Blood Groups

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Blood groups are created by molecules present on the surface of red blood cells (and often on other cells as well).

The ABO Blood Groups

The ABO blood groups were the first to be discovered (in 1900) and are the most important in assuring safe blood transfusions.

The table shows the four ABO phenotypes ("blood groups") present in the human population and the genotypes that give

The Transport of Heat

In addition to its role in the transport of materials, the circulatory system is responsible for the distribution of heat throughout the body. This is true both of

  • endotherms, animals — birds and mammals — that generate internally the heat needed to maintain their body temperature. Birds and mammals are "warm-blooded' or homeothermic, maintaining their body temperature within narrow limits, no matter what the ambient temperature.
  • mesotherms, animals that generate heat

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Blood Clotting

When blood vessels are cut or damaged, the loss of blood from the system must be stopped before shock and possible death occur. This is accomplished by solidification of the blood, a process called coagulation or clotting.

A blood clot consists of

  • a plug