Chapter 4- Blood and the circulation system

4.1 Blood

Blood is vital as it carries materials to cells and removes waste
Red blood cells (RBC's) are packed with haemoglobin, the oxygen carrying molecule. RBC's have no nucleus for more haemoglobin room and a greater surface area for oxygen diffusion
Oxygen is picked up and reacts with haemoglobin to produce oxyhaemoglobin
White Blood Cells (WBC's) are part of the immune system. Lymphocytes produce antibodies and phagocytes engulf microbes
Platelets are cell fragments needed for clotting, if a vessel is damaged platelets release enzymes to cause fibrinogen to turn in insoluble fibrin, which creates a net to trap
Plasma is a liquid transport medium, containing dissolved materials (glucose, aminos, urea)
Lack of haemoglobin causes anaemia- low haemoglobin means less oxygen delivered to cells, so less respiration and therefore, tired person
If someone needs a transfusion, the blood types needed to be matched, or the blood cells will clump and cause problems
Groups are determined by antigens, which are found on the surface of RBC's. The immune system produces antibodies to attack antigens and clump them

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The body uses blood to move materials, hormones and heat from sources to the body, and to move waste from cells to lungs/kidneys for disposal
Arteries carry blood away from the heart. Blood is forced into the artery from the heart. The high pressure causes the elastic walls to stretch, pushing the blood along- this is a pulse
Veins carry blood towards the heart. The walls are thin and less elastic. Body muscles press against veins to force blood to the heart, and they have valves to prevent backflow.
Capillaries are tiny blood vessels which lie close to body cells. The walls are very thin, so soluble molecule can easily diffuse into and out of the cells. The capillary network provides a massive exchange surface.
Blood pressure varies in different vessels, it is the highest in main arteries (aorta) and lowest in main veins (vena cava)
The heart muscle needs a constant supply of glucose and oxygen for aerobic respiration for energy from the coronary arteries. If the arteries is blocked by a blood clot or atheroma (fatty deposits due to high cholesterol), blood will not flow to the cardiac muscles, and the person will have a heart attack

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Symptoms of narrowed blood vessels can be the chest pains felt from angina
In a blood clot forms in the brain, brain cells do not receive oxygen and will die, causing brain damage. The resulting stroke may be mild (temporary speech loss) or severe physical disability.
The natural resting heart rate is controlled by cells in the right atrium called the pacemaker. Sometimes, due to aging or heart disease, the heart may slow down, beat irregularly or miss a beat
Scientists have developed an artificial pacemaker that fits under the skin, and stimulates the heart with electrical impulses delivered by wires
When hearts fail, a heart transplant may be needed. When patients undergo a transplant, they are attached to a heart-lung machine. It has a pump and a oxygenation system in order to circulate warm and clean blood
Other modern techniques include mechanical hearts, donor human or animal valves and, possibly, valves grown from stem cells
Any transplant needs to be tissue typed (donor antigens matched to recipient antigens), and the patient given immunosuppressant drugs, to stop rejection

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