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Aortic Valve

When the left ventricle of the heart contracts, the bicuspid valve closes, and the only way out is through a large artery called the "aorta." The branches of the aorta distribute blood to all parts of the body (See Arch of the Aorta). At the base of the aorta, there is an "aortic semilunar valve" that has three leaflets or cusps. It opens to allow blood to leave the left ventricle as it contracts. When the ventricular muscles relax, the valve closes to prevent blood from backing up into the ventricular chamber.

Arch of The Aorta

The aorta is the largest artery in the body. It extends upward from the left ventricle of the heart, arches over the heart to the left, and descends just in front of the spinal column. The first portion of the aorta is the "ascending aorta," which branches into the "arch of the aorta." Three major arteries originate from the aortic arch: the "brachiocephalic artery," which supplies blood to the brain and head; the left common carotid artery and the left subclavian artery.

Chordae Tendinae

Strong, fibrous strings, called "chordae tendinae," are attached to the leaflets (or cusps) of the heart on the ventricular side; i.e., the lower chamber. These strings originated from small mounds of muscle tissue, the "papillary muscles," which project inward from the walls of the ventricle. When the cusps close, the chordae tendinae prevent them from swinging back into the atrium cavity (the upper chamber).

Descending Aorta

Although the descending aorta is positioned to the left of the body's midline, it gradually descends to directly in front of the vertebral column at the left of the 12th thoracic vertebra. The portion of the descending aorta above the diaphragm is called the "thoracic aorta" and gives off branches into the thoracic wall. These branches, the bronchial, pericardal, and esophageal arteries, supply blood to the organs for which they were named. Below the diaphragm, the descending aorta becomes the "abdominal aorta," stemming off into branches which reach the abdominal wall and various tissues and organs of the abdomen.

Inferior Vena Cava

The inferior vena cava is a large vein ascending through the abdomen. It collects blood from the hepatic veins, the lumbar veins, gonadal veins, renal veins, and phrenic veins. These vessels usually drain regions that are supplied by arteries with corresponding names. The inferior vena cava enters the heart through the right atrium.

Interventricular Septum

The left ventricle is separated from the right ventricle by the interventricular septum. It is slanted backwards and to the right, and it also curves to the right, which completes the oval of the thick ventricle and encroaches upon the chamber of the right ventricle. The greater part of it is thick and muscular. The upper portion, which separates the aortic vestible from the lower part of the right atrium and the upper part of the right ventricle, is much thinner and is fibrous.

Left Atrium

Internally, the heart is divided into four hollow chambers, two on the left and two on the right. The upper chambers, called "atria," have relatively thin walls and receive blood returning through the veins. The left atrium chamber of the heart receives blood from the lungs through four "pulmonary veins" - two from the right lung and two from the left lung. Blood passes from the left atrium into the left ventricle through the atrioventricular opening, which is guarded by a valve. This valve has two leaflets or cusps, and is called the "bicuspid valve." It prevents blood from flowing back into the left atrium from the ventricle and is attached to papillary muscles by the "chordae tendinae."

Ventricles

Internally, the heart is divided into four hollow chambers, two on the left and two on the right. The lower chambers, the "ventricles," force blood out of the heart into the arteries to be carried back to the various sites throughout the body. The right ventricle has a much thinner wall than the left ventricle. This chamber pumps blood a fairly short distance to the lungs. The left ventricle, however, must force blood to all other parts of the body against a great flow of resistance, so the walls are stronger.

Mitral Valve

The valve between the left atruim and left ventricle is called the bicuspid, or mitral valve, having two cusps forming the valve. Its cusps are attached to papillary muscles by way of the chordae tendinae and it allows blood to enter the left ventricle from the left atrium.

Pulmonary Artery/Vein

When the muscular wall of the right ventricle contacts, the blood inside the heart chamber is put under more pressure, and the tricuspid valve closes. As a result, the only exit is through the "pulmonary trunk," which divides to form the right and left "pulmonary arteries." At the base of this trunk is a "pulmonary semilunar valve" that is made up of three leaflets or cusps. This valve opens when the right ventricle contracts. When the right ventricular muscles relax, blood starts back up the pulmonary trunk, causing the valve to close to prevent the flow from returning into the ventricular chamber. The pulmonary vein travels parallel to the pulmonary artery as it carries the blood back up to the heart.

Right Atrium

Internally, the heart is divided into four hollow chambers, two on the left and two on the right. The upper chambers, called "atria," have relatively thin walls and receive blood returning through the veins. The right atrium receives blood from two large veins: the "superior vena cava" and the "inferior vena cava." These veins return blood that is low in oxygen from various sites in the body. A smaller vein, called the "coronary sinus," also drains blood into the right atrium from the wall of the heart.

Veins

Internally, the heart is divided into four hollow chambers, two on the left and two on the right. The upper chambers, called "atria," have relatively thin walls and receive blood returning through the veins. The lower chamber, the "ventricles," force blood out of the heart into the arteries to be carried back to the various sites throughout the body. Veins are responsible for returning blood to the heart after exchanges of gases, nutrients, and wastes have been made between the blood and the body cells. Veins begin when capillaries merge into venules, the venules into small veins, and the small veins merge into larger ones. They are harder to follow than the arteries, because these vessels are interconnected with irregular networks, so that many small unnamed venules may join to form a larger vein. On the other hand, larger veins typically parallel the courses taken by named arteries, and the veins are often given the same name as the companion arteries. The veins from all parts of the body (except from the lungs back to the heart) converge into two major paths that lead to the right atrium of the heart. These veins are the "superior vena cava" and the "inferior vena cava."

Tricuspid Valve

The "atrioventricular" opening between the right atrium and the right ventricle is guarded by a large "tricuspid valve," which is composed of three leaflets or "cusps." This valve permits blood to move from the right atrium into the right ventricle and prevents it from moving back the other way. The cusps fold out of the way when the blood pressure is greater on the atrium side, and they close when the pressure is greater on the ventricular side.