In a human body, there are three types of circulation of blood:
Systemic (greater) circulation:
The blood flows from the left ventricle, through various parts of the body, to the right atrium, i.e. from the left to the right side of the heart through the arteries and veins which traverse the whole body. This circulation is responsible for keeping the body tissues alive by supplying a continuous stream of blood to them.
Pulmonary (lesser) circulation:
The blood flows from the right ventricle, through the lungs, to the left atrium, i.e. from the right to the left side of the heart. This circulation is responsible for oxygenation of blood. In pulmonary circulation, the blood passes through the lungs where Carbon dioxide is eliminated and Oxygen is added to blood. In this way, the pulmonary circulation makes sure that systemic circulation remains effective.
It is a part of systemic circulation, which has the following characteristics.
- The blood passes through two sets of capillaries before draining into a systemic vein.
- The vein draining the first capillary network is known as portal vein which branches like an artery to form the second set of capillaries or sinusoids. Examples: hepatic portal circulation, hypothalamo hypophyseal portal circulation and renal portal circulation.