Anatomy and Function of the Human Heart: A Comprehensive Guide, Assignments of Anatomy

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THE HEART

The heart is a muscular pump that serves

two functions:

1) to collect blood from the tissues of the

body and pump it to the lungs; and

2) to collect blood from the lungs and

pump it to all tissues of the body.

The human heart lies in the protective

thorax, posterior to the sternum and costal

cartilages, and rests on the superior surface

of the diaphragm.

Within the mediastinum, the heart is

separated from the other mediastinal

structures by a tough membrane known as

the pericardium, or pericardial sac, and sits

in its own space called the pericardial

Internal Anatomy

The internal anatomy of the heart reveals

four chambers composed of cardiac muscle

or myocardium.

The atria: These are the two upper chambers, which receive blood. The ventricles: These are the two lower chambers, which discharge blood.

The left and right atria are the upper, thin- walled chambers, which receive blood returning to the heart. The lower, thick-walled chambers are the ventricles, which pump blood into the arteries leaving the heart. A wall of tissue called the septum separates the left and right atria and the left and right ventricle. Valves separate the atria from the ventricles. Note the ventricular septum separating the left ventricle from the right ventricle, and the

The heart has two atrioventricular

valves and two semilunar valves. The

tricuspid atrioventricular valve has three

flaps, or cusps, and occur between the

right atrium and ventricle. The mitral or

bicuspid atrioventricular valve has only

two cusps; it separates the left atrium

and ventricle. The tricuspid and bicuspid

atrioventricular valves are indicated in

the superior sectional view.

The pulmonic semilunar valve and the aortic semilunar valve are located at the base of the pulmonary trunk and aorta respectively. They each have three cusps and prevent the backflow of blood from the arteries into the ventricles during ventricular diastole, the relaxation of the ventricles. The pulmonic semilunar valve is indicated in both the coronal section of the heart and the superior sectional view. The aortic semilunar valve is shown only in the superior sectional view.

Walls of the Heart The walls of the heart consists of three layers. The thick myocardium is composed of cardiac muscle tissue. It is covered by two thin serous membranes attached to the muscle tissue: an inner endocardium and an outer epicardium or visceral pericardium. External to the epicardium is the double-layered parietal pericardium, composed of an inner serous membrane and an outer fibrous membrane. The pericardial cavity lies between the epicardium and parietal pericardium. Fluid secreted by the serous membranes reduces friction, enabling the heart to move freely within the pericardial sac.

Vessels of the Heart

The major vessels of the heart are the

two venae cavae, four pulmonary veins, a

pulmonary trunk, and the aorta. During

diastole, blood is returned to the atria.

Deoxygenated blood is returned to the

right atrium from body regions above the

heart by the superior vena cava and from

body regions below the heart by the

Simultaneously, oxygenated blood is

returned to the left atrium by the left and

right pulmonary veins.

During systole, blood is pumped from

the ventricles. Deoxygenated blood is

carried from the right ventricle to the lungs

via the pulmonary trunk, which branches to

form the left and right pulmonary arteries.