Section B5-The living body

• Blood flows away from the heart along the arteries, through the capillaries at the organs, then back to the heart through the veins.
• As blood travels round the body it loses pressure: the arteries have the most pressure and the veins have the least pressure.
• Lots of animals e.g. fish have a single circulatory system:

• Other animals e.g. humans have a double circulatory system (like two circulatory systems one to the body and one to the lungs)
• In the double circulatory system you have a four chambered heart
• Different organs need different volumes of blood e.g. when your sitting down your muscles need 750cm(3) of blood but when you exercise your muscles get 8dm(3) of blood

The sequence of events in one complete heartbeat:

1) The blood flows into the two atria.

2) The atria contract, pushing the blood into the ventricles.

3) The ventricles contract, forcing the blood into the aorta and the pulmary artery.

Galen: ancient greek doctor, cut up animals to study the chambers in the heart. He thought blood in the arteries are made by the heart while the  blood in the veins are made by the liver and then consumed by the organs.

William Harvey: before harvey scientists still believed Galens theory. But harvey showed what the heart valves did and showed that the heart acts like a pump and that the same blood circulated around the body

 Hormones can affect your heart rate e.g. when adrenaline is released when you're in shock or danger it increases the heart rate so that your muscles have plenty of oxygen.

The hearts pacemaker:

The pacemaker cells produce a small eletric current which spreads to the surrounding muscles, which makes them contract. The two cluster of these cells are; SAN (sino-atrial node) which makes the atria contract and the AVN (atrio-ventricular node) which makes the ventricles contract. In one heartbeat the SAN produces an electric current first which makes the atria contracts. Then the current stimulates the AVN to produce an electric current which makes the ventricles contract. The atria always contract before the ventricles.

Artificial pacemakers: a little device that can be implanted under the skin and it has a wire going to the heart, which produces and electric current.

• Valve damage;  the valves can be damaged by heart attacks, infection or old age. This could mean the valves wont open properly which causes high blood pressure. Or it might allow blood to flow in both directions. This can be treated with an artificial valve from a donor or an animal.
• Hole in the heart; usually something you're born with, it's a gap in the wall separating the two ventricles or the two atria. Meaning oxygenated blood leaks to the right side and gets sent to the lungs, this is inefficient and means the heart has to pump harder to make up for the difference. This can be treated with minor surgery.
• Coronary Heart Disease (CHD); when the arteries that supply the blood to the heart are blocked by fat deposits. Normally this results in a heart attack. Can be treated by a coronary bypass surgery where a piece of blood vessel is taken from another part of the body and surgically implanted to "bypass" the blockage"

Your blood clots to prevent too much blood being lost.  Platelets clump together to clot the damage, in the clot platelets are held together by a mesh of protein.