LAB 10 Thoracic Viscera
Lungs and Heart
Lab Objectives:
• Remove the lungs but leave the heart and other mediastinal viscera in situ.
• Study the isolated lungs noting the lobes, lobules, bronchi and vessels. Note the well defined interlobular septa in bovine and porcine lungs but not in ovine or equine lungs.
• Identify the vagus and phrenic nerves and their branches as they pass through the mediastinum. Adjacent to the vertebrae note the sympathetic nerve trunk and ganglia.
• Identify the vessels of the mediastinum including azygous veins, caval veins, aorta and branches, coronary arteries and branches of the brachiocephalic trunk. Attempt to find the thoracic duct. On the equine heart note both branches of the left coronary artery and trace the strong right coronary artery to the subsinuosal groove. This will require removal of fat from the coronary groove on both sides.
• Identify mediastinal lymphoid structures including the thymus, tracheobronchial nodes and the large caudal medastinal lymph node in ruminants.
• On isolated unfixed hearts identify the four valves and their parts. In the right heart note the coronary sinus, intervenous crest and trabecula septomarginalis.
Anatomical Terms:
Thorax Structures (continued)
(thymus)
esophagus
diaphragm:
central tendon
diaphragmatic crura
aortic hiatus
esophageal hiatus
Thoracic Vessels and Nerves (continued)
sympathetic trunk
dorsal vagal nerve trunk
ventral vagal nerve trunk
phrenic n.
thoracic duct
right azygous v.
left azygous v. (bov, por)
caudal vena cava
cranial vena cava
great cardiac v.
coronary sinus
brachiocephalic v.
external jugular v.
internal jugular v. (bov, por)
pulmonary vv.
aorta:
left coronary a.
circumflex branch
subsinusoidal a. (bov)
paraconal branch
right coronary a.
subsinuosal a. (eq, por)
aortic arch
brachiocephalic trunk
right &left subclavian aa.
internal thoracic a.
superficial cervical a.
costocervical a.
vertebral a.
axillary a.
bicarotid trunk
right common carotid a.
left common carotid a.
Heart Structures
coronary groove
right atrium
right auricle
coronary sinus
intervenous tubercle
terminal crest (crista terminalis)
right AV valve (tricuspid)
chordae tendinae
papillary m.
right ventricle
trabecula septomarginalis
conus arteriosus
pulmonary semilunar valve
pulmonary trunk
pulmonary arteries
left atrium
left auricle
pulmonary vv.
left AV (mitral) valve
left ventricle
chordae tendineae
papillary m.
Instructor Commentary:
Pluck is a collective lay term for the heart, lungs and thoracic esophagus which are "plucked" out of the carcass during slaughter. The heart and major vessels lie in the mediastinum which is exposed in the cadaver by removal of the lungs. The apex of heart always belongs to the left ventricle. External separation of the ventricles is marked by a paraconal groove on the left side and a subsinuosal groove on the right side. The ventricles are separated from the atria by the coronary groove. All of these grooves are fat filled so that the coronary vessels which lie in the grooves are often obscured. The right coronary artery is well developed in the horse and pig while the left coronary a. is favored in carnivores and ruminants.
A zygote is a pair. Azygous means unpaired. This term is used to refer to the vein that drains most of the thoracic wall. In development there is a pair of veins that becomes unpaired after one is lost except in ruminants which have right and left azygous veins. Most species have a right azygous vein but the pig has a left azygous vein. Camelids differ from ruminants in having an azygous vein on the right side only. The right azygous v. empties directly into the right atrium but the left azygous v. empties into the coronary sinus which in turn empties into the right atrium.
Roaring is a common term for laryngeal hemiplegia which refers to paralysis (plegia) on one side (hemi) of the larynx. In most cases the larynx is paralyzed on the left side. This predilection can be explained by right/left differences in the path of the recurrent laryngeal nerve in the thorax. On the left side the recurrent laryngeal nerve passes around the ligamentum arteriosum and the aorta but on the right side the recurrent laryngeal nerve loops around the subclavian artery. On the left side the recurrent nerve passes close to the left tracheobronchial lymph nodes but on the right side the recurrent loop is cranial to the tracheobronchial lymph nodes. Damage to the recurrent nerve may be due to spread of inflammatory substances from inflamed left tracheobronchial lymph nodes to the adjacent left recurrent nerve (image 10-4).
Cattle have a pair of os cordis bones at the base of the aorta. These are not found in small ruminants or horses.
Typically the trachea terminates by bifurcating into two primary bronchi. In ruminants and pigs there is a third primary bronchus that arises on the right side cranial to the tracheal bifurcation. This third bronchus is called the tracheal bronchus which is an unfortunate term because the bronchi at the bifurcation are also tracheal bronchi.
Red latex under pressure passes in a reverse direction of normal flow as it passes from the carotid a. to the aorta and then to the left heart and pulmonary veins. Blue latex passes in the normal flow direction from the jugular v. to the cranial vena cava and then to the right heart and pulmonary arteries. These facts can be used to identify vessels associated with the lungs (image 10-4).
Dissection Images:
Note: Click an image to see it enlarged, view its caption, and toggle its labels.
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