (The trachea pushes the esophagus against the vertebral bodies which pushes thoracic duct to the left.)

24. Do you find posterior mediastinal lymph nodes or afferent lymph channels?

The thoracic duct is usually paralleled by posterior mediastinal nodes.

25. What are bronchomediastinal lymph trunks?

The lymph from the lungs and chest passes through the paratracheal nodes to form the bronchomediastinal lymph trunks. These drain to the thoracic duct on the left and the right lymphatic duct on the right.

26. Is the sympathetic trunk located within the posterior mediastinum? Does it change positions in different regions of the chest?

The sympathetic trunk lies on the heads of the ribs through most of the chest, so it is almost, but not quite, within the posterior mediastinum. It deviates anteromedially as it travels inferiorly to its exit through the diaphragm.

27. How many thoracic ganglia do you find?

There are typically 12 thoracic ganglia, although the first may be fused with the inferior cervical ganglion to form a cervicothoracic (stellate) ganglion.

28. Identify white and gray rami communicans. What is their significance and distribution? What do they contain?

Since the preganglionic sympathetic neurons live within the spinal cord at T1 to L2 levels, these are the only levels where white rami communicans are found. Gray rami, on the other hand, are found at every level at which there are spinal nerves. Gray rami carry postganglionic sympathetic fibers back to the ventral primary rami, to be distributed along their branches (and also the branches of the dorsal primary rami).

29. Do you see thoracic visceral nerves to the aorta, esophagus, and trachea? What about to the cardiac and pulmonary plexuses?

The first 4 or 5 thoracic ganglia (T1-4) give small visceral branches that pass anteroinferiorly to reach the cardiac, pulmonary, esophageal, and aortic plexuses, as well as the trachea.

30. Expose the greater (thoracic) splanchnic nerve. From what does it come? At what level? What types of fibers does it contain? To what does it distribute?

The greater thoracic splanchnic nerve is made by contributions from sympathetic chain ganglia at T5 to T9 (or T10) levels. These are preganglionic fibers that leave the chest to enter the abdomen. They synapse in the celiac ganglion and innervate the abdominal viscera that is supplied by the celiac trunk.