If you haven't yet dissected the coronary vessels, please do so first.
If you examined the coronary vessels on Monday, please continue on to '1. The Neck' below.
Coronary vessel dissection
a. To see the coronary vessels, use blunt dissection to remove fat and mobilize the vessels.
b. Start your dissection of the coronary arteries from the aortic valve by identifying the right, left, and posterior semilunar cusps. Appreciate the sinuses their cup- like shape creates.
c. Insert the tip of a probe into the opening of the left coronary artery in the left aortic sinus. Palpate the tip of the probe, which should now be between the aorta and the pulmonary trunk, to find the short stem of the left coronary artery.
The left coronary artery quickly divides in the coronary sulcus and forms:
The anterior interventricular (left anterior descending, LAD) artery, which descends obliquely in theanterior interventricular sulcus, supplying mainly the left ventricle and most of the interventricular septum. It then circles around the apex of the heart towards the posterior interventricular sulcus to anastomose with the posterior descending artery (a branch of the right coronary artery).
The circumflex artery, which enters the coronary (left atrioventricular) sulcus and circles around the left margin of the heart onto the diaphragmatic surface. It mainly supplies the left atrium and left ventricle.
Both the LAD and circumflex arteries are accompanied by the great cardiac vein, which becomes the enlarged coronary sinus on the diaphragmatic surface of the heart. The coronary sinus returns the blood into the right atrium via an opening medial to the IVC.
d. Find the opening of the right coronary artery in the right aortic sinus. Insert the tip of a probe into its opening and palpate the tip on the surface of the heart.
The right coronary artery runs in the coronary (right atrioventricular) sulcus, giving off branches to the sinoatrial (SA) node (circling behind the SVC) and to the chambers on either side (right atrium and right ventricle). Its main branches are:
Theright marginal branch at the inferior (acute) border of the heart, accompanied by the small cardiac vein, for the apical portions of the right ventricle.
The right coronary artery circles around the inferior border of the heart towards the diaphragmatic surface. Here it anastomoses with the circumflex of the left coronary artery. The right coronary artery also enters the posterior interventricular sulcus and gives rise to the posterior interventricular branch. It therefore supplies part of the interventricular septum as well as some of the diaphragmatic portion of the left ventricle.
The posterior interventricular branch courses along the posterior interventricular sulcus to the apex of the heart, where it anastomoses with the anterior interventricular branch of the left coronary artery. The posterior interventricular branch is accompanied by the middle cardiac vein.
The artery to the atrioventricular (AV) node also arises from the right coronary artery where the posterior interventricular sulcus meets the coronary sulcus (diaphragmatic surface).
Common variation: Note that a heart with a posterior interventricular branch from the right coronary artery is said to be "right coronary dominant." Although this is the most common pattern (about 70% of the population), sometimes the posterior interventricular artery is a branch of a larger circumflex artery (branch of the left coronary artery). In these cases, the heart is then "left coronary dominant." Try to determine if your cadaver has a right or left coronary dominant artery.
1. THE NECK
Saw through the middle of each clavicle between the insertions of the trapezius and sternocleidomastoid muscles.
Make similar cuts through any costal cartilages remaining intact above the opening cut in the thorax.
Reflect the manubrium cranially, together with the sternocleidomastoid, the sternohyoid muscles, and the medial ends of the clavicles, until the great vessels are exposed below the root of the neck.
Remove any remnants of the thymus.
Strip the pericardium from the thoracic cavity.
Identify the aortic arch and its three branches, the ligamentum arteriosum, pulmonary trunk, trachea, bronchi, superior vena cava, and brachiocephalic veins(PLAY MOVIE -courtesy of UMich)
2. PLEURAL SAC
With your hands, explore the recesses of the left and right pleural sacs or cavities.
Note that the parietal pleura extends farther caudally than the lungs on both sides.
