The Composition of Blood
Red Blood Cells
They are highly specialised cells made in the bone marrow. They have a limited life span of about 100 days after which time they are destroyed in the spleen. Their one and only function is to transport oxygen.
Red Blood Cells contain haemogoblin. This is an iron-containing peotein that associates with oxygen to form oxyyhaemogoblin when there is a high concentration of oxygen in the surroundings. We say that the red blood cell is loading oxygen. When the concentration of oxygen is low, oxyhaemogoblin turns back into haemogoblin and the red blood cell unloads its oxygen.
They are highly specialised cells made in the bone marrow. They have a limited life span of about 100 days after which time they are destroyed in the spleen. Their one and only function is to transport oxygen.
Red Blood Cells contain haemogoblin. This is an iron-containing peotein that associates with oxygen to form oxyyhaemogoblin when there is a high concentration of oxygen in the surroundings. We say that the red blood cell is loading oxygen. When the concentration of oxygen is low, oxyhaemogoblin turns back into haemogoblin and the red blood cell unloads its oxygen.
As red blood cells pass through the lungs, they load oxygen. As they pass through the active tissues, they unload oxygen.
Red blood cells do not contain a nucleus. This means that more haemogoblin can be packed into each red blood cell so more oxygen can be transported. Their biconcaveshape allows efficient exchange of oxygen in and out of the cell. Each red blood cell has a high surface area to volume ratio, giving a large are for diffusion. The thinness of the cell gives a short diffusion distance to the centre of the cell. In addition, red blood cells have very thin cell surface membranes which allow oxygen to diffuse through easily.
Red blood cells do not contain a nucleus. This means that more haemogoblin can be packed into each red blood cell so more oxygen can be transported. Their biconcaveshape allows efficient exchange of oxygen in and out of the cell. Each red blood cell has a high surface area to volume ratio, giving a large are for diffusion. The thinness of the cell gives a short diffusion distance to the centre of the cell. In addition, red blood cells have very thin cell surface membranes which allow oxygen to diffuse through easily.
White Blood Cells
Phagocytes
Their main role is to protect the body against invasion by pathogens, such as bacteria and viruses.
They do this in two main ways: phagocytosis and antibody production.
About 70% of white blood cells can ingest microoganisms such as bacteria. This is called phagocytosis, and the cells are phagocytes. They do this by changing their shape, producing extensions of their cytoplasm, called pseudopodia. The pseudopodia surround and enclose the microorganism in a vacuole. Once it is inside, the phagocyte secretes enzymes into the vacuole to break the microorganism down.
Phagocytosis means 'cell eating'.
Their main role is to protect the body against invasion by pathogens, such as bacteria and viruses.
They do this in two main ways: phagocytosis and antibody production.
About 70% of white blood cells can ingest microoganisms such as bacteria. This is called phagocytosis, and the cells are phagocytes. They do this by changing their shape, producing extensions of their cytoplasm, called pseudopodia. The pseudopodia surround and enclose the microorganism in a vacuole. Once it is inside, the phagocyte secretes enzymes into the vacuole to break the microorganism down.
Phagocytosis means 'cell eating'.
Lymphocytes
About 25% of white blood cells are lymphocytes. THeir function is to make chemicals called antibodies. Antibodies are soluble proteins that pass into the plasma. Pathogens such as bacteria and viruses have telltale chemical 'markers' on their surface called antigens, which the antibodies recognise. The antibodies stick to the surface antigens and destroy the pathogen. They do this is a number of ways, for example by:
About 25% of white blood cells are lymphocytes. THeir function is to make chemicals called antibodies. Antibodies are soluble proteins that pass into the plasma. Pathogens such as bacteria and viruses have telltale chemical 'markers' on their surface called antigens, which the antibodies recognise. The antibodies stick to the surface antigens and destroy the pathogen. They do this is a number of ways, for example by:
- Causing bacteria to stick together, so that phagocytes can ingest them more easily.
- Acting as a 'label' on the pathogen, so that it is more easily recognised by a phagocyte.
- Causing bacterial cells to burst open.
- Neutralising poisons (toxins) produced by pathogens.
Some lymphocytes do not get involved in killing microorganisms straight away. Instead, they develop into memory cells. Memory cells make us immune to a disease. These cells remain in the blood for many years, sometimes a lifetime. If the same microorganims re-infects, the memory lymphocytes start to reproduce and produce antibodies, so that the pathogen can be quickly dealt with.
Their secondary immune response is much faster and more effective than the first (primary) response.
Their secondary immune response is much faster and more effective than the first (primary) response.
Vaccination
A person can be given artificial immunity to a disease without ever actually contracting the disease itself. This is done by vaccination. A person is injected with an 'agent' that carried the same antigens as a specific disease-causing pathogen. Lymphocytes recognise the antigens and multiply exactly as if that microorganism had entered the blood stream. They produce memory cells and make the person immune to the disease. Some agents used as vaccines are:
A person can be given artificial immunity to a disease without ever actually contracting the disease itself. This is done by vaccination. A person is injected with an 'agent' that carried the same antigens as a specific disease-causing pathogen. Lymphocytes recognise the antigens and multiply exactly as if that microorganism had entered the blood stream. They produce memory cells and make the person immune to the disease. Some agents used as vaccines are:
- A weakened strain of the actual microorganism, e.g. vaccines agains polio, tuberculosis (TB) and measles.
- Dead microorganisms, e.g. typhoid and whooping cough vaccines.
- Modified toxins of the bacteria, e.g. tetanus and diphtheria vaccines.
- Just the antigens themselves, e.g. influenza vaccines.
- Harmless bacteria, genetically engineered to carry the antigens of a different, disease-causing microorganism, e.g. the vaccine agains hepatitis B.
Platelets
Platelets are not whole cells, but fragments of large cells made in the bone marrow. If the skin is cut, exposure to air stimulates the platelets and damaged tissue to produce a chemical. This chemical causes the soluble plasma protein fribrinogen to change into insoluble fibres of another protein, fibrin. The fibrin forms a network across the wound, in which red blood cells become trapped. This forms a clot, which prevents further loss of blood and entry of pathogens. The clot develops into a scab, which protects the damaged tissue while new skin grows.
Platelets are not whole cells, but fragments of large cells made in the bone marrow. If the skin is cut, exposure to air stimulates the platelets and damaged tissue to produce a chemical. This chemical causes the soluble plasma protein fribrinogen to change into insoluble fibres of another protein, fibrin. The fibrin forms a network across the wound, in which red blood cells become trapped. This forms a clot, which prevents further loss of blood and entry of pathogens. The clot develops into a scab, which protects the damaged tissue while new skin grows.