Sharon (The Heart)

 Sharon Bido #3  3A Nursering

The heart pumps the liquid clock that keeps us alive: blood. It is estimated that the heart beats at an average of 70 times per minute at rest. Pear-shaped, measures 12.5 inches long and weighs about 450 grams.

This powerful organ is located inside of the chest, between the lungs. It consists of a hollow muscle called myocardium, which in turn is coated on the inner and outer side of the endocardium, and pericardium, respectively.

It has four chambers: two upper chambers called atria, and two lower chambers, the ventricles. These cavities are separated by three types of partitions: the ASD, which divide the atria; the interventricular that divides the ventricles, and AV, which separates the atria from the ventricles.

Now that we know how our heart is formed, you've probably wondered how their cavities communicate if there are apparently partitions that separate them. Well, I'll explain: the right atrium communicates with the right ventricle through a hole called the atrioventricular right. At the edges of this hole is situated tricuspid valve.

The left atrium does the same with the left ventricle through the left atrioventricular orifice, whose contours the mitral or bicuspid valve is located.

These valves are extremely important, because let in blood from the atria to the ventricles but prevent passage in the opposite direction.

Two other valves, termed pulmonary and aortic, prevent the blood that is in the arteries flowing back into the ventricles.
pericardium

The heart is completely surrounded by a layer called pericardium. It is a pouch or carrying bag, which reduces friction between the heart and surrounding organs in the thoracic cavity.

The pericardium is supported by ligaments which act as supports of the heart, preventing it from moving too much with changes in body position. Furthermore, this layer is a barrier against the spread of infection.

It is composed of two membranes, called serous pericardium and epicardium or fibrous or parietal pericardium.

Between the two there is a space called the pericardial cavity, filled with pericardial fluid, which lubricates the surfaces and allows the heart to beat.

Function of the different layers of the heart

Fibrous or parietal pericardium is a sac formed by collagen fibers together with a network of elastic fibers.

Then the pericardium, three inner layers:

Serous pericardium or epicardium: the visceral layer surrounding the surface of the heart. Coronary arteries passing through this layer, penetrating the myocardium and endocardium.

Infarction: is the middle layer and the thickest of the heart wall. It is the only heart muscle, and contains nerve fibers that help pump blood through automatic contraction.

Endocardium is the innermost layer; is formed by a flat membrane, and allows blood to flow easily through all four chambers of the heart (atria and ventricles). The endocardium has three layers: internal or endothelial or subendothelial and external media or subendocardial.

Cycle and cardiac conduction

Heartbeat is a movement of contraction and relaxation (or dilation). At first it is called systole and the second is known as diastole. The pulse is called a full cardiac cycle occurs in three stages:

Atrial systole: the atria contract to propel the blood into the ventricles were empty. The mitral and tricuspid valves open to allow the passage of blood.

Ventricular systole: following closure of the two valves that had been previously opened, the first heartbeat occurs. Next, the aortic and pulmonary valves open by the great flow of blood entering the ventricles.

Diastole: passing blood, aortic and pulmonary valve is closed, the heart muscle relaxes, the blood enters the atria and its back pressure causes the mitral and tricuspid valves open. Then the cycle repeats.

Other layers of the heart

Among the cardiac layers above named are two sliding and damping:

- Subendocardial layer: consists of loose connective tissue (relaxed) which is attached to the perimysium (connective tissue) of the myocardium. It contains blood and lymph vessels, nerve fibers and some ganglion cells.

- Layer subepicardial: has abundant adipose tissue, which contains loose connective tissue, coronary vessels, nerves and ganglia.

pericarditis

It is a disease caused by inflammation of the pericardium. You can develop for two reasons mainly, viral or idiopathic (unknown), the latter being the most common. When it is caused by a virus, it can be preceded by a cold, sore throat or any other viral disease.