What is the immune system?
The immune system is a part of the lymphatic system which protects the body from disease causing organisms (pathogens). There are many types of pathogens, the most common being viruses and bacteria.
The immune system protects the body from invading pathogens through both (a) non-specific mechanism and (b) specific resistance (immunity).
The immune system is prevents the body from becoming ill and dying from an infection from a pathogen, so has a very important role in the body’s defences.
Important immune system facts
- The immune system is the body’s main line of defence against invading bacteria and viruses
- The immune system provides many defence mechanisms
- The thymus gland is important as it matures the T cells which help to destroy the pathogens
- The B cells, which provide immunity are matured in the bone marrow
Why the immune system is important
The immune system is responsible for defending the body from invading pathogens which take any opportunity to infect the body – without the immune system, the body would not survive long.
The immune system consists of the following defence mechanisms:
1. Non-specific defence mechanisms
These are normally the first line of defence in preventing the pathogens from entering the body (or expelling them when they first enters) are
- Barriers – skin, mucous, hair and sebum
- Expulsion – vomiting, diarrhoea, lacrimation (tears), sneezing, urination, defacation
- Chemical – saliva, skin pH, stomach acid, sweat
- Metabolic – fever, inflammation, phagocytosis (where the invading pathogen is englufed by the cell and destroyed), interferon (secreted by natural killer cells – NK cells), complement cascade
2. Specific resistance (immune response)
This type of defence includes the T lymphocytes (T cells) and the B lymphocytes (B cells), which are all white blood cells. Many pathogens (invading viruses and bacteria) provoke both types of immune responses from both the T cells and the B cells.
The T cells and the B cells provide a specific response to a particular pathogen in a particular way:
- T cells – cytotoxic T cells target infected cells by secreting chemicals that destoy the cell – by either create holes in it or by destroying the cell’s DNA
- B cells – clone into specialised plasma cells that produce antibodies in response to an infection