AQA AS Biology Unit 1 3.1.5 The Heart

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3.1.5 The Heart
Heart Structure and Function
Mammals have a double circulatory system;
Pulmonary circulation
Systemic circulation
Right Side (Pulmonary Circulation):
Receives deoxygenated blood from the body via the Vena Cava.
Pumps it to the lungs via the Pulmonary Artery where it is oxygenated.
Left Side (Systemic Circulation):
Receives oxygenated blood from the lungs via the Pulmonary Veins.
Pumps it around the body via the Aorta.
Therefore there is a much thicker muscular wall as a high pressure
needs to be generated to pump the blood around the body.
The two sides of the heart are divided by the septum.
The heart is divided into four chambers, two each side.
The upper chambers are the Atria which are smaller than the lower
chambers, the Ventricles.
The Atrioventricular (AV) valves, which are held in place by valve tendons,
prevent backflow of blood from ventricles to atria.
The semi-lunar valves prevent backflow of blood from arteries into
Cardiac Cycle

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Both atria fill with blood.
2. An electrical impulse from the sino-atrial node (SAN) [pacemaker] spreads over the atria causing atrial systole
(contraction). The impulse cannot pass directly to the ventricles due to the band of non-conducting tissue that
separates the atria and the ventricles.
3. Pressure in the atria increases forcing blood through the AV valves into the ventricles.
4. Impulse from the SAN stimulates the atrioventricular node (AVN) to produce impulses that are channelled down
into the ventricles by the bundle of His.…read more

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Angina ­ Chest pains caused by an inadequate supply of blood (and therefore oxygen) to the heart muscle.
Arteriosclerosis ­ Hardening of the arteries. Associated with old age, the blood vessel walls, particularly of the
arteries, become less elastic and more liable to rupture.
Atheroma ­ The fatty deposit that builds up under the endothelium of blood vessels. As the atheroma gets
thicker, the lumen of the artery gets smaller causing blood pressure to rise.…read more

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The build up of an atheroma is usually the result of a combination of risk factors, both environmental and genetic.
1. Diet and blood cholesterol.
Cholesterol is important in cells and your body can make its own cholesterol, but it's also found in a lot of the
foods that we eat.
Eggs, cream and fatty meat are particularly high in cholesterol, there is very little cholesterol in plants.
High levels of cholesterol in the blood lead to a build up of atheroma.…read more


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