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Higher Human Biology Unit 4 Immunology & Public Health KEY AREA 1: Non-specific Defences Higher Human Biology We are going to build on the knowledge and skills that you developed during N5 and will learn about the following Immunology & Public Health key areas : - Key Area 1 – Non-specific Defences Key Area 2 – Specific Cellular Defences Key Area 3 – Transmission and Control of Infectious Diseases Key Area 4 – Active Immunisation and Vaccination and the Evasion of Specific Immune Responses by Pathogens Physiology & Health Learning Intentions KEY AREA 1 – Non specific Immune Response a)Physical and Chemical Defences b)Inflammatory Response c)Phagocytes and Apoptosis by Natural Killer Cells 1a) Immune System Introduction Pathogens are organisms that cause disease 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: Cellular Response: Phagocytosis -Example 2: Cellular Response: Natural Killer Cells 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 1b) Physical and Chemical Defences The surface of the skin is composed of layers of closely packed epithelial cells which offer physical protection against bacteria and viruses Mucous membranes that line the digestive and respiratory tracts are also composed of epithelial cells that form a protective physical barrier Secretions from skin 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 secrete sticky mucus which traps microbes -Example 4: The epithelial lining of the stomach secretes acid which destroys microbes 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 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 resulting in blood vessels in the injured area undergoing vasodilation and capillaries becoming more permeable 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 1e) Cytokines Cytokines are cell-signalling protein molecules secreted by many types of cell including white blood cells that arrive at the site of injury/infection 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 as they are attracted by cytokines. (Phagocytes engulf pathogens by Phagocytosis) -Speedy delivery of antimicrobial proteins to the infected site (these proteins amplify the immune response) -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) 1f) Non-specific Response: Phagocytosis 1. Phagocyte detects surface antigen molecules present on a pathogen(as being ‘foreign’ or non-self), and move towards it. 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 1g) Apoptosis by Natural Killer (NK) Cells 1. NK Cells attack virus-infected cells and cancer cells in general 2. NK Cells releases molecules of a protein which forms pores in the target cell’s membrane 3. The pores allow a “signal” molecule from the NK cell to enter the target cell and trigger a genetically controlled series of events 4. The target cell then switches on a “suicide” gene, and “suicide” proteins are released 5. “Suicide” proteins function as self-destructive (degradative enzymes) which break down the cell’s DNA and vital proteins into useless fragments, causing the cell to shrink and die 6. This process of programmed cell death is called apoptosis After contact with a pathogen, Phagocytes and NK Cells release cytokines which circulate in the bloodstream and stimulate the specific immune response by activating lymphocytes 1h) Apoptosis by Natural Killer (NK) Cells Physiology & Health Questions KEY AREA 1 – Non specific Immune Response 1.Testing Your Knowledge 1 Page 311 2. Quick Quiz Q’s 1 - 4