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Human Physiology (6.3 Defence against infectious diseases (Blood clotting,…

- - - - These clotting factors set off a cascade of reactions in which the product of each reaction is the catalyst of the next reaction.
    - - This allows the remaining polypeptide to bind to others forming long protein fibres called fibrin. Fibrin forms a mesh of fibres across wounds. Blood cells are caught in the mesh and soon form a semi solid clot.
  - - - A lymphocyte can only make one type of antibody so a huge number of different lymphocyte types is needed. Each lymphocyte puts some of the antibody that it can make into its cell surface membrane with the antigen combing site projecting outwards.
        
        When a pathogen enters the body its antigens bind to the antibodies in the cell surface membrane of one type of lymphocyte.
        
        When antigens bind to antibodies on the surface pf a lymphocyte this lymphocyte becomes active and divides by mitosis to produce a clone of many identical cells.
        
        The cells produced by mitosis are plasma cells. They produce large quantities of the same antibody. These anitbodies then destroy the pathogen. This is known as specific immunity. After an infection most lymphocytes used to produce antibodies disappear, but some persist as memory cells.
  - - - small cuts or tears in the vagina, penis, moth, intestine during vaginal, anal or oral sex
        
        Traces of blood on hypodermic needles shared by drug abusers
        
        Across the placenta from a mother to a baby or through cuts during childbirth or in milk during breast feeding.
        
        In transfused blood or with blood products.
  - - - e.g. penicillium fungus prodcues penicillin to kill bacteria
        
        Antibiotics work by blocking processes that occur in prokaryotic cells but not eukaryotic cells.
- - - - lipids - Lipase -> fatty acids and glycerol
      - polypeptides - endopeptidase -> shorter peptides
      - starch - amylase -> maltose
      - The pancreas secretes these enzymes into the lumen of the small intestine.
  - - - in which nutrients pass down the concentration gradient between phospohlipids in the membrane
    - - in which nutrients pass down the concentration gradient through specific channel proteins in the membrane.
    - - in which nutrients are pumped through the membrane against the concentration gradient by specific pump proteins.
    - - in which small droplets of the fluid are passed through the membrane by means of vesicles.
- - - - Convey blood pumped out at high pressure by the ventricles of the heart. They carry the blood to tissues of the body.
      - Tough outer coat.
      - Thick wall to withstand the high pressures
      - Narrow lumen to help maintain the high pressures.
      - Thick layer containing elastic fibres that maintain high pressure between pumping cycles and muscle that contracts and relaxes to adjust the diameter of the lumen,
    - - Carry blood through tissues. They have permeable walls that allow exchange of materials between the cells of the tissue and the blood in the capillary.
      - Wall consists of a single layer of thin cells so the distance for diffusion in or out is small.
      - Pores between cells in the wall allow some of the plasma to leak out and form tissue fluid. Phagocytes can also squeeze out.
      - Very narrow lumen - only about 10micrometres across so that capillaries fit into small spaces. Many small capillaries have a large surface area than fewer wider ones would.
    - - Collect blood at low pressure from the tissues of the body and return it to the atria of the heart.
      - Thin layer of tissue with few or no elastic fibres or muscle as blood flow is not pulsatile.
      - Thin wall allows the vein to be pressed flat by adjacent muscles, helping to move the blood.
      - Outer coat is thin as there is no danger of veins bursting.
      - Wide lumen is needed to accommodate the low pressure slow flowing blood. Valves are present at intervals in veins to prevent back flow.
  - - - The right side pumps deoxygenated blood to the lungs via the pulmonary artery. Oxygenated blood returns to the left side of the heart in the pulmonary vein. The left side then pumps this blood via the aorta to all organs of the body apart from the lungs. Deoxygenated blood is then carried back to the right side of the heart in the vena cava.
  - - - Blood supplied by coronary arteries. Provides oxygen and nutrients in order for aerobic respiration which provides energy for cardiac muscle contraction