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Chapter: Anatomy and Physiology for Health Professionals: Blood

Plasma suspends the cells and platelets of the blood. It is a clear, straw-colored liquid made up of 90% water, with organic and inorganic biochemicals.


Plasma suspends the cells and platelets of the blood. It is a clear, straw-colored liquid made up of 90% water, with organic and inorganic biochemicals. In many respects the composition of plasma resembles intersti-tial fluid. It also contains amino acids, carbohydrates, lipids, proteins, hormones, electrolytes, vitamins, and waste materials. An average adult has approximately 5 liters or approximately 5.3 quarts of blood in his or her body. A person who has low blood volume is referred to as hypovolemic.

Concentrations of major plasma ions are sim-ilar to those of the interstitial fluid, differing greatly from the concentrations inside cells. This is because water, ions, and over 100 small solutes are continu-ously exchanged between plasma and interstitial fluid across the walls of capillaries. Normally, the capillar-ies deliver more liquid and solutes to tissues than they remove from them. Plasma helps to transport gases, hormones, nutrients, and vitamins and also regulate fluid and electrolyte balance as well as pH levels. Elec-trolytes such as sodium and chloride are the most prevalent of the solutes in the plasma.

Plasma proteins are heavier than electrolytesand are not typically used as energy sources, remain-ing in the blood and interstitial fluids. By weight alone, the plasma proteins are the most abundant of the plasma solutes, making up approximately 8% of plasma weight. The liver synthesizes and releases more than 90% of the plasma proteins, including all albumins, fibrinogen, and most globulins. The plasma also contains products of cell activity and wastes. The primary difference between plasma and the interstitial fluid involves the concentration of dissolved oxygen and proteins. The temperature of blood is higher than body temperature.

Albumins are the smallest of the plasma proteinsbut make up around 60% of these proteins by weight. They are made in the liver and play an important role in the plasma’s osmotic pressure, transporting smaller molecules such as hormones and ions. Plasma pro-teins are too large to move through capillary walls, so they create an osmotic pressure to hold water in the capillaries, which is known as colloid osmotic pressure. This helps regulate water movement between blood and tissues, to aid in controlling blood volume and blood pressure. Therefore, albumins act as important blood buffers.

Globulins, which include alpha, beta, and gammaglobulins, make up around 36% of the plasma pro-teins. The alpha and beta globulins are produced by the liver, and are mostly transport proteins that bind to fat-soluble vitamins, lipids, and metal ions. The gamma globulins are antibodies released by plasma cells during the immune response. Fibrinogen, which makes up around 4% of the plasma proteins, is import-ant for blood coagulation. Under certain conditionsfibrinogen molecules interact to form large, insoluble strands of fibrin. This substance provides the basic framework for a blood clot. Fibrinogen is made in the liver and is the largest, in size, of the plasma proteins. TABLE 17 -1 summarizes albumins, globulins, fibrino-gen, and other plasma components.

Oxygen and carbon dioxide are the most import-ant blood gases, with nitrogen also contained in the plasma. Plasma nutrients include amino acids, nucle-otides, lipids, and simple sugars absorbed from the digestive tract. Glucose is transported in the plasma from the small intestine to the liver. In the liver, glu-cose is stored as glycogen or converted to fat. The concentration of glucose in the blood is represented in milligrams per deciliter (mg/dL). When the blood concentration of glucose drops, the potentially dan-gerous situation called hypoglycemia occurs. When glucose is elevated, it is called hyperglycemia, which can lead to diabetes. Plasma carries amino acids to the liver to manufacture proteins or to be used for energy. Plasma lipids include triglycerides, choles-terol, and phospholipids. Lipids are not water soluble, but the plasma is mostly made of water. Hence, lip-ids join with proteins to form lipoproteins, which the plasma can carry.

Nonprotein nitrogenous substances havenitrogen atoms but are not proteins. In the plasma these include amino acids, urea, and uric acid. Blood plasma also contains many electrolytes, which include potassium, calcium, sodium, magnesium, chloride, phosphate, bicarbonate, and sulfate ions. The most abundant types are sodium and chloride ions. All plasma constituents are regulated so their blood con-centrations remain mostly stable.

1. What are the main functions of blood?

2. Which plasma protein plays a key role in blood coagulation?

3. What are the functions of globulins?

4. Define the terms albumins, fibrinogen, and fibrin.

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