Systemic Circulation

Systemic Circulation is the system of blood vessels and associated tissues that supplies blood, and hence oxygen, to all parts of the body.

One way to describe systemic circulation is in the form of a diagram:

Diagram summarizing Systemic Circulation

This diagram and systemic circulation itself may be summarised in words as follows:

Oxygenated Blood

  • Oxygenated blood leaves the lungs and enters the Left Atrium (LA) of the heart via the pulmonary veins.
  • This oxygenated blood is then pumped from the Left Atrium (LA) of the heart to the Left Ventricle (LV) of the heart, and then out of the heart to the body tissues via the aorta, which is the major artery leaving the heart.
  • The aorta divides into other arteries that serve different parts of the body (as mentioned on the page about the
    structure of the heart
    ). These can be separated into two categories: blood supply to the upper-body, and blood supply to the lower-body.
  • Blood Supply to the Upper-Body:
    The aorta leads to the subclavian arteries that take blood to the arms (some of which eventually reaches the hands), and also to the carotid artery that carries blood to the head.
  • Blood Supply to the Lower-Body:
    The aorta also leads to the hepatic artery that carries blood to the liver,
    the mesenteric artery that carries blood to the small intestines,
    the renal arteries that carry blood to the kidneys,
    and the iliac arteries that carry blood to the legs (some of which eventually reaches the feet).

Deoxygenated Blood

  • Blood is deoxygenated when it leaves the tissues and organs it has supplied with oxygen and other nutrients, to return back to the pulmonary circulatory system.
    This can also be summarised for the upper-body and lower-body separately:
  • Return of Blood from the Upper-Body:
    Blood returns from the head via the jugular veins, and from the arms via the subclavian veins. All of the blood in the major veins of the upper body flows into the superior vena cava, which returns the blood to the right ventricle of the heart.
  • Return of Blood from the Lower-Body:
    Blood returns from the small intestines by passing through the hepatic portal vein to the liver.
    Blood returns from the liver via the hepatic vein, from the kidneys via the renal veins, and from the legs via the iliac veins. All of the blood in the major veins of the lower body flows into the inferior vena cava, which returns the blood to the right ventricle of the heart.
  • After re-entering the (right atrium of the) heart via the superior vena cava and the inferior vena cava, deoxygenated blood is pumped into the right ventricle of the heart and then out of the heart to the lungs via the pulmonary artery.
  • Deoxygenated blood enters the lungs and is oxygenated before leaving the lungs (as oxygenated blood), and so the cycle begins again ...

More about the structure and functions of the heart and vascular system are included on other pages of this website.


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