Slip your hand down into the costodiaphragmatic recess located below the lungs and between the costal portion of the body wall and the diaphragm.
The lungs are divided externally into lobes and internally into smaller bronchopulmonary segments, the latter corresponding to the major branches of the bronchial tree inside the lung. The heart indents the left lung more deeply than the right; the left lung therefore is smaller, has only two lobes to the right's three. Each lung has 10 bronchopulmonary segments, though in the left lung some of them fuse.
Remove the lungs by transecting the pulmonary arteries and veins, the bronchi and accompanying nerves at the root (or hilum) of the lungs (PLAY MOVIE - courtesy of UMich)
Note, if visible, the tracheobronchial lymph nodes.
Examine the surface features of right and left lungs (PLAY MOVIE -courtesy of UMich)
You will want to look at and probe the two fissures on the right lung (oblique and horizontal) and the single fissure on the left (oblique)
Identify the lobes associated with those fissures. On the left lung, additionally identify the little lingula in the inferior portion.
Several thoracic organs make distinct impressions on the lung. The heart makes a deep impression on the left lung, as does the arch of the aorta and descending aorta. These features are less prominent on the right lung.
Dissect the roots of the lungs, distinguishing pulmonary veins, arteries, and primary and secondary bronchi. This will involve some gentle work with finger and probe (PLAY MOVIE -courtesy of UMich)
Note, with the aid of the figure below, the normal arrangement of veins, arteries and bronchi. These will vary a bit depending on how close to the surface of the lung you have cut.
Cut into the lung and examine the spongy tissue. Try to identify bronchi and vessels traveling through the lung tissue.
3. SYMPATHETIC TRUNK
On the right side, identify and trace the chain of paravertebral sympathetic ganglia in the thorax (PLAY MOVIE -courtesy of UMich)
Follow the sympathetic trunk and the greater splanchnic nerve, which exits the sympathetic trunk between T5-9 vertebral levels, to the diaphragm.
The sympathetic nervous system has segmental ganglia located along the sides of the vertebral bodies. These paravetebral ganglia are strung together with connecting fibers. The connected chain of ganglia is the sympathetic trunk. Sympathetic motor fibers run medially from segments of the sympathetic trunk to supply the viscera. They conjoin to form cardiac nerves (in the upper thoracic region), which run down to the autonomic plexuses near the heart, and splanchnic ("visceral") nerves (in the lower thoracic region), which pierce the diaphragm and innervate the abdominal viscera.The cardiac nerve fibers are mainly postsynaptic (their cell bodies are in the paravertebral ganglia), but the splanchnic nerve fibers are presynaptic axons. The splanchnic nerves synapse on secondary neurons located in the prevertebral or preaortic ganglia of the abdomen.
Several major structures lie dorsal to the heart. In the superior mediastinum, the esophagus and trachea run downward in contact with the vertebral bodies, with the esophagus a bit to the left of the midline. The trachea bifrucates at the carina behind the heart, and the aorta lies between the esophagus and vertebral column. The inferior vena cava, esophagus, and aorta all pierce the diaphragm with respective openings in front of the 8th (caval opening), 10th (esophageal hiatus), and 12th (aortic hiatus) thoracic vertebrae.
4. BACK TO THE MEDIASTINUM
Trace the course of the esophagus and trachea through the mediastinum.
Note their changing relationships to each other and to other mediastinal structures at various levels.
Attempt to trace some of the vagal fibers passing into the cardiac nerves and plexuses. After passing the last aortic arch derivative on each side, the vagus nerves form an esophageal plexus which coalesce to form the anterior and posterior vagal trunks on the lower esophagus.
Find the esophageal plexus and the vagal trunks on the anterior and posterior surfaces of the esophagus.
