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Cardiovascular SystemHuman cardiovascular system consist of following components:-

  • Heart
  • Blood Vessels
  • Blood
  • Lymphatic system

Human heart is a muscular organ, consists of 4 chambers, 2 atria and 2 ventricles. It is roughly a size of fist, weigh between 250-350 mg. The heart is surrounded by a layer called pericardium, beneath is muscular layer (myocardium) and innermost is endocardium.

The tricuspid valve separate right atria and right ventricle while bicuspid valve (mitral) separate left atria and left ventricle. The semilunar valves are present between big vessels and ventricles. The pump mechanism of heart is responsible for circulation of oxygenated blood in the whole body. There are two type of circulation, pulmonary and systemic.

In the pulmonary circulation, deoxygenated blood leaves the right ventricle of the heart via the pulmonary artery and travels to the lungs, then returns as oxygenated blood to the left atrium of the heart via the pulmonary vein. In the systemic circulation, oxygenated blood leaves the body via the left ventricle to the aorta, and from there enters the arteries and capillaries where it supplies the body's tissues with oxygen. Deoxygenated blood returns via veins to the venae cavae, re-entering the heart's right atrium. The pacemaker cells present in the right atrium generates impulse which initiates contraction of heart. The impulse travel via SA node to AV node, bundle of his, purkinje system and then to right ventricles. The travelling impulse may be recorded on paper strip as ECG. The contracting phase of heart is called systole while relaxation phase is called diastole.

The blood vessels consist of arteries, arterioles, capillaries, venules, and veins. All blood is carried in these vessels. The arteries, which are strong, flexible, and resilient, carry blood away from the heart and bear the highest blood pressures. Because arteries are elastic, they narrow (recoil) passively when the heart is relaxing between beats and thus help maintain blood pressure. Capillaries are tiny, extremely thin-walled vessels that act as a bridge between arteries (which carry blood away from the heart) and veins (which carry blood back to the heart). The thin walls of the capillaries allow oxygen and nutrients to pass from the blood into tissues and allow waste products to pass from tissues into the blood. Blood flows from the capillaries into very small veins called venules, then into the veins that lead back to the heart.

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