The human heart

The heart pumps blood around the body. Its structure keeps oxygenated and deoxygenated blood separate and maintains the pressure that drives circulation.

It is made of cardiac muscle, which contracts and relaxes rhythmically throughout life without tiring. A wall called the septum divides it into a right side that handles deoxygenated blood and a left side that handles oxygenated blood, and each side has a thin-walled atrium above a thick-walled ventricle.

Parts and functions

How structure suits function

The heart is built to pump blood in one direction, at the right pressure, without ever stopping. Its walls, valves and dividing septum each contribute to that.

A structure-to-function answer needs a feature, a consequence and a link to circulation. The adaptations below follow that pattern.

• The left ventricle has a much thicker, more muscular wall than the right, so it can generate the high pressure needed to pump blood all the way around the body; the right ventricle pumps only to the nearby lungs at lower pressure, which protects the delicate lung capillaries.
• The ventricles have thicker walls than the atria, so they can force blood out of the heart, while the atria only need enough force to push blood down into the ventricles.
• The atrioventricular and semilunar valves open and close as pressure changes, so blood is kept flowing in one direction and cannot flow backwards.
• The septum completely separates the two sides, so fully oxygenated blood is sent to the body without being diluted by deoxygenated blood.
• The heart is made of cardiac muscle that contracts and relaxes rhythmically without tiring, so it can keep pumping continuously throughout life.
• Coronary arteries run over the heart and supply its muscle with oxygen and glucose, so the heart has the energy for its constant pumping work.

Related processes

The heart drives a double circulation. In the pulmonary circulation, the right side pumps deoxygenated blood to the lungs, where it is oxygenated; in the systemic circulation, the left side pumps that oxygenated blood to the rest of the body.

Because blood passes through the heart twice in one full circuit, its pressure is restored after the lungs, so it reaches the body organs quickly and efficiently.

The heartbeat is the cardiac cycle repeated. The atria contract first and push blood into the ventricles; then the ventricles contract and force blood into the arteries, while the valves snap shut to give the familiar heart sounds; finally the whole heart relaxes and refills.

This coordinated sequence keeps blood moving one way.

The heart links directly to gas exchange and aerobic respiration. Blood picks up oxygen at the lungs and delivers it, along with glucose, to every respiring cell, then carries away the carbon dioxide produced.

Without the pressure the heart provides, this exchange between blood and cells could not keep pace with the body's needs.

Common labelling errors

Worked question

Question. Diagram 1 shows a section through the human heart. Chamber J receives blood returning from the lungs, chamber K pumps blood to the whole body, and vessel L carries blood away from the right side of the heart.

(a) Name chambers J and K and vessel L. (b) State whether the blood in L is oxygenated or deoxygenated, and where L carries it.

(c) Explain why the wall of chamber K is thicker than the wall on the right side of the heart. (d) Describe the role of the valves between the atria and the ventricles.

Model answer. (a) J is the left atrium; K is the left ventricle; L is the pulmonary artery. (b) The blood in L is deoxygenated; L carries it from the right ventricle to the lungs.

(c) The left ventricle pumps blood to the whole body, which needs high pressure to reach every organ, so its wall has more cardiac muscle to generate that force; the right ventricle pumps only to the nearby lungs at lower pressure, so its wall is thinner. (d) The atrioventricular valves open to let blood flow from the atria into the ventricles, and close when the ventricles contract to prevent backflow of blood into the atria, so blood keeps flowing in one direction.

Source:SRC-DSKP-EN

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