Communicable diseases: non-specific animal defences Flashcards
How does the skin act as a barrier?
Cover the body and prevents access of pathogens. Skin flora of healthy microorganisms that outcompete pathogens for space on the surface. Skin produces sebum, oily substance inhibiting growth of pathogens.
How do mucous membranes prevent infection?
Many body tracts like the gas exchange system are lined with this, secreting mucus. Traps microorganisms and contains lysozymes, destroying cell walls. Also contains phagocytes.
How do lysozymes prevent infection?
In tears and urine, and acid in stomach. Destroys the pathogen walls.
What are expulsive refelxes?
Coughing and sneezing ejects pathogen-laden mucus from gas exchange system. Vomiting and diarrhoea expel contents of the gut along with any infective pathogens.
Describe the process of blood clotting and wound repair
Platelets come into contact with collagen in the skin or the wall of damaged blood vessels. Adhere and secrete substances.
Thromboplastin - enzyme that triggers a cascade of reactions forming a blood clot.
Serotonin - makes smooth muscle in the walls of the blood vessels contract, so narrow and reduce blood supply (vasoconstriction).
Clot dries out and forms a scab, keeping pathogens out. Epidermal cells below the scab begin to grow, sealing off the wound permanently, while damaged blood vessels grow.
Collagen fibres are deposited to give new tissue strength.
Describe the inflammatory response
Results in inflammation at the site of the wound - pain, heat, redness and swelling of tissue.
Mast cells are activated in damaged tissue and release chemicals called histamines and cytokines.
Histamines dilate blood vessels, localising heat and redness. Temperature prevents pathogens reproducing.
Histamine makes blood vessels leaky, plasma out, making tissue fluid. Tissue fluid causes swelling (oedema) and pain.
Cytokines attract white blood cells (phagocytes) to site. Dispose of pathogens in phagocytosis.
Describe fevers
Normal body temperature increases, as cytokines make hypothalamus overactive. Pathogens cannot reproduce and immune system works faster.
What are phagocytes?
Specialised white blood cells that engulf and destroy pathogens. There are neutrophils and macrophages.
Describe the stages of phagocytosis
1) Pathogens produce chemicals that attract phagocytes.
2) Phagocytes recognise the antigens on the surface of the pathogen (non-human proteins).
3) Phagocyte engulfs the pathogen and forms a vacuole called a phagosome.
4) Phagosome combines with a lysosome to from a phagolysosome.
5) Enzymes from the lysosome digest and cause lysis of the pathogen.
Difference between neutrophils and macrophages
Macrophages take longer to engulf the pathogen, as the process is more complex. Macrophage has digested a pathogen, it combines with antigens from the pathogen surface membrane, with glycoproteins in the cytoplasm. Called the major histocompatibility complex (MHC).
Role of MHC
The complex moves these pathogens antigens to the macrophages own surface membrane, becoming an antigen presenting cell (APC). These antigens now stimulate other cells involved in specific immune system response.
How are blood cells counted?
Haemocytometer are used. Have different sized grids, to look at the size and shape of blood cells, as well as how many in the quadrat-like slide. Often stained to add contrast to the nuclei of lymphocytes, so easy to identify. Identify the number can show a specific or non-specific immune response.
Role of cytokines in phagocytosis
Act as cell-signalling molecules, informing other phagocytes of a pathogen being present. Stimulates inflammation and phagocytes to move to the site of infection. Increase body temp. and stimulate immune system.
Role of opsonins
Chemicals that bind to pathogens and ‘tag’ them so easily recognised. Phagocytes have receptors on the plasma membranes that bind to common opsonins, and phagocyte engulfs pathogen. Antibodies immunoglobulin G (IgG) and immunoglobulin M (IgM) have best effect.
