The Blood

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Blood

Blood (/blʌd/), from Old English blōd, 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.

Etymology

The word "blood" comes from the Old English blōd, which is derived from Proto-Germanic *blōþą.

Composition

In vertebrates, it is composed of blood cells suspended in blood plasma. Plasma, which constitutes 55% of blood fluid, is mostly water (92% by volume), and contains proteins, glucose, mineral ions, hormones, carbon dioxide (plasma being the main medium for excretory product transportation), and blood cells themselves.

Blood cells

There are two types of blood cells: red blood cells (RBCs or erythrocytes) and white blood cells (WBCs or leukocytes). Red blood cells contain a protein called hemoglobin that carries oxygen from the lungs to all parts of the body. White blood cells are part of the immune system and function in defending the body against both infectious disease and foreign materials.

Blood types

Human blood is grouped into four types: A, B, AB, and O. Each letter refers to a kind of antigen, or protein, on the surface of red blood cells. The Rh factor is another type of antigen on the surface of red blood cells. People who have the Rh factor are Rh positive (Rh+), while those who do not are Rh negative (Rh-).

Functions

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
  • 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

See also

External links

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