Non-specific animal defense Flashcards
(18 cards)
What are the two lines of defence in animals?
- Non-specific (innate) immunity
- Acquired specific immunity (the specific immune response)
What are the two levels to non specific immunity?
- Primary defences => to stop the pathogen from entering the body’s system
- Secondary internal defences => killing the pathogen when it has entered the system
What are the 2 types of surface on the body exposed to the exterior environment?
- Cutaneous membrane
- Mucous membrane
What is mucous membrane?
Membranous linings of body tracts, body cavities and tubular organs that secrete mucus
What are the barriers to the entry of pathogens in humans?
Skin:
- Covers the body and prevents entry of pathogens => impervious to microbes
- It has a skin flora of healthy microorganisms that outcompete pathogens for space on the body surface
- Secretes sebum, an oily substances that inhibits the growth of pathogens
- Sweat provides a chemical barrier
Mucous membranes:
- The respiratory, digestive, urinary and reproductive tract are lined by mucous membranes that secrete stick mucus
- This traps microorganisms and contains lysozymes, which destroy bacterial and fungal cell walls
- Mucus also contains phagocytes, which remove remaining pathogens
- Lysozymes in tears and urine, and the acid in the stomach, also help to prevent pathogens getting into our bodies
How do expulsive reflexes keep pathogens out?
- Coughing and sneezing => these reflex actions prompted by pathogens irritating the lining of airways
- They eject pathogen-laden mucus from the gas exchange system
- Vomiting and diarrhoea expels the contents of the gut along with any infective pathogens and toxins from the stomach
Why does blood clot?
- To stop bleeding
- To prevent entry of pathogens
How does blood clotting and wound repair work?
- When you the tissue is damaged pathogens can enter the body
- Platelets are activated by the exposed collagen fibers in the damaged vessel wall
- Platelets secrete serotonin, which makes the smooth muscle in the walls of the blood vessels contract, so they narrow and reduce the supply of blood to the area
- Platelets also secrete the enzyme thromboplastin
- Thromboplastin, in the presence of calcium ions (Ca²⁺) from the plasma, catalyses the reaction of prothrombin (an inactive enzyme) into its active form: thrombin
- Thrombin catalyses the reaction of fibrinogen, a soluble plasma protein, into fibrin, which is insoluble
- Fibrin fibres form a mesh over the wound trapping red blood cells and platelets
- Bleeding stops
- Clot dries out, forming a hard, tough scab that keeps pathogens out
What occurs below the scab?
- Epithelial cells divide by mitosis sealing wound permanently
- Damaged capillaries reform
- Collagen fibres are deposited by fibroblasts to strengthen new tissue
- The scab sloughs off when epidermis reaches normal thickness and the wound is healed
- Enzyme plasmin is released to degrade and dislodge cut
What is an inflammatory response? And what is it characterised by?
A localised response to pathogens (or damage or irritants) resulting in inflammation at the site of a wound as protection from infection/injury
It is characterised by:
- Pain and tenderness
- Heat
- Redness
- Swelling of tissue
What is the process of the inflammatory response?
- The inflammatory response is triggered by damaged cells/tissue entry of pathogens
- This triggers mast cells to release histamines
- Histamines make the blood vessels dilate (vasodilation), increasing blood flow to area, capillary walls become more permeable
- This makes it easier for phagocytes to leave the blood
- This causes localised heat and redness
- The raised temperature helps prevent pathogens reproducing
- Masy cells secrete cytokines which attract phagocytes to the site
- They dispose of the pathogens by phagocytosis
What are some examples of primary non-specific defences?
- Physical barriers
- Expulsive reflexes
- Blood clotting and wound repair
- Inflammatory response
What are some examples of secondary non-specific defences?
Phagocytosis
What is the process of phagocytosis?
- The phagocyte binds to the pathogen. This is enabled by opsonins
- Cytoskeleton moves the cytoplasm and plasma membrand around the pathogen forming pseudopodia and engulfing the pathogen/bacteria
- The bacteria becomes enclosed in a vacuole called a phagosome. The phagosome fuses with a lysosome forming a phagolysosome
- Lysozyme (hydrolytic enzyme) from the lysosome come into contact with the bacteria within the phagolysosome
- Bacteria is hydrolysed/digested into small fragments and soluble monomers
- Monomers are absorbed into the cytoplasm of the phagocyte across the phagolysosome membrane
- Fragments of Antigen are displayed on the surface of the macrophage, making it an Antigen Presenting Cell (APC). This allows the initiation of the specific immune response
- The cell debris from the digested bacteria is exocytosed from the macrophage
What types of white blood cells carry out phagocytosis?
Neutrophils and macrophages
How does a macrophage become an APC?
- When a macrophage has digested a pathogen, it combines antigens from the pathogen surface membrane with special glycoproteins in the cytoplasm called the major histocompatibility complex (MHC)
- The MHC moves these pathogens to the macrophage’s surface membrane becoming an APC
- These antigens now stimukate other cells involved in the specific immune system response
What chemicals are involved in phagocytosis?
Cytokines:
- Cytokines act as cell-signalling molecules, informing other phagocytes that the body is under attack and stimulating them to move to the site of infection or inflammation
- Cytokines can also
increase body temperature and stimulate the specific immune system
Opsonins:
- Opsonins are chemicals that bind to pathogens and ‘tag’ them so they can be more easily recognised by phagocytes
- Phagocytes have
receptors on their cell membranes that bind to common opsonins,
and the phagocyte then engulfs the pathogen
- There are a number of
different opsonins, but antibodies such as immunoglobulin G (IgG)
and immunoglobulin M (IgM) have the strongest effect
Draw the blood clotting cascade.
Answer on revision card
