Team Members: ______
Group Name: ______
Cat Dissection: Respiratory & Circulatory Systems Review
Objective: Identify & compare the gross anatomy of the cat’s respiratory & circulatory systems to that of a human’s.
Materials: The following materials should be used:
1. Embalmed cat in plastic bag & dissection tray
2. Dissecting tools (heavy duty scissors, scalpel, probe, 2 dissecting needles, forceps)
3. Name tags & String
4. Latex surgical gloves
Respiratory System Procedure: Identify the following structures in bold italics:
1. Begin your observations with the muscular diaphragm which contract in such a way as to lower the dome shaped structure during inhalation, thereby expanding the thoracic cavity above it. During exhalation the muscles relax & the diaphragm rises, decreasing the size of the thoracic cavity & forcing air out of the lungs.
2. After the diaphragm has been studied, continue to cut forward to the neck region. Begin at the diaphragm about ½ inch to the left of the midline. The ribs attach to the sternum at the midline by costal cartilages (observe them on the cat skeleton), & it will be possible to cut through these cartilages with your scissors. If you encounter too much resistance, use the bone forceps.
3. When you have cut through the first costal cartilage, open the thoracic cavity on both the right & lift sides. In the midline there are some important blood vessels which must be severed as close to the chest plate as possible.
4. Extend the incision from the thoracic cavity up the throat to the mandible. Continue the incision down the abdominal wall past the liver.
5. Make 2 cuts laterally from the midline in the region of the liver. Spread apart the thoracic walls & sever the diaphragm from the wall with scissors. The thoracic cavity may be separated into 3 parts: the pericardial cavity, into which the heart projects; the right pleural cavity, into which the right long projects; & the left pleural cavity, into which the left lung projects.
6. To enable the thoracic walls to remain open, make a shallow longitudinal cut with a scalpel along the inside surface of each side that is sufficiently deep to weaken the ribs. When the walls are folded back, the thoracic wall on each side should break at the cut.
7. Examine the larynx to identify the large flap-like epiglottis, the thyroid cartilage& the cricoid cartilage.
8. Can you find the paired vocal cords on the larynx? ______(look inside the larynx).
Trace the trachea down into the lungs. In humans the right lung has 3 lobes & the left lung has only 2.
9. The most conspicuous organs in the thoracic cavity are the lungs. Lung tissue is soft, flexible, & a dark brown color. The lungs are composed of 6 lobes: right anterior lobe, right medial lobe, right posterior lobe, left anterior lobe, left medial lobe, left posterior lobe. A seventh lobe, the mediastinal lobe on the right side, is recognized by some. The pleura is the lining of the thoracic coelomic cavity & the lung. The parietal pleura lines the cavity, which the visceral pleura covers the surfaces of the lungs.
10. Lying in the midline among the lobes of the lungs is the heart. It is surrounded by a tough sac, the pericardium.
11. Above the heart in a young cat is glandular tissue which will vary in mass in different cats. It is the thymus gland. The younger the cat, the more thymus tissue will be found. An old cat (usually with yellow fat) may have only a trace of the gland or none at all. The thymus gland has a similar fate in humans, reaching its full size in childhood.
12. Along the dorsal wall is the flattened esophagus. Follow it to the diaphragm & see where it expands to form the stomach below the diaphragm. Lying ventral to the esophagus is the trachea, supported by cartilaginous rings. At the anterior end of the trachea is the larynx, which contains the vocal cords.
13.Sitting just posterior to the larynx are the lobes of the thyroid gland, connected by a narrow isthmus. The thyroid is a reddish bi-lobed endocrine gland on the ventral side of the trachea near the larynx.
If the major blood vessels have been injected with a colored latex, the veins will be blue & the arteries will be red.
14. Insert a plastic drinking straw into the trachea & inflate the lungs. Note the great expansive capability of the lung. Can you see where the trachea branches to form the bronchi? ______Make a frontal section incision through one lung & look for further branching of the bronchus.
15. Cut into one of the lobes of a lung & note the spongy nature of the tissue. Find some of the alveoli, small air sacs with the lung.
Circulatory System Procedure:
1. Examine the pericardial sac carefully. Note that a pair of nerves attach to it laterally. These are the phrenic nerves which supply the muscle of the diaphragm.
2. Free the phrenic nerves (or at least the one the left side of the cat) from the pericardial sac. Slit the pericardial sac & fold it back out of the way.
