Blood circulates throughout the body in the cardiovascular system, which consists of the heart and the blood vessels. This principles forms a continuous circuit that delivers oxygen and nutrients to all cells and carries away waste product.
The Heart
The heart is placed between the lungs, with its point or apex directed toward the left. The thick muscle layer of the heart wall is the myocardium, which is lined on the inside with a thin endocardium and covered on the face with a thin epicardium. The heart is contained within a fibrous sac, the pericardium.
Each of the upper receiving chambers of the heart is an atrium. Each of the lower pumping chambers is a ventricle. The wall separating the two ventricles is the interventricular septum; the wall dividing the two atria is interatrial septum.
The right atrium receives blood low in oxygen from all body tissues straight through the classic vena cava and the inferior vena cava. The blood then enters the right ventricle and is pumped to the lungs straight through the pulmonary artery. Blood returns from the lungs high in oxygen and enters the left atrium straight through the pulmonary veins. From here it enters the left ventricle and is pumped into the aorta to be distributed to all tissues. Blood is kept involving in a forward direction by one-way valves-the bicuspid valve, regularly called mitral valve. And the tricuspid valve.
Each contraction of the heart, termed systole is followed by a leisure phase, diastole, while which chambers fill. Each time the heart beats, both atria ageement and immediately thereafter both ventricles contract.
The Vascular System
The vascular principles consists of arteries that carry blood away from the heart, arterioles-small arteries that lead into the capillaries, capillaries, the smallest vessels, straight through which exchanges take place between the blood and the tissues, veins, that carry blood back to the heart and venules - the small veins that receive blood from the capillaries and drain into the veins. Nervous principles stimulation can cause the diameter of a vessel to increase (vasodilation) or decrease (vasoconstriction).
The Lymphatic System
The fluid carried in the lymphatic principles is called lymph, and the role of the lymphatic principles in the circulation is to return excess fluid and the proteins from the tissues to the bloodstream. Other functions of the lymphatic principles contain absorption of digested fats from small intestines and protecting the body from invading microorganisms. Along the path of the lymphatic vessels are small masses of lymphoid tissue, the lymph nodes. Their function is to filter the lymph as it passes through. Other organs and tissues of the lymphatic principles contain the tonsils, the thymus and the spleen.
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