Human Circulatory System

Circulatory System


Did You Know That...? If a person's red blood cells were placed on top of one another, they would reach one-eighth of the distance to the moon.

Clotting of Blood

There are 3 main reactions that occur in the clotting of blood.

  1. When platelets are exposed to a rough surface such as that of damaged tissue, they disintegrate to produce a substance called thromboplastin.
  2. Thromboplastin acts like an enzyme to convert prothrombin (a plasma protein) to thrombin. (Normal blood contains an anti-coagulant called heparin that prevents the conversion of prothrombin to thrombin.)
  3. Thrombin then acts like an enzyme to convert fibrinogen (a soluble plasma protein) to fibrin that is insoluble. The fibrin fibres trap red and white blood cells to form a solid clot within minutes. Serum is the yellowish liquid that oozes from the shrinking clot.

Blood Vessels

Did You Know That...?

Structure of the Heart

Blood Flow through the Heart

Heart Beat

Blood Pressure

Double Circulation of Blood

There are 2 main circuits of blood flow in the body:

  1. Pulmonary Circuit - Deoxygenated blood from the heart goes to the lungs via pulmonary arteries. Oxygenated blood from the lungs goes back to the heart via the pulmonary veins.
  2. Systemic Circuit - The aorta (the main artery from the heart) leaves the left ventricle, and branches to take blood to the head (carotid artery), arms and chest. Other branches from the aorta supply the liver, intestines, kidneys and legs. The Vena Cava (the main veins to the heart) return deoxygenated blood from the body.

Did You Know That...? Cardiovascular diseases affecting the heart and blood vessels are the biggest cause of death worldwide. They may be prevented by healthy diet and exercise.

Comparison of Circulatory Systems in Animals

Other Gas-Carrying Pigments