Trace the vagal plexus on the esophagus down to the diaphragm (PLAY MOVIE -courtesy of UMich)
NOTE: You will probably find the vagal fibers condensing into anterior and posterior vagal trunks, derived mostly from left and right vagus nerves respectively. Owing to the rotation of the abdominal gut, the esophagus drifts to the left and twists as it approaches the esophageal hiatus, which brings most of the right and left vagus nerve fibers into positions respectively dorsal and ventral to the gut. See figure TG 4-45 above.
Trace the inferior vena cava, esophagus, and aorta to the diaphragm.
Verify that the aorta (along with the azygos vein and thoracic duct) passes through the opening between the right and left crura of the diaphragm (aortic opening).
Verify that the esophagus, accompanied by the vagus nerves, passes through the esophageal opening in the fleshy portion of the diaphragm. The vena cava passes through the central tendon.
Note that the phrenic nerves primarily supply motor and sensory innervation to the diaphragm. However, they also send small sensory branches to the pericardium and through the diaphragm to the parietal peritoneum that covers the diaphragm's abdominal surface.
5. VENOUS AND LYMPHATIC DRAINAGE OF THE THORAX
Find the azygos vein where it empties into the superior vena cava (PLAY MOVIE -courtesy of UMich).
Follow this vein down along the posterior wall of the thorax on the right side.
Note its relationship to the aorta on the left side of the posterior wall of the thorax.
Locate midline branches of the aorta (bronchial and esophageal arteries) supplying the thoracic derivatives of the gut.
Identify several of the segmental posterior intercostal veins on the right side emptying into the azygos vein (just to the right of the esophagus).
Look to the left of the trachea and the esophagus.
Locate the left superior intercostal vein and the hemiazygos vein(s).
The venous drainage of the posterior thoracic wall is fairly variable. Typically the right and left 1st posterior intercostal veins drain directly into the posterior aspects of the right and left brachiocephalic veins respectively. Below this is the azygos venous drainage network, which is considerably more variable and asymmetric. Slightly right of the vertebral column on the posterior internal thoracic wall is the azygos vein. The azygos vein curves over the root of the lung to drain into the SVC. The hemiazygos vein on the left crosses the midline to drain into the azygos vein on the right at around the level of T8-T9.
Find the thoracic duct by looking for a thin-walled tubular structure lying between the azygos vein and the descending aorta (PLAY MOVIE -courtesy of UMich).
NOTE: The thoracic duct will seem hard to find, but if you probe carefully between the azygos and the descending aorta you will find it.
Follow the thoracic duct up toward the brachicephalic vein. It may be difficult at this stage to see its terminus.
The thoracic duct is a major lymphatic channel and it is important to be able to identify it. Lymphatics generally accompany veins. The azygos vein is accompanied by the terminal lymph channel of the body, the thoracic duct. The lower part of the thoracic duct forms from lymphatics of the right side while the upper part forms from those of the left side. It passes up the thorax, moving slightly leftward (it is variable when it crosses the midline) and typically empties into the subclavian vein near where it meets the left internal jugular vein. Its end point can vary; it can empty into the internal jugular or brachiocephalic vein directly.
1. In which direction will you reflect the manubrium and medial parts of the clavicles?
2. Where should you cut the pulmonary artery, veins, and bronchi in order to remove the lungs?
3. Will you be able to see the sympathetic trunk without removal of the parietal pleura?
Foreign body aspiration
Aspiration of foreign bodies into the lungs happens most commonly in toddlers. In general, children under the age of 15 account for 75-85% of all foreign body aspirations. In adult, this usually occurs when there is some impairment – either drug/alcohol induced, medical or mental. Aspiration in adults occurs predominantly in the right side bronchus as opposed to the left side. This is due to the nearly vertical pathway of the right bronchus and the more acute pathway of the left bronchus. The right side is also slightly wider than the left side. An object that is aspirated into the lung can cause symptoms that persist over a period of time if it is not initially discovered. Symptoms include a recurrent cough, wheezing, bronchitis, and pneumonia. The foreign body can be removed using a rigid bronchoscope.