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Heart structure

Parts of our heart

Heart is covered by a double-layered heart membrane called pericardium. On the outer surface of pericardium, the borders of the heart chambers and the coronary network are visible, which are responsible for the nourishment of the heart. The primary funcion of pericardium is to protect the heart and fix it to the breastbone, spine and other parts of chest cavity by the means of ligaments.

In the inner side of pericardium we can find the heart wall, which consists of 3 histological layers. The outer one is the single-layer endothel. Under that there is the myocardium (you can learn more here), which is built up of special muscle tissues, called cardiac muscle. The inner, third part is the endocardium, which is a membrane of connective tissue.

The interior of the heart has left and right side separated by a thick, muscular wall called septum. Each side has an upper chamber called atrium and a lower chamber called ventricle, divided by valves. Atrias are smaller than the ventricles, and their walls are thinner. Their job is to hold the blood before it goes down to the ventricles. The ventricles are bigger and have thicker muscular walls (3 layers of muscle). Their job is to pump the blood. The right ventricle pumps blood to the lungs, while the left ventricle pumps blood to all other parts of the body. For this reason, the left ventricle has a thicker muscular wall. For the best, continuous circulation, the heart muscles are wrapped around ringwise. 

The Atrium Dextrum is an oval hollow, its inside wall is partly smooth (sinus venosus), partly reticulated (Atrium Primitivum). Blood low in oxygen from the systemic circulation enters the right Atrium from the Superior and Inferior Vena Cavae and passes to the Right Ventricle. The Superior Vena carries blood from the upper parts of the body (head, neck, upper limbs), while the Inferior Vena Cava carries blood from all other parts of the body. On the border of the Right Atrium and Right Ventricle (Ventriculus Dexter) is the Ostium Venosum Dextrum, which binds the 2 parts together. The Sinus Coronarius – which collects the blood of the heart- enters into the Right Atrium between the Ostium Venosum Dextrum and the inflow of Vena Cava Superior. The Right Atrium is situated on the breast, fitted together with the breastbone and ribs. Its cross-sectional picture is a half-moon, and sorrounds the Left Atrium. It has a thickness of 5 mm. Between the Ostium Venosum Dextrum and Right Atrium is the Valvula Tricuspidalis, which ensures that the blood flows into one direction.

Valves join to the Musculi Papillares by means of Chordae Tandineae. There are the three half-moon-shaped Valvula-semilunaris by the hole of Arteria Pulmonaris, which is coming from the Ostium Arteria Dextrum of Right Ventricle. The perfect insertion of Valvula Semilunaris assists the one-way flow of blood.

The structure of Oval Atrium Sinistrum is similar to the Atrium Dextrum.  This is situated on the back side of the heart. The blood rich in oxygen enters the Left Atrium from 2-2 Vena Pulmonalises. The left side of the heart is divided into two parts by the Ostium Venosum Sinistrum. The blood gets through this from the left Atrium to the Left Ventricle. Valvula bicuspidalis is situated on the verge of the Left Atrium and Ostium Venosum Sinistrum. Left Atrium has a very similar structure to the Right Atrium, but its wall is much thicker (approximately 10 mm). The main Artery of our body comes from the Ostium Arteria Sinistrum which is closed by 3 half-moon-shaped valves. The Arteria Coronaria derive from the wall of Aorta and Valves, these are called Right and Left Sinus Valsavae. These Coronary Arteries provide heart with blood. Heart attack happens when Coronary Arteries are blocked. The Fossa Ovalis is a nook situated along the Septum, between the Right Ventricle and Left Ventricle, which is remanence from the fetal circulation. 

The functioning of heart

Blood from the lungs and the body arrives to the left and right Atriums and flows towards the Ventricles, then they pump the blood to the lungs and to the whole body again. The right side of the heart is responsible for pumping deoxigenated blood (blue) coming from the body, while the left side of heart pumps the oxigenated blood (red) coming from lungs.

The oxigenated blood and deoxigenated blood cannot get mixed, because there is the Septum (separating wall) between the Atriums and Ventricles. The Septum prevents the two different kinds of blood to get mixed. 

The process of blood circulation:

Deoxigenated blood arrives to the Right Atrium from the body through two big veins. Blood goes to the Right Ventricle through the Tricuspid Valve, and the heart pumps the blood to the lungs from here. Deoxigenated blood arrives to the lungs, where it gets oxygen and goes back to the Left Atrium through the left and right Pulmonary Arteries. From here, blood gets to the Left Ventricle through the Mitral Valve, which pumps the oxigenated blood through the Aorta back to the body.

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Széchenyi 2020