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The function of the Circulatory System


The blood circulatory system delivers oxygen and nutrients to all cells in the body. This system consists of the heart and blood vessels present in every corner of the body, each one with its own function. Arteries are the vessels which carry blood away from the heart and veins are the vessels which carry blood back to the heart. The arteries going smaller and smaller end up in a network of tiny blood vessels1.

There are two blood circulatory systems in the body, with different functions: 
1. Systemic Circulation
2. Pulmonary Circulation

The systemic circulation provides cells, tissues and organs with blood so that they can have vital substances and oxygen. Pulmonary Circulation is where fresh oxygen enters the blood and carbon dioxide is released from the blood2

The time when the heart relaxes between the two heartbeats is the time when the cycle of blood circulation starts. The cycle starts with the flow of the blood from both atria to the both ventricles which expands then. In the next phase, blood is pumped into the large arteries from both of the ventricles. Blood travels from arteries to the capillaries where the exchange of nutrients, oxygen, carbon dioxide and other substances occur between the capillaries and the cells. The low oxygen blood is then collected to the veins and travels to the right atrium3.

Now, it’s the turn of pulmonary circulation. From the right ventricle, blood travels through the pulmonary artery to the capillaries. The capillaries form a fine network around the alveolar sac (basic functional unit of the lung) and here the exchange of oxygen and carbon dioxide occurs which means fresh oxygen enters the blood and carbon dioxide leaves the body4.

The cardiovascular circulation is maintained by precise regulation so that every single cell can be supplied with an appropriate supply of oxygenated blood. For this purpose, two parameters are checked by sensory receptors.
1. The pressure in the arterial system is checked by barosensory receptors.
2. The level of oxygen and carbon dioxide is checked by chemosensory receptors5.

The baroreceptors are located in the heart and major blood vessels; the chemoreceptors are located in the carotid bodies which are situated at the bifurcation of common carotid artery6 7.

6. H.all J, Guyton A. Guyton And Hall Review Of Physiology. Edinburgh: Elsevier Saunders; 2005:161-193.
7. Ganong W. Review Of Medical Physiology. New York: Lange Medical Books; 2005:555-570.

Topics: Blood Circulatory System

Dr. Owais Amin

Written by Dr. Owais Amin