UKPCS Science Life Sciences-animal-bio: Blood- Components & Functions # 99

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Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells.Components of blood

Components of blood

Blood accounts for 7% of the human body weight. The average adult has a blood volume of roughly 5 litres  which is composed of plasma and several kinds of cells. By volume, the red blood cells constitute about 45% of whole blood, the plasma about 54.3%, and white cells about 0.7%.

These blood cells (which are also called corpuscles) consist of:

Erythrocytes: Red blood cells contain the blood’s hemoglobin and distribute oxygen. Mature red blood cells lack a nucleus and organelles in mammals. The red blood cells (together with endothelial vessel cells and other cells) are also marked by glycoproteins that define the different blood types.

Leukocytes: White blood cells are part of the body’s immune system; they destroy and remove old or aberrant cells and cellular debris, as well as attack infectious agents (pathogens) and foreign substances. The cancer of leukocytes is called leukemia.

Thrombocytes: Also called platelets, they take part in blood clotting (coagulation). Fibrin from the coagulation cascade creates a mesh over the platelet plug.


About 55% of blood is blood plasma, a fluid that is the blood’s liquid medium, which by itself is straw-yellow in color. The blood plasma volume totals of 2.7–3.0 liters (2.8–3.2 quarts) in an average human. It is essentially an aqueous solution containing 92% water, 8% blood plasma proteins, and trace amounts of other materials. Plasma circulates dissolved nutrients, such as glucose, amino acids, and fatty acids (dissolved in the blood or bound to plasma proteins), and removes waste products, such as carbon dioxide, urea, and lactic acid.

Other important components include:

  • Serum albumin
  • Blood-clotting factors (to facilitate coagulation)
  • Immunoglobulins (antibodies)
  • lipoprotein particles
  • Various other proteins
  • Various electrolytes (mainly sodium and chloride)

The term serum refers to plasma from which the clotting proteins have been removed. Most of the proteins remaining are albumin and immunoglobulins.

Functions of blood:

Blood performs many important functions within the body, including:

  • Supply of oxygen to tissues (bound to hemoglobin, which is carried in red cells)
  • Supply of nutrients such as glucose, amino acids, and fatty acids (dissolved in the blood or bound to plasma proteins (e.g., blood lipids))
  • Removal of waste such as carbon dioxide, urea, and lactic acid
  • Immunological functions, including circulation of white blood cells, and detection of foreign material by antibodies
  • Coagulation,
  • Regulation of core body temperature
  • Hydraulic functions

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