Internal DefenceThe Immune System Yr 11 Biology
Internal DefenceAnimals have internal defence systems toprotect them against disease-causing organismsthat enter the body via;•Air•Food•Water•Wounds in the skin
What causes disease?Disease-causing microorganisms include:•Viruses•Bacteria•Fungi•ProtozoaAll of these organisms are collectively known aspathogens.
Self from non-self?Internal defence relies on the animal’s ability torecognise “self” from “non-self”.Possible because:•Organisms are biochemically unique•Cells have specific surface proteins•Identify between members of the same species•The organism “knows” own cells, and identifiesother cells as “foreign”
The invasion - AntigensDuring an invasion, the presence of these“foreign” cells stimulate a defensive response.A substance capable of stimulating an immuneresponse is called an antigen.Foreign macromolecules include proteins, RNA,DNA and some carbohydrates are all antigenic.
The Defence MechanismsThere are 2 types of defence mechanisms:1.Nonspecific defence – provide general protectionagainst pathogens. Prevent entry, rapidly destroycells that penetrate the body.2.Specific defence – tailor-made to combat specificantigens associated with each pathogen. These arecollectively known as the immune response.Includes antibody production (specific proteins thatbind to antigens).
Defence MemorySpecific defence also has an immunologicalmemory – the capacity to respond moreeffectively the 2nd time a foreign moleculeinvades the body.
Nonspecific Defence1st line – outer covering or skin•A mechanical and chemical barrier tomicroorganisms.•Sweat and sebum (fats and oils secreted by theskin).•Contain chemicals that destroy certain types ofbacteria.
2nd line – internal fluids and structures•HCl and enzymes in stomach – destroymicrobes that enter with food•Cilia in respiratory tract – filter pathogens in air•Mucus lining – traps pathogens (which are then“eaten”•Lysozymes – enzymes in tissues, tears and bodyfluids, attack cell walls of some bacteria
3rd line – the damaged cells.•Release cytokines (regulatory proteins), whichregulate/modify activity of cells.•Some (interferons), signal cells to produce proteinsthat inhibit viral replication (makes the virus weak).•Other interferons – enhance the abilities of otherimmune cells (WBC’s)•Interleukins (cytokines released from macrophagesand lymphocytes) and histamine (released fromcertain WBC’s and injured cells), triggerinflammatory responses
The Inflammatory Response• Causes blood vessels to dilate: – Increases blood flow, temperature, redness, the numbers of phagocytic cells to the invasion site• Capillaries become more permeable: – Increases fluid into tissues, edema (swelling) and pain, antibodies move to tissue• Widespread inflammatory response = fever – Thermostat in the hypothalamus is reset via interleukin produced by macrophages
How fever helps• Interferes with microbe growth• Promotes the activity of lymphocytes (T cells) and the production of antibodies• May increase phagocytosisA short term low fever may therefore help speed recovery.
PhagocytesWhite blood cells that “eat” foreign cells•Neutrophils and macrophages•Inflammatory response increases activity ofthese cells to “eat” invaders by: – Increasing blood flow to infected areas – Increased blood carries more WBC’s to area – Causes localised swelling and pain with response