Page 717 - The Veterinary Care of the Horse

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VetBooks.ir THE HORSE’S HEART AND THE

CIRCULATORY SYSTEM

THE CIRCULATORY SYSTEM

Blood is continuously pumped around the body by the heart. It carries gases, essential
nutrients and hormones between the various organs. The normal heart beats in a regular and

co-ordinated manner to ensure smooth and efficient passage of the blood around the body.
The heart has four chambers known as the left and right atria and ventricles (Figure 16.1).

Deoxygenated blood from the body collects in the right atrium and then flows into the right
ventricle. The ventricle pumps it through the pulmonary artery to the lungs where it takes up

more oxygen and releases carbon dioxide. The oxygenated blood from the lungs is carried by
the pulmonary vein to the left atrium and ventricle. It is pumped by the powerful left
ventricle into the aorta which branches into a network of arteries and smaller arterioles that

carry it to all the tissues of the body. The finest arterioles branch into networks of very thin
walled vessels called capillaries where gas exchange occurs. After leaving the capillary beds

in the tissues, the now deoxygenated blood is taken by veins back to the right side of the
heart. A large vein called the vena cava drains into the right atrium. From here, the blood

flows into the right ventricle and then back to the lungs. The equine heart beats on average
between 30 and 40 times per minute. To ensure maximum efficiency, it is important that

blood flows in a one-way direction. There are 4 valves which prevent the blood flowing
backwards.