Circulatory Physiology

Anatomy of the Sheep Heart

Although you have already examined the heart of your fetal pig, you will also study the sheep heart, since it is larger and many structures are easier to see. As you examine the heart you should keep in mind the pattern of blood flow through it. Remember that deoxygenated blood returning from the body enters the right atrium via the anterior vena cava and posterior vena cava.

From the right atrium blood passes into the right ventricle, and from there to the lungs via the pulmonary artery. After being oxygenated in the lungs, blood returns to the left atrium via the pulmonary veins. From the left atrium it enters the left ventricle, and is pumped out to the body via the aorta.

Begin by observing an intact heart. The narrow, pointed end is the apex, or posterior end of the heart. Notice that the heart is very muscular in this area because the ventricles are located at this end of the heart. The wider end, from which the blood vessels arise and enter, is the base (not labeled), or anterior end. The image to the right shows the ventral surface of the heart. It can be identified by the prominent groove, the interventricular sulcus. This groove marks the division between the left ventricle (on your right as you look at the ventral surface and the right ventricle (on your left as you look at the ventral surface). Two large vessels spring from the base of the heart on the ventral surface. These large vessels are the aorta (not visible in this image) and the pulmonary artery. The pulmonary artery leaves the heart slightly to the left of and ventral to the aorta. To the right of the two large arteries locate the thin-walled left atrium. To the left of these arteries locate the right atrium. Each atrium bears a thin-walled flap or appendage, the auricle.