circulatory system - blood

• red blood cells also known as erythrocytes carry oxygen from the lungs to the rest of the body.
• red blood cells are adapted by having a biconcave disc shape to increase the surface area for absorbing oxygen . not having a nucleus to allow more room for oxygen .
• red blood cells contain haemoglobin and in the lungs these bind to oxygen to become oxyhaemoglobin. in body tissue oxyhaemoglobin splits into haemoglobin and oxygen to release oxygen to cells
• white blood cells defend again infections. phagocytes engulf pathogens and destroy them this is called phagocytosis. lymphocytes produce antibodies that bind on the specific antigens of the pathogens to kill them
• lymphocytes can also produce antitoxins to fight off toxins produced my microorganisms
• when you have an infection your body produces more white blood cells so to detect infection you can take a blood test to show if you have a high white blood cell count
• platelets help blood clot around a wound to help stop you from bleeding out and microorganisms getting in. these are small fragments of cells and don't contain a nucleus. lack of platelets causes excessive bleeding an bruising
• plasma is a pale yellow liquid that carries about everything e.g. red and white blood cells and platelets. glucose and amino acids. carbon dioxide from organs to lungs. urea, hormones and proteins
• there are 3 different types of blood vessels: arteries, vein and capillaries
• arteries carry blood away from the heart. these pump blood out at high pressures. the walls are strong and elastic. the walls are also thick compared to the lumen to withstand the pressure. they have a thick layer of muscle to make them strong.
• arteries branch off into capillaries. these are really small and narrow to squeeze into gaps between cells and carry blood really close to every cell in the body to exchange substances. they have permeable walls so substances can diffuse in and out.
• capillaries supply food and oxygen and take away waste such as carbon dioxide. the walls are once cell thick to increase the rate of diffusion by decreasing the distance
• veins carry blood towards the heart. these are made up of joint up capillaries. the blood is at a lower pressure so the walls aren't as thick as in the arteries. they have a bigger lumen to help blood flow despite the pressure. they also have valves so the blood flows in the right direction.