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The Heart

Categories: Circulatory System

The heart is the central organ of the entire system and
consists of a hollow muscle; by its contraction the blood is pumped to all

parts of the body through a complicated series of tubes, termed arteries.

The arteries undergo enormous ramifications (branchings) in their course

throughout the body and end in very minute vessels, called arterioles,

which in their turn open into a close meshed network of microscopic (very

vessels, termed capillaries. After the blood has passed through

the capillaries it is collected into a series of larger vessels called

veins by which it is returned to the heart. The passage of the blood

through the heart and blood vessels constitutes what is termed the

circulation of the blood. The human heart is divided by a septum

(partition) into two halves, right and left, each half being further

constricted into, two cavities, the upper of the two being termed the

auricle and the lower the ventricle. The heart consists of four chambers

or cavities, two forming the right half, the right auricle and right

ventricle, and two forming the left half, the left auricle and left

ventricle. The right half of the heart contains the venous or impure

blood; the left the arterial or pure blood. From the cavity of the left

ventricle the pure blood is carried into a large artery, the aorta,

through the numerous branches of which it is distributed to all parts of

the body, with the exception of the lungs. In its passage through the

capillaries of the body the blood gives up to the tissues the material

necessary for their growth and nourishment and at the same time receives

from the tissues the waste products resulting from their metabolism, that

is, the building up and tearing down of the tissues, and in so doing

becomes changed from arterial or pure blood into venous or impure blood,

which is collected by the veins and through them returned to the right

auricle of the heart.

From this cavity the impure blood passes into the right ventricle from

which it is conveyed through the pulmonary (lung) arteries to the lungs.

In the capillaries of the lungs it again becomes arterialized by the air

that fills the lungs and is then carried to the left auricle by the

pulmonary veins. From this cavity it passes into that of the left

ventricle, from which the cycle once more begins. The heart, then, is a

hollow muscular organ of a conical form, placed between the lungs and

enclosed in the cavity of the pericardium. It is placed obliquely in the

chest. The broad attached end or base is directed upwards, backwards and

to the right and extends up to the right as high as the second rib and the

center of the base lies near the surface underneath the breast bone. The

apex (point) is directed downwards, forward and to the left and

corresponds to the space between the cartilage of the fifth and sixth

ribs, three-fourths of an inch to the inner side, and one and one-half

inches below the nipple, or about three and one-half inches from the

middle line of the breast bone. The heart is placed behind the lower two-

thirds of the breast bone and extends from the median line three inches to

the left half of the cavity of the chest and one and one-half inches to

the right half of the cavity of the chest.

Size: In adults it is five inches long, three and one-half inches in

breadth at its broadest part and two and one-half inches in thickness.

Weight in the male ten to twelve ounces; in the female eight to ten. It

increases up to an advanced period of life. The tricuspid valve (three

segments) closes the opening between the right auricle and right

ventricle. Pulmonary semilunar valves guard the orifice of the pulmonary

artery, keeping the blood from flowing back into the right ventricle. The

mitral valve guards the opening to the left ventricle from the left

auricle. The semilunar valves surround the opening from the left ventricle

into the aorta and keep the blood from flowing back. If any one of these

valves becomes diseased it may not thoroughly close the opening it is

placed to guard and then we have a train of important symptoms.