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Blood Vessels

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Blood Vessels Artery Arteries are very close to the heart and they receive blood that is directly and forcefully pumped out from the left ventricle of the heart. The walls of arteries have a thick elastic muscular layer, which allows the walls to stretch and recoil easily. This structural feature enables arteries to withstand (prevent the bursting / tearing of the walls) and sustain (to maintain the driving force for distribution of the blood around the body) the high blood pressure. Vein Veins are situated far away from the heart (the forceful pumping of the left ventricle), and thus the blood flowing through them is at low pressure. ...read more.


Note: Remember the skeletal muscular pump ... that would involve the contractions of skeletal muscles pressing aganist the walls of the valves to "squeeze" the blood up the vein towards the heart. Compare between cross-sections of artery and vein Can you differentiate the artery from the vein in the above diagram? Artery: - thicker wall (thicker elastic muscular layer) - smaller (rounded) lumen Vein: - thinner wall (thinner elastic muscular layer) - larger (irregularly-shaped) lumen Capillary Blood capillaries transport blood from the arterioles to the venules. The lumens of blood capillaries are very tiny (really microscopic!), allowing them to come into close contact with many tissue cells (shorter diffusion distance). ...read more.


Their bell-shape also allows a larger surface area for the exchange of substances by diffusion) Note: The branching network of blood capillaries (very large cross-sectional area) greatly reduces the velocity of blood flow through the blood capillaries, allowing more time for the exchange of substances between the tissue cells and blood. One question .... what directly surrounds the blood capillaries? Tissue fluid! Tissue fluid is water and other dissolved substances which are being forced out through the blood capillary walls due to high bllod pressure at the arteriole end of the blood capillary. Another question ... how is tissue fluid differ in composition from blood plasma ... same? Nope! Tissue fluid does not contain plasma proteins. how about tissue fluid and blood? Tissue fluid does not have any red blood cells (too big to squeeze through the tiny pores of the blood capillary walls) ...read more.

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