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Blood circulation is the flow of blood from the heart to all body parts and back to the heart.Blood circulation or circulatory system, also called cardiovascular system, is one of three mainsystems in human body which consist of organs and tissues.

The cardiovascular systems of humans are closed, so the blood never leaves the network of bloodvessels. But oxygen and nutrients diffuse across blood vessel layers and enter interstitial fluid,which carries it to the target cells and carbon dioxide and wastes in the opposite direction. The human blood circulation consists of two circulations namely the pulmonary circulation and systemic circulation:-

1. Pulmonary circulation is the movement of blood from the heart, to the lungs, and back to theheart again. This is just one phase of the overall circulatory system. In this type of circulation,the blood flows from the right ventricle to the lungs and from the lungs to the left auricle. In thepulmonary circulation, the blood circulates to and from the lungs, to release the carbon dioxideand pick up new oxygen.

In the pulmonary circulation, blood from all body parts (except the lungs) enters the right auriclethrough vena cava. From the right auricle the blood descends into the right ventricle through the tricuspid valve.

When the ventricle contracts, the blood is pushed into the pulmonary artery thatbranches into two main parts: one going to the left lung, and another to the right lung. The fresh,oxygenated blood returns to the left auricle of the heart through the pulmonary vein.

2. Systemic circulation is the flow of blood between the heart and the body parts. In this particular circulation, the blood flows from the left ventricle to different parts of the body and from different parts of the body to the right auricle. The systemic circulation supplies nourishment toall of the tissues located throughout your body, with the exception of the heart and lungs because they have their own systems.

Systemic circulation is a major part of the overall circulatory system. In this circulation, the blood circulates into the body’s systems, bringing oxygen to all itsorgans, structures and tissues and collecting carbon dioxide waste.

The systemic cycle begins when the oxygenated blood coming from the lungs enters the leftauricle. As the chamber fills, it presses open the bicuspid valve and the blood flows down intothe left ventricle. When the ventricles contract during a heartbeat, the blood on the left side isforced into the aorta.

This largest artery of the body is an inch wide. The blood leaving the aortabrings oxygen to all the body’s cells through the network of ever smaller arteries and capillaries.The used blood from the body returns to the heart through the network of veins.

All of the blood from the body is eventually collected into the two largest veins: the superior vena cava, which receives blood from the upper body, and the inferior vena cava, which receives blood from thelower body region. Both venae cavae empty the blood into the right auricle of the heart.

The process by which blood passes through the heart twice before it returns to the other parts ofthe body is called double circulation.

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