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
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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