9.2) Heart

9.2) Heart


The heart pumps blood through the circulatory system to all the major organs of the body.



In general, blood flows into the heart from a vein, goes into an atrium, then a ventricle, and out through an artery.

The heart contains valves to prevent the blood flowing backwards:

  • the right side has a tricuspid valve (a valve with three flaps)
  • the left side has a bicuspid valve (a valve with two flaps)
  • Both sides have semi-lunar valves (at the entrances to the pulmonary artery and aorta).



  • The left ventricle has thicker walls than the right because it needs to pump blood to most of the body while the right ventricle fills only the lungs.
  • The ventricles of the heart have thicker muscular walls than the atria. This is because blood is pumped out of the heart at greater pressure from these chambers compared to the atria.
  • The septum keeps blood from the right (deoxygenated) and left (oxygenated) sides of the heart from mixing. This is important because the blood in the left ventricle is loaded with oxygen for the rest of the body to use.
  • In pumping the blood, the muscle in the walls of the atria and ventricles contracts and relaxes. The atria walls contract first and force blood into the ventricles. Then the ventricles contract and send blood into the arteries.
  • Valves prevent blood flowing backwards during or after heart contractions.


The activity of the heart may be monitored by:

  • ECG (electrocardiogram)
  • Pulse rate
  • Heart sound using a stethoscope, ‘lub-dub’ sound caused by the closure of the valves


The effect of physical activity on the pulse rate:

  • At rest, the heart beats about 70 times a minute, but varies according to age, gender and fitness.
  • An increase in physical activity increases the pulse rate, up to 200 beats per minute.
  • After exercise has stopped, the pulse rate gradually drops to its resting state, the rate depends on the fitness of the person.
  • During exercise, the muscle cells need more energy than usual. They therefore need to respire more and, as a consequence, need more oxygen and glucose, and they produce more waste, carbon dioxide.
  • If the muscle does not get enough oxygen, it will start to respire anaerobically, producing lactic acid, which cause muscle fatigue, leading to cramp.


Coronary heart disease:

  • The coronary arteries supply blood to the heart muscle. These may become blocked by a buildup of fatty plaques containing cholesterol, resulting in coronary heart disease.
  • If a coronary artery is blocked, the blood supply to part of the heart muscle is cut off. That part of the heart cannot continue to contract, causing a heart attack.


Possible Causes:

  • Lack of exercise
  • Diet high in fat and cholesterol
  • Diabetes
  • High Blood Pressure
  • Genetics
  • Stress
  • Smoking



  • Maintaining a healthy, balanced diet will result in less chance of a person becoming obese. Also be a low intake of saturated fats, so the chances of atheroma and thrombus formation are reduced.
  • Exercising increases muscle tone, good heart muscle tone leads to an improved coronary blood flow and the heart requires less effort to keep pumping.



  • Regular dose of aspirin (salicylic acid). Aspirin prevents the formation of blood clots in the arteries, which can lead to a heart attack.
  • Angioplasty and stent. Angioplasty involves the insertion of a long, thin tube called a catheter into the blocked blood vessel. A wire attached to a deflated balloon is then fed through the catheter to the damaged artery. The balloon is then inflated to widen the artery wall, freeing the blockage. Stent can be used. This is a wire-mesh tube that can be expanded and left in place.

By-pass surgery. The surgeon removes a section of blood vessel from a different part of the body, such as the leg. The blood vessel is then attached around the blocked region of artery to by-pass it, allowing blood to pass freely.

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