The Human Heart Essays - Blood Pressure, Cardiovascular Physiology

The Human Heart Essays - Blood Pressure, Cardiovascular Physiology The Human Heart Biology - Histology The Human Heart. Abstract: Dorland's Illustrated Medical Dictionary defines the heart as "the viscus of cardiac muscle that maintains the circulation of the blood". It is divided into four cavities; two atria and two ventricles. The left atrium receives oxygenated blood from the lungs. From there the blood passes to the left ventricle, which forces it via the aorta, through the arteries to supply the tissues of the body. The right atrium receives the blood after it has passed through the tissues and has given up much of its oxygen. The blood then passes through the right ventricle into the lungs where it gets oxygenated. There are four major valves in the heart; the left atrioventricular valve (also known as the mitral or bicuspid valve), the right atrioventricular valve (tricuspid), aortic valve, and the pulmonary valve. The heart tissue itself is nourished by the blood in the coronary arteries.2 Position of the Heart Within the Body: The heart is placed obliquely in the chest. The two atria are directed upwards and backwards to the right and are at the level of the fifth through the eight dorsal vertebrae. The apex of the heart points downwards and forwards to the left and corresponds to the interspace between the fifth and sixth ribs, two inches below the left nipple. Its atrial border corresponds to a line drawn across the sternum on a level with the upper border of the third costal cartilage. Its lower border (apex) corresponds to a line drawn across the lower end of the same bone, near the xiphoid process. Its upper surface is rounded and convex, directed upwards and forwards, and formed mainly by the right ventricle and part of the left ventricle. The posterior surface of the heart is flattened and rests upon the diaphragm muscle. Of its two borders, the right is the longest and thinnest, the left is shorter but thicker and round. Size: In an adult, the heart measures about five inches in length, three and a half inches in the broadest part of its transverse diameter, and two and a half inches in its antero-posterior. The average weight in the male varies from ten to twelve ounces. In the female, the average weight is eight to ten ounces. The heart will continue to grow in size up to an advanced period of life. This growth is more obvious in men than in women.3 Circulation of Blood in an Adult: The heart is subdivided by a longitudinal muscular septum into two lateral halves which are named right and left according to their position. A transverse muscle divides each half into two cavities. The upper cavity on each side is called the atria/auricle, and the lower side is called the ventricle. The right atrium and ventricle form the venous side of the heart. Dark venous blood is pumped into the right atrium from the entire body by the superior (SVC) and inferior vena cava (SVC), and the coronary sinus. From the right atrium, the blood passes into the right ventricle and from the right ventricle, through the pulmonary artery into the lungs.3 Once the blood becomes oxygenated/arterialized by its passage through the lungs, it is returned to the left side of the heart by the pulmonary veins which open into the left atrium. From the left atrium, the blood passes into the left ventricle where it is distributed by the aorta and its subdivisions through the entire body. Morphology of Each Heart Chamber: The right atrium is a little longer than the left. Its walls are also somewhat thinner than the left. The right atrium is capable of containing about two ounces of fluid. It consists of two parts, a principle cavity/sinus, and an appendix auriculae. The sinus is a large quadrilateral-shaped cavity located between the IVC and the SVC. Its walls are extremely thin and are connected on the lower surface with the right ventricle and internally with the left atrium. The rest of the right atrium is free and unattached. The appendix auricle is a small conical muscular pouch. It projects from the sinus forwards and to the left side, where it overlaps the root of the pulmonary artery.6 There are four main openings into