The general structure of the circulatory system of the rat is almost identical to that of humans. Pulmonary circulation carries blood through the lungs for oxygenation and then back to the heart. Systemic circulation moves blood through the body after it has left the heart. You will begin your dissection at the heart. It is important that you do not cut the vessels as you carefully remove any muscles and surrounding tissue to expose them. Your rat should be double injected so that arteries and veins are visible as blue and pink.
The heart of the rat is too small to view many of the structures listed below. Use models of human hearts or images in the dissection guides to identify the structures and label them on the diagram.
1. Blood from the posterior
portion of the body enters the right atrium of the heart through the inferior
vena cava and the superior vena cava.
2. Blood flows from the right atrium to the right ventricle via the tricuspid valve.
3. Blood is then pumped through the pulmonary semilunar valve and into the pulmonary trunk where blood travels to the lungs.
4. Blood then flows through the pulmonary arteries to the lungs where it is oxygenated and then returns from the lungs to enter the left atrium via four pulmonary veins. Only one of these is visible on the diagram, a tiny vessel on the right side.
5. Blood goes from the left atrium to the left ventricle via the bicuspid (or mitral) valve.
6. Blood leaves the left ventricle of the heart through the aortic semilunar valve and enters the aorta. The aorta has a visible arch with vessels that lead to the head before the artery descends into the rat's thoracic cavity.
Label the diagram using the descriptions and bold words. Trace the flow of blood using arrows.
Branches of the Aorta
The aorta has four general areas. Locate each of these on your rat.
ascending aorta - the upper part of the vessel that starts at the atrium
aortic arch - the place where the aorta bends to the left.
descending aorta - after the bend, the aorta can be traced toward the diaphragm
abdominal aorta - the aorta passes through the diaphragm and supplies blood to the lower extremities
1. Coronary arteries
are located on top of the heart and supply the heart itself with blood.
2. The first visible branch from the aorta is the brachiocephalic artery, it divides into the right common carotid artery, which supplies the right side of the neck, and the right subclavian artery, which supplies the right shoulder and arms. Locate the carotid arteries on your rat, they will be obvious arteries that travel up the side of the next.
3. At the most anterior part of the bend in the aortic arch is the left common carotid artery, which supplies blood up the left side of the neck. If you are careful you can follow the common carotid to where it branches into the internal and external carotid.
4. Immediately to the left of the left common carotid artery is the left subclavian artery, which supplies blood to the left shoulder and arm. The sublclavian artery becomes the axillary artery as it enters the forearm.
Procedure: Carefully tease away the muscles and tissue so that the subclavian, the axillary and the right common carotid can be seen.
Many of the arteries that branch from the aorta in this part of the rat are small and fragile. You may not be able to find all of them, but with careful dissection a few can be exposed. They are often named for the organ or structure the vessel supplies blood to. Find at least three of the vessels listed for your checkpoint. If you cannot find the vessel, do not check the box.
1. The first arterial branch from the abdominal
aorta (below the diaphragm) is the celiac artery which branches to arteries
that supply the stomach (gastric artery), liver (hepatic artery),
spleen and pancreas (splenic artery) .
2. The second artery arising from the abdominal artery is the superior mesenteric artery, which is larger than the celiac, and delivers blood directly to the small intestine.
3. The renal arteries are short and lead directly to the kidneys. These are probably the easiest to locate.
4. Just posterior to the renal arteries are the genital arteries, which lead to the testes or the ovaries.
5. Farther along the abdominal aorta, you can find the iliolumbar arteries which lead to the dorsal muscles of the back.
6. Next, the inferior mesenteric artery leads to the intestinal mesenteries.
7. The abdominal aorta gives rise to the caudal artery, which goes on into the tail.
8. The abdominal aorta finally divides to form the iliac arteries, which deliver blood to the pelvis and hind legs.
9. The iliac arteries lead to the femoral artery in the leg.
Procedure:Attempt to locate the vessels above, find at least three of them.
1. The left and right
superior vena cava conduct blood from the upper part of the body into the
right atrium. Trace these veins from the atrium until you find the small internal
jugular vein and continues as the subclavian vein.
2. The subclavian vein divides into the external jugular vein and the axillary vein.
3. The inferior vena cava carries blood from the lower part of the body to the right atrium. The hepatic vein drains the liver and enters the inferior vena cava near the diaphragm.
4. Renal veins drain the kidneys.
5. Genital veins lead from the gonads and enter the inferior vena cava.
6. The iliac and femoral veins drain the legs.
7. The caudal vein drains the tail.
Procedure: Expose the inferior vena cava and the area where it branches into the femoral and caudal veins.