The human heart is a four-chambered muscular organ, shaped and also sized roughly like a man"s closeup of the door fist with two-thirds the the mass come the left the midline.

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The love is enclosed in a pericardial sac that is lined through the parietal layers of a serous membrane. The visceral layer of the serous membrane forms the epicardium.

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Layers of the love Wall

Three class of tissue form the love wall. The external layer the the heart wall surface is the epicardium, the middle layer is the myocardium, and the inner great is the endocardium.

Chambers the the Heart

The interior cavity the the love is separated into 4 chambers:

Right atriumRight ventricleLeft atriumLeft ventricle

The two atria space thin-walled chambers that receive blood from the veins. The two ventricles room thick-walled chambers that forcefully pump blood the end of the heart. Differences in thickness that the heart chamber wall surfaces are as result of variations in the quantity of myocardium present, which mirrors the lot of force each room is forced to generate.

The best atrium obtain deoxygenated blood from systemic veins; the left atrium obtain oxygenated blood indigenous the pulmonary veins.

Valves the the Heart

Pumps require a set of valves to store the fluid flowing in one direction and the heart is no exception. The heart has actually two species of valves that keep the blood flow in the correct direction. The valves between the atria and ventricles are dubbed atrioventricular valves (also dubbed cuspid valves), if those in ~ the bases of the large vessels leave the ventricles are dubbed semilunar valves.

The ideal atrioventricular valve is the tricuspid valve. The left atrioventricular valve is the bicuspid, or mitral, valve. The valve in between the right ventricle and pulmonary stems is the pulmonary semilunar valve. The valve in between the left ventricle and also the aorta is the aortic semilunar valve.

When the ventricles contract, atrioventricular valves close to stop blood native flowing ago into the atria. When the ventricles relax, semilunar valves close to stop blood from flowing earlier into the ventricles.

Pathway of Blood v the Heart

While the is practically to describe the circulation of blood with the best side of the heart and also then through the left side, it is vital to realize the both atria and also ventricles contract in ~ the exact same time. The heart works as two pumps, one top top the right and one top top the left, working simultaneously. Blood flows from the right atrium to the right ventricle, and then is pumped come the lung to get oxygen. Native the lungs, the blood flows to the left atrium, then to the left ventricle. From there it is pumped come the systemic circulation.

Blood supply to the Myocardium

The myocardium that the heart wall is a working muscle that needs a constant supply of oxygen and also nutrients to function efficiently. For this reason, cardiac muscle has substantial network that blood vessels to bring oxygen come the contracting cells and to remove waste products.

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The right and also left coronary arteries, branches of the ascending aorta, supply blood come the wall surfaces of the myocardium. ~ blood passes with the capillaries in the myocardium, the enters a device of cardiac (coronary) veins. Most of the cardiac veins drainpipe into the coronary sinus, i m sorry opens right into the right atrium.