Blood
Blood is a specialized bodily fluid (technically a tissue) that is composed of a liquid
called blood plasma and blood cells suspended within the plasma. The blood cells present in
blood are red blood cells (also called RBCs or erythrocytes), white blood cells (including both
leukocytes and lymphocytes) and platelets (also called thrombocytes). Plasma is
predominantly water containing dissolved proteins, salts and many other substances; and
makes up about 55% of blood by volume. Mammals have red blood, which is bright red when
oxygenated, due to hemoglobin. Some animals, such as the horseshoe crab use hemocyanin to
carry oxygen, instead of hemoglobin.
By far the most abundant cells in blood are red blood cells. These contain hemoglobin, an
iron-containing protein, which facilitates transportation of oxygen by reversibly binding to
this respiratory gas and greatly increasing its solubility in blood. In contrast, carbon dioxide is
almost entirely transported extracellularly dissolved in plasma. White blood cells help to resist
infections and parasites, and platelets are important in the clotting of blood.
Blood is circulated around the body through blood vessels by the pumping action of the heart.
Arterial blood carries oxygen from inhaled air to the tissues of the body, and venous blood
carries carbon dioxide, a waste product of metabolism produced by cells, from the tissues to
the lungs to be exhaled.
Blood performs many important functions within the body including:
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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)
Removal of waste such as carbon dioxide, urea and lactic acid
Immunological functions, including circulation of white cells, and detection of foreign
material by antibodies
Coagulation, which is one part of the body's self-repair mechanism
Messenger functions, including the transport of hormones and the signalling of tissue
damage
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Regulation of body pH (the normal pH of blood is in the range of 7.35 - 7.45)
Regulation of core body temperature
Hydraulic functions
Red blood cells are the most common type of blood cell and the vertebrate body's principal
means of delivering oxygen from the lungs or gills to body tissues via the blood.
Human red blood cells
Red blood cells are also known as RBCs, haematids or erythrocytes (from Greek erythros
for "red" and kytos for "hollow", with cyte nowadays translated as "cell").
A schistocyte is a red blood cell undergoing fragmentation, or a fragmented part of a red
blood cell.
White blood cells, or leukocytes, are cells of the immune system defending the body against
both infectious disease and foreign materials. Several different and diverse types of
leukocytes exist, but they are all produced and derived from a multipotent cell in the bon
marrow known as a hematopoietic stem cell. Leukocytes are found throughout the body,
including the blood and lymphatic system.
Blood types:
0 contains IgM anti-A antibodies and anti-B antibodies against the A and B blood group
antigens.
A individuals have the A antigen on the surface of their RBCs, and blood serum containing
IgM antibodies against the B antigen.
B individuals have the B antigen on the surface of their RBCs, and blood serum containing
IgM antibodies against the A antigen.
AB individuals have both A and B antigens on the surface of their RBCs, and their blood
serum does not contain any antibodies against either A or B antigen.