Overview
The heart consists of four chambers in which blood flows. Blood enters the right atrium and passes through the right ventricle. The right ventricle pumps the blood to the lungs where it becomes oxygenated. The oxygenated blood is brought back to the heart by the pulmonary veins which enter the left atrium. From the left atrium blood flows into the left ventricle. The left ventricle pumps the blood to the aorta which will distribute the oxygenated blood to all parts of the body.
Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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The circulatory system (CCEA)
Blood is pumped away from the heart at high pressure in arteries, and returns to the heart at low pressure in veins. The human circulatory system is a double circulatory system.
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Biology (Single Science)
Body systems
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The heart
The heart is a unidirectional pump.
Valves are present to prevent the backflow of blood.
The right side pumps deoxygenated blood (low in oxygen and high in carbon dioxide) to the lungs.
The left side pumps oxygenated blood (high in oxygen and low in carbon dioxide) to the organs of the body.
- Deoxygenated blood enters the right atrium from the vena cava.
- Blood moves into right ventricle.
- Blood is pumped into the pulmonary artery.
- The pulmonary artery carries deoxygenated blood to the lungs.
- The blood becomes oxygenated in the lungs.
- Oxygenated blood leaves the lung via the pulmonary vein.
- Blood enters the left atrium.
- Blood moves into the left ventricle.
- Blood is pumped into the aorta, which carries oxygenated blood around the body.
This unidirectional flow of blood through the heart shows that mammals have a double circulatory system.
This means blood travels through the heart twice in one circulation of the body.
Ventricular walls are thicker than atrial walls because the ventricles have to pump blood further.
The left ventricle wall is thicker than the right because it pumps blood around the body while the right pumps blood to the lungs, located close to the heart.
The following arteries and veins transport blood to and from some of the body’s organs:
| Vena cava | Carries deoxygenated blood from the body back to the heart. |
| Pulmonary artery | Carries deoxygenated blood from the heart to the lungs. |
| Pulmonary vein | Carries oxygenated blood from the lungs to the heart. |
| Aorta | Carries oxygenated blood from the heart around the body. |
| Hepatic artery | Carries oxygenated blood to the liver. |
| Hepatic vein | Carries deoxygenated blood back to the heart. Carries digested food (glucose and amino acids) from the liver around the body. |
| Hepatic portal vein | Carries digested food from the small intestine to the liver. |
| Renal artery | Carries oxygenated blood (also rich in urea) to the kidneys for excretion. |
| Renal vein | Carries deoxygenated blood (also low in urea as it has been purified in the kidney) back to the heart. |
The oxygen and glucose carried in oxygenated blood is used for respiration in the body’s cells.
The coronary arteries provide the heart muscle with the glucose and oxygen it needs for respiration.
These are small blood vessels that branch off the aorta and can be seen on the external surface of the heart.
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