Plasma is the liquid part of blood and is approxi-mately 91% water. The solvent ability of water enables the plasma to transport many types of sub-stances. Nutrients absorbed in the digestive tract, such as glucose, amino acids, and minerals, are circulated to all body tissues. Waste products of the tissues, such as urea and creatinine, circulate through the kidneys and are excreted in urine. Hormones produced by endocrine glands are carried in the plasma to their tar-get organs, and antibodies are also transported in plasma. Most of the carbon dioxide produced by cells is carried in the plasma in the form of bicarbonate ions (HCO3–). When the blood reaches the lungs, the CO2 is re-formed, diffuses into the alveoli, and is exhaled.
Also in the plasma are the plasma proteins. The clotting factors prothrombin, fibrinogen, and others are synthesized by the liver and circulate until acti-vated to form a clot in a ruptured or damaged blood vessel. Albumin is the most abundant plasma protein. It too is synthesized by the liver. Albumin contributes to the colloid osmotic pressure of blood, which pulls tissue fluid into capillaries. This is important to main-tain normal blood volume and blood pressure. Other plasma proteins are called globulins. Alpha and beta globulins are synthesized by the liver and act as carri-ers for molecules such as fats. The gamma globulins are antibodies produced by lymphocytes. Antibodies initiate the destruction of pathogens and provide us with immunity.
Plasma also carries body heat. Heat is one of the by-products of cell respiration (the production of ATP in cells). Blood is warmed by flowing through active organs such as the liver and muscles. This heat is dis-tributed to cooler parts of the body as blood continues to circulate
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