Blood Vessels and the Blood

• Arteries - carry blood away from the heart
• Capillaries - Small blood vessels that connect arteries and veins.
• Veins - carry blood to the heart at a lower pressure, and have a thinner wall than arteries
• Arteries carry blood under pressure (high) so the artery walls are strong and elastic
• Artery walls are thick compared to the size of the hole down the middle of the artery
• Contain thick layers of muscle to make them strong and elastic fibres to allow them to stretch and spring back
• Capillaries are really small (one cell thick)
• arteries branch into capillaries
• capillaries are too small to see
• Capillaries carry blood really close to every cell in the body to exchange substances with them
• Capillaries have permeable walls so substances can diffuse in and out
• Capillaries supply food and oxygen and take away waste like CO2
• Veins take blood back to the heart
• Capillaries eventually join up to form veins
• The blood in veins is at a lower pressure in the veins so the walls dont need to be as thick as artery walls
• Veins have bigger lumens (holes) than arteries to help the blood flow despite lower pressure
• veins also have valves to keep blood flow in the right direction
• Rate of blood flow = volume of blood / number of minutes
• Red blood cells carry oxygen from the lungs to the body cells.
• Red blood cell shape is a bioncave disc (doughnut like) - gives a large surface area for absorbing oxygen
• red blood cells do not have a nucleus which allows more room to carry oxygen
• red blood cells carry a red pigment called haemoglobin
• In the lungs,haemoglobin binds to oxygen to become oxyhaemoglobin. in body tissues the reverse happens - oxyhaemoglobin splits into oxygen and haemoglobin to release oxygen into the cells
• White blood cells defend against infection
• some white blood cells can change shape to ingest unwelcome microorganisms in a process called phagocytosis
• other white blood cells produce anti bodies to fight microorganisms as well as anti toxins to neutralise any toxins produced by the microorganisms
• unlike red blood cells white blood cells have a nucleus
• Platelets help clot blood
• platlets are small fragments of cells,they have no nucleus
• platlets help blood clot at a wound - to stop blood pouring out and microorganisms getting in
• lack of platlets can cause excessive bleeding and bruising
• plasma is a pale straw coloured liquid that carries most things in the blood
• red and white blood cells and platlets are carried in the plasma
• plasma also carries nutrients such as glucose and amino acids which are soluble products of digestion which are absorbed from the gut and taken to the lungs
• plasma carries CO2 from the organs to the lungs,urea from the liver, hormones,proteins, antibodies and anti toxins produced by the white blood cells