The Circulatory System

The circulatory system consists of the heart and blood vessels. Its function is to transport blood around the body.


Circulatory system anatomy

There are three main parts to the circulatory system. These are the systemic, pulmonary and coronary circulation. Systemic circulation carries blood around the body. Pulmonary circulation carries blood to the lungs. Coronary circulation provides the heart with its own blood supply.

Learn more about the structure of the circulatory system.

The Heart

The heart is the main organ of the circulatory system. It pumps blood to the lungs and around the body. It pumps continuously, without resting and without fatigue. Its function is to pump blood to the lungs and around the body.

Learn more about the human heart.

Heartbeat & Cardiac Volumes

The heartbeat 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.

Learn more about the heartbeat.

The Heart Conduction System

The conduction system of the heart refers to how the heart contracts. Here we explain how electrical impulses ensure it beats regularly including specific parts of the heart involved such as the Bundle of His, Synoartial node as well as exam-type questions and quizzes.

Learn more about the heart conduction system.

Blood Pressure & the circulatory system

Blood pressure is the rate and distribution of blood flow through the circulatory system. It varies depending on physical activity, cardiac output (the amount of blood pumped out of the heart) and venous return, (blood returning to the heart through the veins).


Arteries carry oxygenated blood away from the heart, except the pulmonary artery which carries deoxygenated blood to the lungs. A good way to remember this is when you see the word ‘pulmonary’, it is usually something related to the lungs. The largest artery in the human body is the Aorta which carries blood away from the heart to the rest of the body.


Capillaries are the smallest of all blood vessels and form the connection between veins and arteries.


Veins carry deoxygenated blood back to the heart (or blood very low levels of oxygen). The exception is the pulmonary vein which carries oxygenated blood, from the lungs, back to the heart.

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