Immunology

Flowchart nodes

• Immunology

• KA 5

• KA 6

• KA 7 

• KA 8 

• Non specific body defences

• Pathogens are bacteria, viruses and other organisms that cause disease 

• The human body has the capacity to protect itself against pathogens, toxins and cancer cells through the immune system 

• Immunity is the ability of the body to resist infection by a pathogen or destroy the organism if it succeeds in invading and infecting the body

• An example of the first line of defence is for the skin to act as a physical barrier to pathogens.

• An example of the second line of defence is cellular response, phagocytosis. 

• Third line defence is the response of T lymphocytes from the Thymus Gland. Also the production of antibodies by B lymphocytes in the bone marrow 

• The surface of the skin is composed of tightly packed epithelial cells which offer physical protection from pathogens

• Mucus membranes that line the digestive and respiratory tracts are also composed of epithelial cells that form a physical barrier

• Secretions from the skin provide chemical defence. Like tears, sweat glands, lining of the stomach and saliva

• When the body suffers a physical injury such as a cut with/without invasion of microbes, it responds by a localised defence mechanism called an inflammatory response at the effected site. 

• Mast cells & histamine 

• Mast cells are produced from the same stem cells as white blood cells. They are present in connective tissue throughout the body and they release histamine

• Histamine is a chemical that causes blood vessels to vasodilate and capillaries become more permeable. 

• After injury, mast cells release large quantities of histamine resulting in blood vessels in the injured area undergoing vasodilation and increased capillary permeability

• This is beneficial because it results in an increased accumulation of phagocytes to the affected are and rapid delivery of blood clotting factors to the affected area

• Phagocytosis

• 1. Phagocytes recognise surface antigen molecules present on a pathogen and move towards it. 

• 2. Phagocytes engulf the pathogen by in-folding the membrane creating a vacuole

• 3. Lysosomes, which contain digestive enzymes to digest the 'foreign' pathogen

• 4. The breakdown products are absorbed by the phagocyte

• 5. Phagocytes release cytokines, cytokines attract more phagocytes to the affected area.

• Lymphocytes are white blood cells that carry out a specific immune response and are produced by stem cells

• There are 2 types of lymphocytes. T & B lymphocytes

• T lymphocytes 

• B lymphocytes produce antibodies against antigens. They are Y-shaped. Antibodies inactivate the pathogens which are later destroyed via phagocytosis. 

• An allergic reaction occurs when B lymphocytes act on an antigen that is harmless to the body, such as pollen. 

• These recognise antigens on the pathogens membrane resulting in apoptosis, cell death. The remains are destroyed by phagocytosis

• Failure of regulations in the immune system results in T lymphocytes acting on self-antigens, causing auto-immune diseases.

• Cloned lymphocytes produced in response antigens survive long term, as memory cells. So if the body has a second exposure, the memory cells will recognise the antigens, resulting in the individual not showing symptoms. 

• The first exposure is known as the primary response, without any cloned lymphocytes resulting in a more serious illness. The secondary response is the memory cells preventing symptoms.

• HIV, this is when T lymphocytes are attacked and destroyed, this then leads to AIDS. The immune system starts to shut down gradually.

• There are 4 types of immunisation.

• 1. Passive Natural: Immediate protection, short term, eg. antibodies from placenta. 2. Active Natural: Develop after lag time, long lasting, includes memory cells, eg. natural exposure to chicken pox. 3. Passive Artificial: Immediate protection, short term, needs medical treatment, eg. tetanus.  4. Active Artificial: Develop after lag time, long lasting, needs medical treatment, eg. whooping cough & MMR.

• Immunity is developed through vaccines. There are 4 ways in which the antigens are exposed to the body. 1. Inactivated pathogen toxin: Tetanus & Diphtheria  2. Dead pathogen: Hepatitis A  3. Parts of pathogen: Hepatitis B & HPV 4. Weakened pathogen: MMR

• Adjuvants are added to vaccines to make them more effective, resulting in increased immunity 

• Herd immunity is protecting and immunising those who aren't protected. This is important because if a large percentage are protected, the spread is reduced.

• The herd immunity threshold is the point in which a minority of a population is unimmunised in order for the pathogens to be resisted. Mass vaccination programmes are held to increase Herd Immunity.

• Antigenic variation is when the antigens of a pathogen  changes such as the flu. It is recommended that individuals who are vulnerable are immunised annually.

• Clinical trials are held to ensure that a vaccine is effective

• Double blind, randomisation and placebo control are types of clinical trials.

• Double blind: Doctors/individuals don't know who is getting what Randomisation: Health info is hidden to prevent bias Placebo Control: Person is given this to see if psychological effects results.

• A computer is used to reduce experimental error, ensuring the trials are fair.