Prelab Images - Superior Mediastinum & Lungs

Prelab Images - Superior Mediastinum & Lungs

Prelab should consist of reading the lab manual and dissector answers and viewing the dissection video. To begin your study, you may find it useful to look over the Netter's Atlas images listed below.
Step 1. Define the boundaries of the superior mediastinum and peel away the mediastinal pleura. (Play movie)
Plate 231 shows the superior mediastinum (the boundaries are the superior thoracic aperture superiorly, the plane through the sternal angle and T4/T5 inferiorly, the sternum anteriorly, the spinal column posteriorly, and the mediastinal pleura laterally). Remove the mediastinal pleura from any structures it may be covering in the superior mediastinum. Plate 198 shows the course of the phrenic nerve and that this nerve is accompanied by the pericardiacophrenic atery and vein (which are cut in this plate). Plate 191 shows the pericardiacophrenic artery branching from the internal thoracic artery.
Step 2. Strip the pericardium from the thoracic cavity and identify the parts of the aortic arch, ligamentum arteriosum, pulmonary trunk, trachea, and bronchi. (Play movie)
Next, remove the pericardium to expose the great vessels, bifurcation of the trachea, and the esophagus. Plates 210 and 236 show the structures that you need to identify and their relations to each other. Plate 199 shows the hilum of the lung. It is important to note that the pulmonary veins emerge from the hilum of the lung anteriorly to the pulmonary arteries and bronchi. Plates 206, 212, and 199 can also be used to trace the pulmonary arteries to the hilum of the lung. Plates 206 and 212 label the ligamentum arteriosum. Plate 209 labels the anterior and posterior pulmonary plexuses, which will be on the pulmonary arteries at the hilum of the lung.
Step 3. Remove the lungs. (Play movie)
Plates 206 and 232 show the tracheal bifurcation and the relation of the main bronchi to the arch of the aorta, the esophagus, the azygos vein, and the pulmonary arteries. Plate 209 shows the right and left vagus nerves moving behind the main bronchi. Next, cut through the main bronchi, the pulmonary arteries, and the pulmonary veins at the hilum of the lung and remove the lung. You can now see where the pulmonary arteries and veins and the bronchi enter or exit at the hilum of the lung (like in plate 199).
Step 4. Clean and dissect the structures of the superior mediastinum, including the great vessels and remnants of the thymus. (Play movie)
Plate 212 shows the junction of the internal jugular and subclavian veins to form the right and left brachiocephalic veins. You should have elevated the sternocleidomastoid and strap (sternohyoid and sternothyroid) muscles in an earlier lab, but you may need to elevate them more to see the brachiocephalic veins (plates 31 and 32 for the mentioned neck muscles). Plate 212 labels the right and left brachiocephalic veins. Plate 211 shows the thymic fat, which will have veins embedded within it that drain into the left brachiocephalic vein. Plate 74 shows the inferior thyroid veins. Plates 212 and 191 label the internal thoracic vein. Plate 231 shows the left superior intercostal vein as it passes between the phrenic and vagus nerves on the arch of the aorta. Plate 212 labels the superior vena cava and its position beneath the manubrium can be appreciated in plate 196. Plate 230 shows the azygos vein entering the superior vena cava on the right side. Plate 238 shows the azygos system, which will be dissected in step 8. Looking at plate 212, cut through the midpoint of the left brachiocephalic vein so you can better see the underlying vagus nerve. Plates 209 and 240 follow the vagus nerve and show it giving off cardiac branches. Plates 232 and 237 identify the major branches off the arch of the aorta: the brachiocephalic trunk, the left common carotid, and the left subclavian arteries. The vertebral artery is usually a branch off the sublclavian artery (plate 33, bottom), but sometimes the left vertebral artery will branch from the aortic arch. Plate 239 shows a couple lymph nodes laying on the left brachiocephalic vein. These would be considered anterior mediastinal lymph nodes, but they are not labeled. The boundaries of the posterior mediastinum can be seen in plate 231 and are written in objective 5. Plates 185 and 196 show the vertebrae and ribs forming the thoracic wall.
Step 5. Explore the tracheal bifurcation and the main (primary) bronchi. (Play movie)
Plates 202 and 232 show the trachea. Plates 209 and 240 show the trachea receiving its innervation from the vagus nerve (parasympathetic) and the sympathetic trunk (sympathetic). Plate 207 shows the right and left bronchial arteries coming from the aorta. The trachea also receives blood from the internal thoracic and inferior thyroid arteries (both shown in plate 33). The inferior thyroid vein (74) drains the trachea. The inferior thyroid artery and vein will be seen more in later labs. Plate 202 shows the trachea branching into left and right main bronchi. If you cut the trachea open you will find a small piece of cartilage known as the carina at the point of bifurcation. Plate 202 shows the right and left main bronchi by themselves. Plates 206, 230, 231, and 232 show the relations of the bronchi to the other structures of the thoracic cavity. Plate 199 shows the relation of the bronchi to the other structures at the root of the lung (Note: the pulmonary veins enter the anterior portion of each lung). Plates 209 and 240 show the cardiac and pulmonary plexuses.
Step 6. Examine the surfaces and hilum of the lung. Identify the lymph nodes involved in lymphatic drainage of the lungs. (Play movie)
Plate 199 shows the apex, base, surfaces, borders, lobes, and fissure of each lung. This plate also labels the cardiac notch of the left lung. Plates 196, 197, and 196 show the surface projections of the lung to the rib cage. Plate 199 shows the visceral pleura covering the lung reflecting at the hilum. This reflection forms the pulmonary ligament (199). After the reflection the pleura becomes parietal pleura and lines the thoracic cavity (198). Dissect the structures at the hilum and note their relationship to one another (199).
Step 7. Dissect the bronchi, defining the lobar branches. (Play movie)
Plate 203 shows the lobar (secondary) bronchi. Plate 205 shows that the pulmonary artery follows the lobar bronchi (it follows the pathway that air takes all the way to the alveolus). Plate 199 identifies the lingula, plates 202 and 203 label the lingular bronchus, and plate 201 shows the area of the lung supplied with air by the lingular bronchus. The segmental (tertiary) bronchi and bronchopulmonary segments of each lung are shown in plates 203 and 197. Dissect the superior segmental (tertiary) bronchi of the right inferior lobar bronchus (labeled B6 in plate 203). Follow the intermediate bronchus downward by using a probe to remove the lung tissue. Near the point where it divides into middle and inferior lobar bronchi you will see the superior segmental bronchus branching off posteriorly. Plate 205 once again shows that the pulmonary artery will follow the bronchi, while the pulmonary vein is in an intersegmental plane.

Plate 208 shows the lymphatic drainage of the lung. You may also want to check out plate 195 for the muscles of respiration and plate 204 for a schema of the intrapulmonary pathway because these topics may be important.