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The components of blood
– Plasma, - mainly water, has a wide range of dissolved of dissolved substances, Fibrinogen vital for clotting
Erythrocytes – Biconcave discs, 5 million per 1 mm of blood, formed in the bone marrow and short bones. Contain haemoglobin, red in colour. Lifespan 120 days
Leucocytes – much larger, about 4000 to 11000 per mm of blood, formed in bone marrow of long bone and femur in the leg, lymphocytes are however formed in the lymph glands and spleen. Defence
Platelets – tiny fragments of cells called megakaryocytes. Involved in clotting
The main functions of blood
• Transport of food substances to the cells as needed
• Transport of excretory products e.g. CO2 and urea to the cells that excreate them
• Transport of hormones
• Help to maintain a steady body temperature by distribution of heat
• Acts as a buffer to pH changes
•transports digested food products (eg glucose and amino acids) from the small intestine to all the parts of the body where they are needed either for immediate use or storage
red blood cells
transport oxygen from the lungs to all the cells. They are well adapted for transporting oxygen. The shape of the cells – a biconcave disc – means that they have a large surface area to volume ratio, so oxygen can diffuse into and out of them rapidly. Having no nucleus leaves all the space inside the cells for the haemoglobin molecules that carry the oxygen.
white blood cells defend against disease in two main ways:
• Some types make antibodies which destroy pathogens or antitoxins which neutralise the poisons (toxins) made by pathogens. Once the body has encountered a pathogen, these white cells can make antibodies to this pathogen very quickly if it invades again. This is the basis of the body’s immunity to diseases.• Some white blood cells engulf and digest pathogens in a process known as phagocytosis
Substances move between the plasma or red blood cells and the body cells by ...
diffusion or active transport.
How well adapted are Erythrocytes
• Biconcave shape enhances more surface area to volume ratio • No nucleus mean more space created to pack haemoglobin• Numerous on the blood, 5 mill per mm of blood
• Leucocytes – some makes antibodies which destroy pathogens • Some engulf the pathogen itself. (phagocytosis.)
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