GCSE Biology heart notes

Arteries carry blood away from the heart. They have to cope with high blood pressure so they have a thick wall made of elastic muscle fibres.

Veins carry blood to the heart. They have lumen which is much bigger compared to the thickness to the walls. They also have valves to prevent the backflow of blood.

Capillaries are the only blood vessels that have thin permeable walls to allow the exchange of substances between cells and the blood.

In the long term high blood pressure is dangerous because the blood vessels can weaken and eventually burst. If this happens in the brain it could lead to brain damage or stroke. 

Low blood pressure means the blood doesn't circulate efficiently, so some parts of the body are deprived of glucose and oxygen. This can lead to dizziness, fainting and cold hands and feet. Pressure may drop in the kidneys, leading to kidney failure. 

Factors that can lead to high blood pressure:  Excess weight- the circulatory system has to work harder to pump blood around the body of a person who is overweight.  High stress levels Excess alcohol A diet which is high in saturated fat, sugar and salt. Too much salt can raise blood pressure, whilst too much saturated fat can lead to a build up of cholesterol in the arteries forming plaques. This plaque bulges into the lumen, restricting or blocking blood flow through the arteries, increasing the risk of heart attack.  Smoking- CO takes place of oxygen in the haemoglobin so the oxygen-carrying capacity of the blood is greatly reduced. The heart rate and pressure increases in order to compensate. Plus, nicotine increases heart rate. 

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