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FUNCTIONS OF BLOOD
Blood has always fascinated humans, and throughout history they have speculated about its function. Some societies consider blood the “essence of life” because the uncontrolled loss of it can result in death. Many cultures around the world, both ancient and modern, believe blood has magical qualities. Blood has also been thought to define our character and emotions. For example, people of a noble bloodline are sometimes described as “blue bloods,” whereas criminals are said to have “bad” blood. People commonly say that anger causes their blood to “boil,” whereas fear makes it “curdle.” The scientific study of blood reveals characteristics as fascinating as any of these fantasies. Blood performs many functions essential to life and can reveal much about our health. The heart pumps blood through blood vessels that extend throughout the body. Blood helps maintain homeostasis in several ways:
1. Transport of gases, nutrients, and waste products. Oxygenenters the blood in the lungs and is carried to cells. Carbon dioxide, produced by cells, is carried in the blood to the lungs, from which it is expelled. The blood transports ingested nutrients, ions, and water from the digestive tract to cells, and the blood transports the waste products of the cells to the kidneys for elimination.
2. Transport of processed molecules. Many substances areproduced in one part of the body and transported in the blood to another part, where they are modified. For example, the precursor to vitamin D is produced in the skin and transported by the blood to the liver and then to the kidneys for processing into active vitamin D. Then the blood transports active vitamin D to the small intestine, where it promotes the uptake of calcium. Another example is lactate produced by skeletal muscles during anaerobic respiration . The blood carries lactate to the liver, where it is converted into glucose.
3. Transport of regulatory molecules. The blood carries manyof the hormones and enzymes that regulate body processes from one part of the body to another.
4. Regulation of pH and osmosis. Buffers , whichhelp keep the blood’s pH within its normal limits of 7.35–7.45, are found in the blood. The osmotic composition of blood is also critical for maintaining normal fluid and ion balance.
5. Maintenance of body temperature. Warm blood istransported from the interior of the body to the surface, where heat is released from the blood. This is one of the mechanisms that helps regulate body temperature.
6. Protection against foreign substances. Certain cells andchemicals in the blood constitute an important part of the immune system, protecting against foreign substances, such as microorganisms and toxins.
7. Clot formation. When blood vessels are damaged, bloodclotting protects against excessive blood loss. When tissues are damaged, the blood clot that forms is also the first step in tissue repair and the restoration of normal function.
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