Biology 2

The circulatory system consists of the blood vessels, blood and heart. The heart is a muscular organ that pumps blood round the body with 2 pumps. The right pump forces deoxygenated blood to the lungs where it picks up oxygen and loses carbon dioxide. The oxygenated blood then returns to the heart and is pumped around the rest of the body by the left pump. 

The heart has four chambers:

- the upper chambers are called the atria, they recieve blood from the vena cava on the right and pulmonary vein on the left. The atria contract to move blood to the lower chambers

- the lower chambers are called the ventricles, they contract to force blood into the pulmonary artery on the right and into the aorta on the left. 

Valves in the heart prevent blood from flowing in the wrong directing. 

Arteries:

- carry blood away from the heart

- have thick walls containing muscle and elastic

Veins:

- have thinner walls than arteries

- have valves along them to prevent backflow of blood

Capillaries:

- they are narrow, thin walled vessels

- they carry blood through organs to allow the exchange of substances

The heart keeps the blood flowing through the blood vessels so if they are blocked or too narrow the blood will not effectively flow depriving organs of nutrients and oxygen they need. 

Stents can be used to keep blood vessels open. They are inserted with a balloon attached which will be inflated to open the stent, the balloon will then be removed and the stent will keep the artery open and the blood flowing. 

Leaky valves means the blood could flow in the wrong direction. Artificial or animal valves can be inserted in the heart to replace damaged ones. 

Blood plasma contains red blood cells, white blood cells and platelets. Blood transports dissolved food molecules from the small intestine to other organs, carbon dioxide from the organs to the lungs and urea from the liver to the kidneys.

Red blood cells are concave discs that contain haemoglobin. They carry oxygen from your lungs to the tissues and cells that need it to form oxyhaemoglobin.

White blood cells are part of the bodys defence against infection and disease. They form anti-bodies that recognise the antigen so they engulf and digest pathogens.

Platelets are small fragments of cells. They help the blood to clot at the site of a wound by producing a network or protein threads that caprture red blood cells to help it clot. This stops the bleeding and forms a scab.

Blood from a donor can be seperated into cells and plasma however it must be refrigerated. The blood can be given in a transfusion to increase your blood volume and carry oxygen however it must match your blood exactly and donors are uncommon.

Artificial blood such as perfluorocarbons may be used,it doesn't need to be refrigerated or match your blood type. However it is very expensive and doesn't carry as much oxygen as normal blood. Some blood can cause side effects. 

Hearts from a donor are very uncommon so there is a long waiting list but can be used to save your life. They need to match your blood type exactly and they can easily be rejected by your bodies immune system.

Artificial hearts have no waiting list, they dont have to match your blood type and they will not be rejected. However, they are very expensive, there have been problems with clotting and they don't last very long.