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Blood and its transportation in the human body are vital for human life, health, and well-being. It provides the cells of the body with oxygen, necessary nutrients, hormones, removes carbon dioxide from cells, and delivers waste to the liver and kidneys. Blood also plays a crucial function in regulating body temperature. It is circulated throughout the body via arteries, capillaries, veins that have different structures and functions within the blood circulatory system.
Arteries are vessels that carry the blood away from the heart. The wall of an artery consists of three layers: the inner tunica intima, the middle tunica media, and the outer tunica externa (National Cancer Institute, 2021). The middle and outer layers are similar in size, with the tunica media consisting of muscle cells to ensure smooth blood flow and tunica externa formed from elastic and collagenous fibers that allow an artery to merge with surrounding tissue (National Cancer Institute, 2021). Pulmonary arteries carry blood from the right heart ventricle to the lungs, where it is enriched with oxygen (National Cancer Institute, 2021). Meanwhile, systemic arteries carry oxygenated blood from the left ventricle to body tissues (National Cancer Institute, 2021). These are large elastic arteries that receive blood directly from the heart and branch out into smaller arteries, including microscopic arterioles that regulate the flow of blood into the tissue capillaries (National Cancer Institute, 2021). Thus, the primary function of arteries is to ensure the flow of oxygenated blood throughout the body.
Capillaries are the smallest of the blood vessels in the circulatory system. Their essential function is to ensure the exchange of nutrients and waste between the blood and tissue cells and connect arterioles to venules (National Cancer Institute, 2021). Capillaries consist of a single layer of flattened endothelial cells that facilitates their exchange function (Paxton, 2021). Meanwhile, veins receive deoxygenated blood from capillaries and carry it toward the heart. Blood enters the smallest veins (venules) that later connect into larger systemic veins that facilitate blood flow to the right heart atrium (National Cancer Institute, 2021). Within the pulmonary circuit, the pulmonary vein carries oxygenated blood to the left atrium. Similar to arteries, veins consist of three layers with fewer muscle and connective tissue cells. In summary, arteries, capillaries, and veins perform distinct functions within the circulatory system and are structured differently to ensure their functions are fulfilled.
References
National Cancer Institute. (2021). Classification & structure of blood vessels. SEER Training. Web.
Paxton, S. (2021). Circulatory system: The histology guide. The Histology Guide. Web.
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