Anatomy & Physiology

Anatomy & Physiology Study Guide denser than water. Plasma is similar to interstitial fluid, although it contains a unique assortment of suspended proteins. A constant exchange of fluid between the tissues and the blood is driven by a combination of hydrostatic pressure, concentration gradients, and osmosis. Formed elements are blood cells and cell fragments that are suspended in plasma. Three types of formed elements exist: red blood cells, white blood cells, and platelets. Red blood cells (RBCs) or erythrocytes are the most abundant blood cells. These specialized cells are essential for the transportation of oxygen in the blood. The less numerous white blood cells (WBCs) , or leukocytes , participate in the body’s defense mechanisms. There are five classes of leukocytes, each with different functions. Platelets are tiny, membrane-bound pieces of cells that contain enzymes and other substances crucial to the process of clotting. Formed elements are created by the process of hemopoiesis . Two populations of stem cells—myeloid stem cells and lymphoid stem cells—are responsible for the production of all the kinds of formed elements. Together, the plasma and the formed elements constitute whole blood. The components of whole blood can be separated for analytical or clinical purposes. Blood temperature is roughly 38°C (100.4°F), slightly above normal body temperature. Blood is somewhat alkaline, with a pH between 7.35 and 7.45 (average: 7.4). The cardiovascular system of an adult male holds 5–6 liters (5.3–6.4 quarts) of whole blood, whereas that of an adult female contains 4–5 liters (4.2–5.3 quarts). Plasma Plasma makes up 46–63 percent of the volume of whole blood. Water accounts for 92 percent of the plasma volume. Together, plasma and interstitial fluid account for most of the volume of extracellular fluid (ECF) in the body. Plasma contains significant quantities of dissolved proteins. On average, plasma contains about five times the concentration of protein as interstitial fluid (7.6 g per 100 mL of plasma). The reason for this discrepancy is that proteins remain trapped in the circulatory system due to their large size and globular shapes. Three major types of plasma proteins exist: albumins, globulins, and fibrinogen. These three types compose more than 99 percent of the plasma proteins. The remainder consists of circulating enzymes, hormones, and prohormones. Approximately 60 percent of the plasma proteins are albumins . As the most abundant plasma proteins, they are major contributors to the osmotic pressure of plasma. Albumins transport fatty acids, thyroid hormones, some steroid hormones, and other substances. Globulins make up approximately 35 percent of all proteins in plasma. Antibodies and transport globulins are notable plasma globulins. Antibodies, also called immunoglobulins , attack foreign proteins and pathogens. The third major type of plasma protein, fibrinogen , functions in clotting. Fibrinogen normally accounts for roughly four percent of plasma proteins. Fibrinogen molecules interact and form large, insoluble strands of fibrin under conditions favorable for coagulation. Therefore, the basic framework for a blood clot involves these fibers. Steps must be taken to prevent clotting in a blood sample; otherwise, the conversion of fibrinogen to fibrin will occur. This conversion removes the clotting proteins, leaving a fluid known as serum . The clotting process also removes calcium ions and other

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