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Blood, plasma and functions

Blood is a circulating tissue composed of fluid plasma and cells. It is composed of different kinds of cells (occasionally called corpuscles); these formed elements of the blood constitute about 45% of whole blood. The other 55% is blood plasma, a fluid that is the blood's liquid medium, appearing yellow in color. The normal pH of human arterial blood is approximately 7.40 (normal range is 7.35-7.45), a weak alkaline solution. Blood is about 7% of the human body weight, so the average adult has a blood volume of about 5 liters, of which 2.7-3 liters is plasma.

When the formed elements are removed from blood, a straw-colored liquid called plasma is left

Blood plasma

When the formed elements are removed from blood, a straw-colored liquid called plasma is left. Plasma is about 92% water and 8.5% solutes, most of which by weight (7%) are proteins. Some of the proteins in plasma are also found elsewhere in the body, but those confined to blood are called plasma proteins.

Components of blood plasma

WATER (92%): Carries formed elements and dissolved substances; absorbs heat Major proteins.
Albumin controls water movement across membranes; affects blood viscosity (thickness), pressure, and volume; transports substances such as drugs.

Globulin forms antibodies to fight bacteria and viruses.
Fibrinogen forms fibrin and, with platelets, coagulates blood
Nonprotein nitrogen. Products of metabolism: urea, uric add, creatine, creatinine, ammonium salts; toxic if not removed; carried in blood to organs of excretion
Products of digestion. Amino acids, glucose, fatty adds – all needed by cells for energy, repair, and reproduction
Regulatory substances. Enzymes for cellular chemical reactions; hormones to regulate growth and development
Electrolytes. Sodium (Na+), potassium (K+), calcium (Ca++), magnesium (Mg+), chloride (Cl–), phosphate (PO4–), sulfate (SO4–), bicarbonate (HCO3–), and inorganic salts

Functions of blood


Blood transport oxygen form the lungs to the cells of the body and carbon dioxide from the cells to the lungs. It also carries nutrients from the gastrointestinal tract to the cells, heat and waste products away from cells and hormones form endocrine glands to other body cells.


Blood regulates pH through buffers. It also adjusts body temperature through the heat-absorbing and coolant properties of its water content and its variable rate of flow through the skin, where excess heat can be lost to the environment. Blood osmotic pressure also influences the water content of cells, principally through dissolved ions and proteins.


The clotting mechanism protects against blood loss, and certain phagocytic white blood cells or specialized plasma proteins such as antibodies, interferon, and complement protect against foreign microbes and toxins.

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