3. The pericardium is made up of 2 membranes, one membrane is the parietal pericardium which is similar to the parietal pleura & parietal peritoneum in its formation. The visceral pericardium is not attached tot the parietal pericardium by a mesentery. The “pericardial mesentery” disappeared during the early embryonic development of the heart. The second membrane of the pericardium is a portion of the mediastinal region of the parietal pleura.
4. Identify all parts of the heart which can be seen without removing it from the body. Locate the left & right ventricles, the left & right atria (seen externally as the flap-like auricles{an auricle is a small muscular lobe from each atrium that extends posteriorly over part of the ventricle}), & the coronary artery & its branches on the surface of the heart.
5. By lifting the ventricles slightly & pulling the heart toward the cat’s left side you can see the large veins entering the right atrium. Identify the superior vena cava, which returns blood to the heart from the head & shoulders, & the inferior vena cava, which returns blood from the organs below the diaphragm. The pulmonary artery, which carries blood from the right ventricle to the lung, can be seen prominently in ventral view.
6. Remove enough connective tissue from the anterior region to expose the large aorta, which arches to the left just anterior to the heart. The pulmonary veins, which empty into the left atrium, can be seen if the ventricles are lifted & pulled the cat’s right side.
7. The heart may now be examined in more detail. Cut the pulmonary arch, the caval veins the pulmonary veins, & the aortic arch close to the heart & remove the heart. Note the stub of aortic arch remaining with the heart. With a pair of fine tip forceps loosen & then pull out the latex. This latex will be a negative impression of the semilunar valve of the aorta & will probably include the beginnings of the coronary arteries.
8. Make an incision through the wall of each atrium & cut off (transversely) the apex of the ventricles. Wash & pick out (with forceps) the clotted blood. Locate the following internal structures.
a. Coronary sinus, enters the right atrium through a small valve, near the entrance of the postcaval vein (enters the right atrium). The coronary sinus receives blood from the musculature of the heart.
b. Tricuspid valve, prevents blood in the right ventricle from entering the right atrium. There are said to be 3 flaps to this valve, but these will be very difficult to distinguish in the cat heart. The flaps are held to the walls of the right ventricle by chordae tendinae. The chordae tendinae attach to raised muscle bundles, the papillary muscles.
c. Trabeculae, are muscle bundles or strands lining the ventricles. Papillary muscles are “raised” trabeculae.
d. Pulmonary semilunar valve, between the pulmonary arch & the right ventricle. Note the 3 flaps of this valve from the ventricular side. Compare this view with the latex image of the aortic semilunar valve.
e. Aortic semilunarvalve, between the aortic arch & the left ventricle.
f. Bicuspid valve, is similar to the tricuspid valve except that it has 2 flaps rather than 3. This is sometimes called the mitral valve because of its supposed resemblance to a bishop’s mitre (cap).
Questions:
I. Trace the flow of air from the external nares to the alveoli in the lungs. (be specific)
External Nares1.
2. / (increases the surface area of the mucosa in the nose to exposed air)
3. / (most superior aspect of the pharynx)
4.
5. / (most inferior aspect of the pharynx)
6. / (also called the windpipe)
7.
8.
9.
10. / (smallest branch of the respiratory tree)
11. / (external respiration occurs in these grape-like sacs)
12. The lipid molecule that coats the alveolar surfaces is called:
13. Air moving into & out of the lungs is:
14. An emotionally induced response that is similar to crying is:
15. The total amount of exchangeable air is the:
16. The amount of air remaining in the lungs even after the most strenuous expiration is
17. Most carbon dioxide is transported in plasma as:
18. Cessation of breathing is called:
19. One of the most important stimuli leading to increased rate & depth of breathing is:
20. The bluish cast that results from inadequate oxygenation of the tissues is called:
21. Infant respiratory rate is around:
22. the condition that leads to the death of many full-term newborn infants & is still incompletely understood is:
23. Adult respiratory rate is around:
24. The interchange of gases between organisms & the environment; the taking in of O2 & the giving off of CO2:
II. Trace the pathway of blood through the heart & all body tissues.
25 / Superior & Inferior26.
27. / Valve
28.
29. / Valve
30.
31. / (external respiration occurs here)
32.
33.
34. / Valve
35.
36. / Valve
37. / (largest artery in the body)
38.
39.
40. / (internal respiration occurs here)
41.
42.
43. / Superior & Inferior