The Human Defence System

What I need to know from this chapter General defence system skin, mucous membrane of the breathing system, reproductive and digestive tracts. Phagocytic white blood cells Specific defence system Antigen antibody response Definition of “induced immunity” Vaccination & immunisation Role of lymphocytes B & T cell types Role of B cells in antibody production, Role of t cells as helpers, killers, suppressors and memory t cells.

General Defence System Non specific Acts against all pathogens Consists of two parts

1st Part of Defence System Skin Mucus clotting Lysozyme Cilia Acid Sebaceous gland Good bacteria 2nd Part of the Defence System Phagocytic white blood cells Inflammation Defence Proteins/complement system

Skin (1st Line defence) Skin – provides a structural barrier to infection Clotting – prevents entry of pathogens Lysozyme – Enzyme found in sweat, tears, saliva - Dissolves cell walls of bacteria Sebaceous glands – chemicals to kill bacteria

Respiratory Tract (1st Line defence) Respiratory tract lined with mucus -Traps pathogens Respiratory tract has cilia - Moves mucus back up into the throat - carries pathogens out

Digestive Tract (1st Line defence) Produces mucus Produces acid in the stomach - kills many bacteria

Reproductive tract (1st Line defence) Beneficial bacteria in vagina produce lactic acid – prevents growth of pathogens

Phagocytic White Blood Cells (2nd Line Defence) Micro organisms that damage cells These cells release chemicals The chemicals attract white blood cells White blood cells engulf pathogens White blood cells that engulf pathogens are called Phagocytes Large phagocytes called Macrophages – found in Spleen, Tonsils, Adenoids Filter out pathogens from lymph system

Phacocytosis -White Blood Cells “Eating” germ Germ White cell

Inflammation (2nd Line Defence) Infected cells release histamine This causes dilation (widening) of blood vessels The wider the vessel the easier white blood cells can get to the area Which causes vessels to become porous General Inflammation causes a fever High temperature stops bacteria reproducing

Defence Protein (2nd Line Defence) Complement system-group of 20 proteins found in blood plasma When activated they destroy viruses and other pathgen’s by creating a hole in the pathogens cell membrane which make them burst.

Specific Defence System (The Immune System) Attacks particular pathogens Produces antibodies which kill pathogens Produces white blood cells

White Blood Cells Leucocytes Lymphocytes attack cells that contain antigens Lymphocytes produce antibodies Monocytes develop into macrophages Macrophages recognise antigens (foreign molecules) Digest the pathogens & antigens are displayed on the outside of the macrophage this stimulates the production of antibodies

Antibodies An antigen are chemicals that are on the surface of a pathogen An antibody produced by lymphocytes in response to an antigen

Antibodies

What antibodies do Prevent viruses and bacteria from entering new host cells Label pathogens to be destroyed by phagocytes Antibodies can inactivate pathogens by making them clump together Can trigger the complement system – This causes pathogen cells to burst

Complement Protein Pathogen Clump

Antigen Antibody Reaction Highly specific Each antigen stimulates the production of one antibody Why we get flu every year Different strain

Problems Can be disabled - AIDs Body produces antibodies against its own tissues Rheumatoid Arthritis Multiple Sclerosis Allergies

Duration of Immunity After infection antibodies remain 1st time an antigen is produced 14 days to produce maximum no. of antibodies Subsequent infection – 5 days

Induced Immunity Is the ability to resist disease caused by specific pathogens by the production of antibodies. 2 Types of immunity 1. Active 2. Passive

Active Immunity Production of your own antibodies in response to antigens. Is longer-lasting Can be induced naturally or artificially Natural Active Immunity Occurs when pathogen enters body in normal way. Artificial Active Immunity Vaccine is a non disease-causing dose of pathogen, which triggers the production of antibodies Pathogens in vaccine’s are killed/treated (No reproducing) Modern vaccines are genetically engineered

Passive Immunity Given antibodies that were formed by other organisms Short term resistance (Few weeks to 6 months) Induced in 2 ways: Natural Passive Immunity Child gets antibodies from mother Either through the placenta or mothers milk Artificial Passive Immunity Given an injection with antibodies produced by other organism. i.e. Anti-tetanus injection (from horses)

Advanced Study of Lymphocytes 2 Types (mature in different places) B-lymphocytes (B-cells) –Bone Marrow T-lymphocytes (T-cells) – Thymus Gland

B-Cells When matured move from bone marrow to lymphatic tissue –Esp. Spleen and Lymph nodes There are millions Each adapted to recognise 1 specific antigen Produces only 1 type of antibody

B-Cells Divides & produces more B-cells (Plasma cells) on contact with antigen Plasma cells -short lived, produce 2000 AB a second Anti-bodies AB inactivate antigen by attaching to them Disposed 1. phagocytes 2. Complement system (cells burst)

B-Cells Some B-cells remain alive = memory B-cells Secondary response is more effective Produces antibodies to small amounts of antigen Much faster response Greater numbers of antibodies Active in controlling bacterial infections

T-Cells Activated when they move from bone marrow to Thymus Thymus is most active in weeks before & after birth T-cells DON’T produce antibodies 4 types 1. Helper T-cells 3. Suppressor T-cells 2. Killer T-cells 4. Memory T-cells

Helper T-cells Recognise Antigens on surface of other WBC Enlarge, multiply and form a group Secretes a range of chemicals- Interferons This stimulates the production of B-cells HIV infects these helper T-cells & Killer T-cells

Killer T-Cells Attack & destroy abnormal body cells Virus infected or cancer cells (have antigens) Killer cells are triggered by helper t-cells They release protein called Perforin Forms pores in membrane of target cell This allows water to flow in, target cells swells and bursts. Process is called Lysis Killer T-cells said to be Cytotoxic

Suppressor T-Cells Stimulated to grow by specific antigens Grow slowly Activated after antigen has been destroyed They inhibit B-cells, Helper T-cells and killer T-cells This controls the immune response

Memory T-Cells Can survive a long time –life Some stimulate memory B-cells to produce antibodies later in life May trigger Killer T-cells Responsible for life long immunity

THE IMMUNE RESPONSE