It is described as a closed circulatory system in that blood is circulated round the body through a system of interconnecting blood vessels. The human circulatory system is also described as double circulation in that blood has to flow twice through the heart before one complete circulation can be made through each time it does. It flows through separate pathways.


The two pathways are known as the:

  1. Lung or Pulmonary pathway.
  2. Body or systemic pathway.

The lung pathway ensures re-oxygenation of the blood while the body pathway ensures delivery of oxygen to the tissues and cells of the body.


Blood Defects and Diseases

Some people may suffer through not having enough RBCs and hence are unable to get sufficient supply of oxygen. These people can be said to be Anaemic. Thus, anemia is a serious blood defect. Other blood diseases abound and are named below viz:

  1. Leukaemia
  2. Haemophilia
  3. Sickle cell
  4. Septicemia
  5. Hypertension
  6. Hypotension

Leukaemia: Imbalance of red and white blood cells as there is a preponderance of defective and cancerous WBCs. This is caused by exposure to radioactive fall-out from atomic bombs or by over exposure to x-rays.

Sickle Cell: This is a disease which arises from the formation of sickle shaped red blood cells in the blood and which are unable to deliver the oxygen requirement of the body promptly and effectively. It is hereditary.

Haemophilia: Inability of the blood to check blood loss automatically when minor injuries are sustained. It is also hereditary. 

Septicemia: Blood poisoning due to certain bacterial infections and which results in lacking of the blood 

Hypertension:        Describes the clinical condition of high blood pressure.

Hypotension:          Low blood pressure. Occasionally, bleeding may occur when blood vessels are damaged or ruptured in accidents, wounds and certain illnesses.


See also

Water and Chemical Pollution

Air and Noise Pollution

Environmental Health

Classes of food


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