The heart
Blood is pumped around the body by the Muscular organ that pumps blood around the body..
The heart has four chambers - two In the heart, the atria (plural) are the upper chambers which collect blood returning from the body (right atrium) or from the lungs (left atrium). and two The lower chamber of the heart that receives blood from the atrium and pumps it into arteries..
Blood enters the heart through the atria. Blood from two One of the two veins that carries deoxygenated blood to the heart from the body systems. enters the right atrium. Blood from the One of the four veins that carries oxygenated blood to the heart from the lungs. enters the left atrium. The atria fill, followed by the ventricles. Blood is prevented from flowing back into the atria by heart valves.
Blood leaves the heart in the body's main artery - the Main artery which carries oxygenated blood from the heart in mammals. - from the left side, and the The artery which carries deoxygenated blood from the heart to the lungs., from the right.
Double circulation
Humans have a double circulatory system. The heart pumps blood through two circuits:
- the The part of the circulatory system that involves the right side of the heart, the lungs, and the blood vessels that connect them together.
- the The part of the circulatory system that includes the left side of the heart, the rest of the body apart from the lungs, and the blood vessels that connect them together.
The pulmonary circulation transports blood to the lungs. At the lungs:
- Gaseous element making up about 20% of the air, which is needed by living organisms for respiration.The movement of molecules from an area of higher concentration to an area of lower concentration. into the blood from the Tiny air sacs in the lungs, where gas is exchanged during breathing. - the blood becomes oxygenated
- A gaseous compound of carbon and oxygen, which is a by-product of respiration, and which is needed by plants for photosynthesis. diffuses from the blood into the lungs
The systemic circulation transports:
- oxygen and nutrients to the body
- carbon dioxide and other wastes away from cells
The systemic circulation is under high pressure - it has to deliver blood to the extremities of the body.
The pulmonary circulation is under lower pressure, because:
- blood is delivered to the lungs only, which are very close to the heart
- in a healthy person, this lower pressure is optimum for the diffusion of gases
Circulating blood
Blood passes through the heart twice in one complete circulation of the body.
Following the blood through one complete circulation of the body:
Image caption, 1. Deoxygenated blood from the body enters the right atrium
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Note that although this is shown as a sequence, the atria contract in unison, and when full, the ventricles also contract in unison.
Part of the blood is being delivered to the body, while the remainder of the blood is being transported to the lungs. This means that oxygen can be picked up from the lungs, while at the same time, blood is also being delivered to the body.
Listen to a podcast about the circulatory system with Dr Alex Lathbridge.
Listen to the full series on BBC Sounds.
Listen to a podcast about the circulatory system with Dr Alex Lathbridge.
