The heart has four chambers: two upper thin-walled atria or auricles and two lower thick-walled ventricles. The right side of the heart is completely separated from the left side by a wall called the septum.
Two large veins, the superior (anterior) and inferior (posterior) venae cavae, bringing dark red, deoxygenated blood from the various parts of the body (except the lungs), open into the right auricle. The pulmonary veins bringing bright red oxygenated blood from the lungs open into the left auricle. The openings of the veins into the auricle are controlled by rings of muscles found in the vein. Their contraction closes the openings, while their relaxation opens them.
The right auricle opens into the right ventricle. This opening is guarded by the triscupid valve. This valve has three flaps which are attached by cord-like tendons (chordae tendinae) to the walls of the right ventricle. These cords only allow the flaps to open outwards into the ventricle. Hence, the valves only allow a unidirectional blood flow from the auricle into the ventricle. The opening of the left auricle into the ventricle is guarded by the biscupid or mitral valve. This valve is structurally and functionally similar to the tricuspid valve except that it has two flaps instead of three.
The right ventricle opens out into the pulmonary artery, which branches into two, one leading to the right lung and the other to the left lung. These carry deoxygenated blood to the lungs. The left ventricle opens into the large aorta which branches to distribute oxygenated blood to all parts of the body except the lungs. Semi-lunar valves in these arteries prevent backflow of blood from the arteries into the ventricles.
The wall of the left ventricle is at least three times thicker than that of the right ventricle. This because the contraction of the left ventricle must send the blood the blood round the much longer systemic circulation, while that of the right ventricle only needs to send blood round the shorter pulmonary circulation. Thus, blood entering the aorta is at a very high pressure (about 105 mmHg), while that entering the pulmonary artery is at a much lower pressure (about 16 mmHg).
Two large veins, the superior (anterior) and inferior (posterior) venae cavae, bringing dark red, deoxygenated blood from the various parts of the body (except the lungs), open into the right auricle. The pulmonary veins bringing bright red oxygenated blood from the lungs open into the left auricle. The openings of the veins into the auricle are controlled by rings of muscles found in the vein. Their contraction closes the openings, while their relaxation opens them.
The right auricle opens into the right ventricle. This opening is guarded by the triscupid valve. This valve has three flaps which are attached by cord-like tendons (chordae tendinae) to the walls of the right ventricle. These cords only allow the flaps to open outwards into the ventricle. Hence, the valves only allow a unidirectional blood flow from the auricle into the ventricle. The opening of the left auricle into the ventricle is guarded by the biscupid or mitral valve. This valve is structurally and functionally similar to the tricuspid valve except that it has two flaps instead of three.
The right ventricle opens out into the pulmonary artery, which branches into two, one leading to the right lung and the other to the left lung. These carry deoxygenated blood to the lungs. The left ventricle opens into the large aorta which branches to distribute oxygenated blood to all parts of the body except the lungs. Semi-lunar valves in these arteries prevent backflow of blood from the arteries into the ventricles.
The wall of the left ventricle is at least three times thicker than that of the right ventricle. This because the contraction of the left ventricle must send the blood the blood round the much longer systemic circulation, while that of the right ventricle only needs to send blood round the shorter pulmonary circulation. Thus, blood entering the aorta is at a very high pressure (about 105 mmHg), while that entering the pulmonary artery is at a much lower pressure (about 16 mmHg).
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