Systemic circulation
Systemic circulation is the part of the cardiovascular system which carries oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

ated blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 away from the heart to the body
With regard to living things, a body is the physical body of an individual. "Body" often is used in connection with appearance, health issues and death...

, and returns deoxygenated blood back to the heart. This physiologic theory of circulation
Circulation may refer to:*Circulatory system, a biological organ system whose primary function is to move substances to and from cells*Circulation , the path integral of the fluid velocity around a closed curve...

 was first described by William Harvey
William Harvey
William Harvey was an English physician who was the first person to describe completely and in detail the systemic circulation and properties of blood being pumped to the body by the heart...

. This term is opposed and contrasted to the term pulmonary circulation
Pulmonary circulation
Pulmonary circulation is the half portion of the cardiovascular system which carries Oxygen-depleted Blood away from the heart, to the Lungs, and returns oxygenated blood back to the heart. Encyclopedic description and discovery of the pulmonary circulation is widely attributed to Doctor Ibn...

 first proposed by Ibn al-Nafis.


Systemic circulation refers to the part of the circulatory system in which the blood leaves the heart, services the body's cells, and then re-enters the heart. Blood leaves through the left ventricle to the aorta, the body's largest artery. The aorta leads to smaller arteries, arterioles, and finally capillaries. Waste and carbon dioxide diffuse out of the cell into the blood and oxygen in the blood diffuses out of the blood and into the cell, blood then moves to venious capillaries, and then the venae cavae: the lower
Lower may refer to:*Lower Township, New Jersey*Lower Receiver *Lower Wick Gloucestershire, England-People:*Robert A. Lower, American Civil War Medal of Honor recipient*Cyrus B. Lower - American Civil War Medal of Honor recipient...

 inferior vena cava and the upper
Upper may refer to:* Stimulant drugs* Vamp - the part of a shoe on the top of the foot* The top part of some other object or device...

 superior vena cava, through which the blood re-enters the heart at the right atrium.


Oxygenated blood enters the systemic circulation when leaving the left ventricle
Left ventricle
The left ventricle is one of four chambers in the human heart. It receives oxygenated blood from the left atrium via the mitral valve, and pumps it into the aorta via the aortic valve.-Shape:...

, through the aortic semilunar valve. The first part of the systemic circulation is the aorta
The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...

, a massive and thick-walled artery. The aorta arches and branches into major arteries to the upper body before passing through the diaphragm, where it branches further into arteries which supply the lower parts of the body.


After their passage through body tissues, capillaries merge once again into venule
A venule is a very small blood vessel in the microcirculation that allows deoxygenated blood to return from the capillary beds to the larger blood vessels called veins. Venules range from 8 to 100μm in diameter and are formed when capillaries unite .Venules are blood vessels that drain blood...

s, which continue to merge into veins. The venous system finally coalesces into two major veins: the superior vena cava
Superior vena cava
The superior vena cava is truly superior, a large diameter, yet short, vein that carries deoxygenated blood from the upper half of the body to the heart's right atrium...

 (roughly speaking draining the areas above the heart) and the inferior vena cava
Inferior vena cava
The inferior vena cava , also known as the posterior vena cava, is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart....

 (roughly speaking from areas below the heart). These two great vessels empty into the right atrium
Right atrium
The right atrium is one of four chambers in the hearts of mammals and archosaurs...

 of the heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...


Coronary vessels

The heart itself is supplied with oxygen and nutrients through a small "loop" of the systemic circulation.

Portal veins

The general rule is that arteries from the heart branch out into capillaries, which collect into veins leading back to the heart. Portal veins are a slight exception to this. In humans the only significant example is the hepatic portal vein
Hepatic portal vein
The hepatic portal vein is not a true vein, because it does not conduct blood directly to the heart. It is a vessel in the abdominal cavity that drains blood from the gastrointestinal tract and spleen to capillary beds in the liver...

 which combines from capillaries around the gut where the blood absorbs the various products of digestion; rather than leading directly back to the heart, the hepatic portal vein branches into a second capillary system in the liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...



Because the systemic circulation is powered by the left ventricle (which is very muscular), one advantage of this form of circulation - as opposed to open circulation, or the gill system that fish use to breathe - is that there is simultaneous high-pressure oxygenated blood delivered to all parts of the body (except for the inner epithelial lining of the lungs which receive their oxygen during the exchange of the gases themselves - Dr. Matayoshi)
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