Exploring the Pig Heart


 The pig heart, like that of other mammals, has four chambers. Each chamber is joined to a large blood vessel. A valve is present between each upper and lower chamber and between each lower chamber and the blood vessel exiting it. The heart in the adjoining photograph (anterior view) has been removed from the pericardium which surrounds it when it is in the body. The blood vessels have also, unfortunately, been cut very close to where they enter and leave the heart.

Notice the crown of fat that runs horizontally across and around the heart. Notice also the blood vessels within the fat. The upper edge of this fatty layer marks the boundary between the heart's upper and lower chambers. Another ring of fat runs diagonally across the heart. This ring marks the boundary between the right and left sides of the heart.

As you observe the next series of photographs remember that what you see in the photograph is left-right reversed. To see a photograph of the structure click on its name. To return to this narrative after examining the photograph click on BACK.

The right atrium is one of the receiving chambers of the heart. It is thin walled, small in comparison to a ventricle and resembles the shape of an ear. Blood flows into the right atrium from the vena cava. This vein carries blood from the body back to the heart. The photograph shows the opening in the posterior wall of the atrium where the vena cava is attached. The right ventricle is located under the right atrium. This ventricle is large, thick walled and covered by surface fat deposits .

Blood flows from the right atrium into the right ventricle through the right AV valve. After the ventricle fills with blood it contracts and then the AV valve closes preventing backflow into the atrium. With backflow prevented, the blood is forced to move onward through the pulmonary semilunar valve and into the pulmonary artery. The forceps in the photograph extends from the upper region of the ventricle through the valve and into the pulmonary artery. The pulmonary artery carries blood deficient in oxygen and rich in carbon dioxide to the lungs. This blood vessel divides once in order to reach each lung. As blood passes through the lungs carbon dioxide is released and a new supply of oxygen enters the blood and immediately combines with hemoglobin. In the lung smaller blood vessels recombine to form a large pulmonary vein that returns the blood to the left atrium. This is the only vein in the body that transports blood rich in oxygen. The left atrium collects blood returning from both lungs. It is also thin walled and small when compared to a ventricle. After filling, the atrium contracts forcing blood through the open left AV valve and into the left ventricle. The left AV valve, like the one on the other side of the heart, prevents backflow of blood when the ventricle contracts. The left ventricle is the largest and most muscular heart chamber. When it contracts blood is forced under very high pressure out through the aortic semilunar valve and into the aorta. This blood vessel, the largest of all of the arteries, branches into a network of smaller arteries that transport blood to all parts of the body.

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