Anatomy of the Human Circulatory System

Index to this page

The Main Features

The heart and pulmonary system

The heart is located roughly in the center of the chest cavity. It is covered by a protective membrane, the pericardium.
Below: the human heart, with a schematic view of the pathway of blood through the lungs and internal organs. Oxygenated blood is shown in red; deoxygenated blood in blue. Note that the blood draining the stomach, spleen, and intestines passes through the liver before it is returned to the heart. Here surplus or harmful materials picked up from those organs can be removed before the blood returns to the general circulation. [Graphic of this hepatic portal system]

The coronary system

From the left atrium,


The coronary arteries arise at the point of maximum blood pressure in the circulatory system. Over the course of time, the arterial walls are apt to lose elasticity, which limits the amount of blood that can surge through them and hence limits the supply of oxygen to the heart. This condition is known as arteriosclerosis.


Fatty deposits, called plaque, may accumulate on the interior surface of the coronary arteries. This is particularly common in people who have high levels of cholesterol in their blood. Plaque deposits reduce the bore of the coronary arteries and thus the amount of blood they can carry.

Atherosclerosis (usually along with arteriosclerosis) may

Coronary bypass surgery uses segments of leg veins to bypass the clogged portions of the coronary arteries.

The Systemic Circulation

The remainder of the system is known as the systemic circulation. The graphic shows the major arteries (in bright red) and veins (dark red) of the system.

Blood from the aorta passes into a branching system of arteries that lead to all parts of the body. It then flows into a system of capillaries where its exchange functions take place.

In a real sense, the structures described in this page have one function only: to supply materials to — and remove materials from — the capillaries. Link to discussion of the exchanges that take place in the capillaries.

Blood from the capillaries flows into venules which are drained by veins.

Link to discussion of the control of the heartbeat.
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10 January 2011