Biology - The Defence System

immunity

resistance to infectious diseases

pathogen

a disease-causing organism

examples of pathogens

influenza - virus

cholera - bacterium

malaria - protist

ringworm - fungus

organisms of the defense system

spleen, thymus gland, tonsils

general defence system

barrier system which stops pathogens from entering the body and cells

first line of defence of general defence system

• sebum - an oil produced by sebaceous glands. it contains chemicals which kill microorganisms + sebum stops the skin from drying out and cracking

• mucus membranes found - produce mucus which traps foreign particles

• cilia - small hair-like structures that push mucus out of the respiratory system

• HCl - hcl in stomach kills bacteria by denaturing their enzymes

• blood clotting - if skin is broken, a blood clot stops the entry of pathogens

• lysozyme - antibacterial enzyme found in sweat, tears and saliva

second line of general defence

• phagocytes and macrophages - WBCs that engulf pathogens

• complement proteins - produced by the liver, they cause abnormal cells to burst

• interferons - chemicals that attck viruses

• inflammation - infected cells produce histamine → blood vessels dilate, blood containing WBCs is carried to the area

• fever - high body temperature will prevent microorganisms reproducing

specific defence system

attacks one particular pathogen only. it works by:

• the production of antibodies

• using white blood cells to attack cells which have been infected by a pathogen

antigens

surface proteins on cells that cause the production of antibodies

antibodies

proteins produced by lymphocytes in response to an antigen. Antibodies destroy pathogens

antigen-antibody reaction

highly specific reaction. Each antigen causes the production of one particular antibody which targets that antigen

how do antibodies destroy pathogens

1. cause them to clump together

2. triggering the complement system

3. preventing pathogens from entering cells

immunisation

the protection against pathogens by vaccination or by injection of antibodies

vaccination

the administration of a non-disease-causing dose of a pathogen or it’s antigen, this causes antibody production

induced immunity

fights infection using antibodies

passive induced immunity

means that antibodies are given to or introduced to the body

e.g. antibodies cross the placenta into the foetus / in breast milk / monoclonal antibodies

active induced immunity

antibodies produced in the person’s body

e.g. catching a cold / vaccination

B Cells

• made in bone marrow

• mature in red bone marrow

• recognise antigens

• produce antibodies

• some remain as memory cells → can last in the body for years. they recognise and remember the antigen/pathogen + cause the production of lots of antibodies rapidly

T Cells

• made in red bone marrow

• mature in thymus gland

• 4 types: helper, killer, memory, suppressor

types of T cells

Helper:

• Recognise antigens. • Stimulate B cell production. • Activate killer T cells.

Killer:

• Recognise antigens. • Cause abnormal cells to burst by producing perforin

Memory:

• Recognise antigens. • Stimulate the production of killer cells. • Stimulate B cell production

Suppressor:

• Stop immune response. • Inhibit B cell production

immunological memory

Memory (B cells and T cells) remain in the body for a long time, up to 20 years.

• If the same infection occurs, they recognise/remember the antigen.

• The memory B cells cause the production of large amounts of the specific antibody quickly.

to explain a given graph: • The first time the virus attacks the body a small number of antibodies are produced after approximately 8 days. • The second time the virus attacks the body, a larger number of antibodies are produced immediately.

antibiotic

An antibiotic is a chemical produced by micro-organisms and it kills/slows the growth of other micro-organisms without harming human tissue

autoimmune disease

when the defence system attacks normal healthy body cells. Multiple sclerosis and coeliac disease are examples of auto immune diseases