The Circulatory System

The circulatory system consists of the heart and blood vessels including arteries, arterioles, veins and capillaries. Cardiac volumes, blood and blood pressure is also covered.

Circulatory System

What is the Human Circulatory System? The main organ of the circulatory system is the Human Heart. The other main parts of the circulatory system include the Arteries, Arterioles, Capillaries, Venules, Veins and Blood. The lungs also play a major part in the pulmonary circulation system.


Arteries are blood vessels which carry blood away from the heart. All of which, with the exception of the pulmonary artery, carry oxygenated blood. The most widely known artery within the human body is the Aorta.


Veins are blood vessels which carry deoxygenated (or very low levels of oxygen) blood back to the heart. The exception to this rule is the pulmonary vein, which carries oxygenated blood, from the lungs, back to the heart, ready to be pumped around the rest of the body.

The Heart

The heart is a strong, powerful organ, consisting of cardiac muscle. The heart pumps continuously, without resting and without becoming fatigued. Its function is to pump blood to the lungs and around the body. The heart is one of the key organs in the Circulatory System.


Capillaries are the smallest of all blood vessels and form the connection between veins and arteries. As arteries branch and divide into arterioles and continue to reduce in size as they reach the muscle they become capillaries. Here the capillaries form a capillary bed, which is a vast expanse of very small vessels forming a network throughout the muscle.

Blood pressure

The rate and distribution of blood flow through the circulatory system is variable and related to several factors including physical activity, cardiac output (the amount of blood pumped out of the heart) and venus return or the blood returning to the heart through the veins.

Cardiac Volumes

The heart beat is caused by impulses arising from two specialised groups of cells within the heart muscle. The Sino-Atrial (SA) node, situated in the wall of the right atrium initiates the beat, and the Atrioventricular (AV) node which is positioned between the ventricles and continues to distribute the wave of impulses.

Blood Composition & Function

Blood has many functions including transportation of nutrients round the body, maintaining homeostasis and the imune system. It is made up of plasma, red blood cells, white blood cells and platelets.

More Anatomy & Physiology