immunity
- Created by: Han2812
- Created on: 08-01-14 18:34
Defence Mechanisms
Defence mechanisms are used to protect us from harful pathogens. There are 2 main types:
NON-SPECIFIC:
- Do not distinguish between one type of pathogen and another
- Respond to all of them in the same way - ACTING IMMEDIATELY. Two forms:
- A barrier to the entry of the pathogen
- Phagocytosis
SPECIFIC:
- Do distinguish between different pathogens - SPECIFIC
- Response is LESS RAPID but LONGER LASTING
- LYMPHOCYTES - take 2 forms:
- Cell-mediated response --> T LYMPHOCYTES
- Humoral responses --> B LYMPHOCYTES
There are about 10 million different types of lyphocytes in the body with receptors specific to different pathogens. So when one with that receptor comes along a pathogen with that specific antigen, they have to divide which is why there is a time gap
Phagocytosis
T Cells
T cells are matured in the thymus gland are associated with cell-mediated immunity involving body cells
They respond to an organisms own cells that have been invaded by non-self materia eg. virus or cancer
Process:
- Pathogens invade body cells or are taken up by phagocytes
- Phagocyte puts antigens from pathogen on its cell-membrane surface
- Receptors on some T helper cells fit exactly these antigens
- This activates other T cells to divide rapidly by mitosis and form a clone
- These cloned T cells develop into:
- Memory cells - enable rapid response to future infections by the same pathogen
- Stimulates B cells to divide
- Stimulates phagocytosis in phagocytes
- Killer cells - kills infected cells
How T Cells kill Infected Cells
T cells kill infected cells such as CANCER. They are good at destroying viruses as they live inside cells, so they can reproduce
They do this by:
- They produce a protein that makes holes in the cell-surface membrane
- This makes the cell freely permeable to all substances and it dies
This shows the importance of the cell-surface membranes that cells have to survive
B Cells
B Cells are matured in the bone marrow - involved in HUMORAL IMMUNITY - antibodies in body fluids. They are used to help fight off infections with T cells
Process:
1. Surface antigens of the invading pathogen are taken up by B cells
2. B cells process the antigens and present them on their cell-surface membrane
3. T helper cells activate them by attaching to the processed antigens
4. The B cells then divide by mitosis to give a clone of a PLASMA cell
5. The cloned plasma cell PRODUCE ANTIBODIES --> fit EXACTLY to the antigens on the pathogens cell-surface membrane
6. The antibodies attach to the antigens on the pathogen, destroying them. PRIMARY RESPONSE SYSTEM
7. Some B cells develop into MEMORY CELLS --> respond quickly in future infections of same pathogen --> SECONDARY RESPONSE SYSTEM
Antibodies
Antibodies are proteins synthesised by B cells
Polyclonal Antibodies: Antibodies that are produced in our body
Monoclonal Antibodies: Antibodies that are produced outside our bodies
Vaccinations
There are two types of immunity
1. PASSIVE - Introduction of antibodies into individuals from an OUTSIDE SOURCE. These are not being produced by the individual themselves, not replaced when being broken down --> Immunity is SHORT
2. ACTIVE - Stimulating the production of antibodies by the individual's own immune system. Generally LONG LASTING
Vaccinations are the introduction of a substance into your body with the intention of stimulating active ummunity against a particular disease for individuals and whole populations so ACTIVE IMMUNITY
Vaccinations - Successful and Not
To have a sucessful vaccination program depends on a number of factors:
- Must be economically avaliable in enough quantities to immunise all the vulnerable population
- Only a few side effects. Unpleasant side effects may make populations not get immunised
- Must be ways of producing, storing and transporting the vaccine - hyginic conditions ect
- Must be ways of advertising the vaccine properly at the right time - staff training ect
- HERD IMMUNITY - all vunerable people if possible vacinnated at one time --> so at a certain time, no-one in a population has the disease and transmittion of pathogen is interrupted
Sometimes, vaccines don't always eliminate a disease. This is because:
- They fail to immunise some people - eg. have weak/defective immune system. Some people just dont want to have them done - scared, religious, ethical or medical reasons
- Individuals may develop the disease after getting the vaccine - immunity levels aren't high enough to prevent it
- Vaccine is ineffective as pathogen has mutated as antigens aren't recognised by the immune system - ANTIGENTIC VARIABILITY - happens alot with influenza virus
- May be many varieties of one type of pathogen - near immpossible to vaccinate against all of them + some hide from bodies immune system
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