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Higher Human Biology

Higher Human Biology. Unit 3B Immunology. KEY AREA 1B: Non-specific Body Defences. 1a) Immune System Introduction. Pathogens are organisms that cause disease, e.g. bacteria, viruses

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Higher Human Biology

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  1. Higher Human Biology Unit 3B Immunology KEY AREA 1B: Non-specific Body Defences

  2. 1a) Immune System Introduction Pathogens are organisms that cause disease, e.g. bacteria, viruses The human body defends itself against pathogens, toxins (produced by living things) and cancer cells through the immune system Immunity is the ability of the body to resist infection by a pathogen or destroy the organism if it succeeds in invading and infecting the body First line of defence (Non-specific) Example 1: Skin to act as a physical barrier to pathogens Example 2: Secretion of stomach acids to kill microbes Example 3: Secretion of mucus by the trachea to trap microbes Second line of defence (Non-specific) Example 1: Inflammatory response Example 2: Cellular Response: Phagocytosis Third line of defence (Specific) Example 1: Response by T-Lymphocytes from the Thymus Gland Example 2: Production of antibodies by B-lymphocytes from Bone Marrow

  3. 1b) Physical and Chemical Defences The surface of the skin is composed of layers of closely packed epithelial cells which form a physical barrier against invading pathogens Mucous membranes that line the digestive and respiratory tracts are also composed of epithelial cells that form a protective physical barrier Secretions provide chemical defence against invasion:- • Example 1: Sweat glands and sebaceous glands in the skin keep the skin at a pH that is too low for most microbes to survive • Example 2: Tears and saliva contain the enzyme Lysozyme which digests the cell walls of bacteria and destroys them • Example 3: Mucous membranes (respiratory system) secrete sticky mucus which traps microbes • Example 4: The epithelial lining of the stomach secretes acid which destroys microbes

  4. 1c) Inflammatory Response When the body suffers a physical injury such as a cut and/or invasion by microbes, it responds by a localised defence mechanism called an inflammatory response at the affected site

  5. 1d) Inflammatory Response: Mast Cells & Histamine Mast cells:- - are produced from the same stem cells as white blood cells - they are present in connective tissue throughout the body - they release histamine Histamine is a chemical that causes blood vessels to vasodilate (become wider) and capillaries to become more permeable After injury, mast cells are activated and release large quantities of histamine

  6. 1e) The Inflammatory Response The additional blood supply makes the injured area red and inflamed, and it swells up due to the stretched capillary walls becoming more permeable which causes them to leak fluid into neighbouring tissues During the inflammatory response, increased blood flow and permeability of capillary walls bring about the following beneficial effects:- • An accumulation of phagocytes to the damaged tissue (Phagocytes engulf pathogens by Phagocytosis) • Rapid delivery of blood-clotting chemicals (clotting elements) to the injured area (Coagulation of blood stops the loss of blood, prevents further infection and marks the start of the tissue repair process)

  7. 1f i) Non-specific Response: Phagocytosis Phagocytes are white blood cells that recognise pathogens and destroy them by phagocytosis Phagocytes release chemicals called cytokines Cytokines are protein molecules that act as a signal to specific white blood cells causing them to accumulate at the site of infection

  8. 1f ii) Non-specific Response: Phagocytosis stages 1. Phagocyte detects the pathogen 2. Phagocyte engulfs the pathogen (bacterium) by infolding of the cell membrane to create a vacuole. 3. Lysosomes, are cell organelles which contain digestive enzymes, present in the phagocyte’s cytoplasm fuse with the vacuole and release enzymes to digest the ‘foreign’ pathogen 4. The breakdown products are adsorbed by the phagocyte 5. Once the pathogen is digested the Phagocyte releases cytokines which attract more phagocytes to the infected area to continue the battle against the pathogens 6. Dead bacteria and phagocytes accumulate at the infected site as a pus

  9. Immunology Questions KEY AREA 1B – Non specific Immune Response • Testing Your Knowledge 1 Page 311 Q 1 – 4 (except 4a) • Quick Quiz

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