THE HEART: ANATOMY, STRUCTURE, AND BLOOD SUPPLY

March 24, 2024July 11, 2022 by chitasmita.com

The heart is a roughly cone-shaped hollow muscular organ lying between the lungs, with the pointed end (apex) directed downward, forward, and to the left. The heart is about 10 cm long and is about the size of the owner’s closed fist. It weighs about 225g in women and is heavier in men ( about 310g ). Its wall consists large of cardiac muscle (myocardium), lined and surrounded by membranes ( endocardium, pericardium).

Contents hide

1 POSITION OF HEART

1.1 ORGANS ASSOCIATED WITH what-is-respiration?

1.1.1 HEART STRUCTURE

1.1.1.1 INTERIOR OF THE HEART

1.1.2 FLOW OF BLOOD THROUGH THE HEART

1.1.2.1 BLOOD SUPPLY TO THE HEART https://www.webmd.com/heart-disease/high-cholesterol-healthy-heart

1.2 Related

POSITION OF HEART

It lies in the thoracic cavity in the mediastinum. It lies obliquely, a little more to the left than the right, and presents a base above and an apex below. The apex is about 9 cm to the left of the midline at the level of the 5th intercostal space, i.e. a little below the nipple and slightly nearer the midline. The base extends to the 2nd rib.

ORGANS ASSOCIATED WITH what-is-respiration?

INFERIORLY – The apex rests on the central tendon of the diaphragm.

SUPERIORLY – The great blood vessels, i.e. the aorta, superior vena cava, pulmonary artery, and pulmonary veins.

POSTERIORLY – The esophagus, trachea, left and right bronchus, descending aorta, inferior vena cava, and thoracic vertebrae.

LATERALLY – The lungs – the left lung overlaps the left side of the heart.

ANTERIORLY – The sternum, ribs, and intercostal muscles.

HEART STRUCTURE

It has three layers of tissue pericardium, myocardium, and endocardium.

PERICARDIUM

The pericardium is of two sacs. The outer sac consists of fibrous tissue and the inner of a continuous double layer of serous membrane.

The outer fibrous sac is continuous with the tunica adventitia of the great blood vessels above and adherent to the diaphragm below. Its inelastic, fibrous nature prevents overdistension of the heart.

The outer layer of the serous membrane, the parietal pericardium, lines the fibrous sac. The inner layer, the visceral pericardium, or epicardium, is continuous with the parietal pericardium and is adherent to the heart muscle.

The serous membrane consists of flattened epithelial cells. It secretes serous fluid into the space between the visceral and parietal layers, which allows smooth movement between them when the heart beats. The space between the parietal and visceral pericardium is only a potential space. In health, the two layers are closely associated, with only the thin film of serous fluid between them.

MYOCARDIUM

The myocardium is composed of specialized cardiac muscle found only in the heart. It is not under voluntary control but, like skeletal muscle, cross-stripes are seen on microscopic examination. Each fiber (cell) has a nucleus and one or more branches. The cells’ ends and branches are in very close contact with the ends and branches of adjacent cells.

The myocardium is thickest at the apex and thins out towards the base. It reflects the amount of work each chamber contributes to pumping blood. It is thickest in the left ventricle, which has the most outstanding workload.

ENDOCARDIUM

That lines the chambers and valves of the heart. It is a thin, smooth, glistening membrane that permits a smooth flow of blood inside the heart.

INTERIOR OF THE HEART

It is divided into a right and left side by the septum, a partition consisting of the myocardium covered by the endocardium. After birth, do not cross the septum from one side to the other. Each side is divided by an atrioventricular valve into an upper chamber, the atrium, and a lower chamber, the ventricle. The atrioventricular valves are formed by double folds of endocardium strengthened by a little fibrous tissue. The right atrioventricular valve (tricuspid valve) valve has three flaps or cusps, and the left atrioventricular valve has two cusps. The flow of blood in the heart is one way; blood enters the heart via the atria and passes into the ventricles below.

The valves between the atria and ventricles open and close passively according to changes in pressure in the chambers. They open when the pressure in the atria is greater than in the ventricles. During ventricular systole (contraction), the pressure in the ventricles rises above that in the atria, and the valves snap shut, preventing the backward flow of blood.

FLOW OF BLOOD THROUGH THE HEART

The two large veins of the body, the superior and inferior vanae cavae, empty their contents into the right atrium. This blood passes via the atrioventricular valve into the right ventricle. It is pumped into the pulmonary artery or trunk-only artery in the body that carries deoxygenated blood. The opening of the pulmonary artery is guarded, by the pulmonary valve, formed by three semilunar cups. This valve prevents the backflow of blood into the right ventricle when the ventricular muscle relaxes. After leaving pulmonary artery divides into left and right pulmonary arteries, which carry the venous blood to exchange gases.

Two pulmonary veins from each lung carry oxygenated blood back to the left atrium. Blood then passes through the left atrioventricular valve into the left ventricle. From it is pumped into the aorta, the first artery of the general circulation. Formed by three semilunar cusps.

From this sequence of events, the blood passes from the right to the left side of the heart via the lungs or pulmonary circulation.

BLOOD SUPPLY TO THE HEART https://www.webmd.com/heart-disease/high-cholesterol-healthy-heart

FIRSTLY ARTERIAL SUPPLY- The heart is supplied with arterial blood by the right and left coronary arteries, which branch from the aorta immediately distal to the aortic valve. The coronary arteries receive about 5 percent of the blood pumping from the heart, although they comprise a small proportion of body weight. This blood supply, especially to the left ventricle, highlights the importance of the heart to body function. The coronary arteries traverse the heart.

SECONDLY, VENOUS DRAINAGE- Most venous blood in several small veins join to form the coronary sinus, which opens into the right atrium. The remainder passes directly into the heart chambers through venous channels.