Blood is specialized body fluid in the circulatory system of humans that delivers necessary substances such as nutrients and oxygen to the cells.
The Blood cells are mainly
- Red Blood Cells (also called RBC or Erythrocytes)
- White Blood Cells (also called WBC or Leukocytes)
- Platelets (also called Thrombocytes)
The most abundant cells in humans are red blood cells, these contain Hemoglobin, an Iron-containing protein, which facilitates oxygen transport by reversibly binding to this respiratory gas thereby increasing its solubility in 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, the response to a broken blood vessel, the conversion of blood from a liquid to a semisolid gel to stop bleeding
- Messenger functions, including the transport of hormones and the signaling of tissue damage
- Regulation of core body temperature
Blood accounts for 7% of the human body weight. The average adult has a blood volume of roughly 5 liters and by volume, the red blood cells constitute about 45% of whole blood, and the plasma about 54.3%, and white blood cells about 0.7%.
Human blood fractioned by centrifugation :
- Plasma (Upper, yellow layer)
- Buffy coat (middle, thin white layer)
- Erythrocyte (bottom, red layer)
