Defence Mechanisms Flashcards
1
Q
what is an infection?
A
- an interaction between the pathogen and the body’s defence mechanisms which overwhelm the defences and the individual dies
- unless the individuals defence mechanism overwhelms the pathogen and the individual recovers from the disease
2
Q
what is immunity?
A
- after the body has overwhelmed the pathogen it is better prepared for a second infection from the same pathogen and can kill it before it can cause harm
- the intermediates that affect peoples ability to become immune depend on the individuals state of health so the young, the old and the sick are at greater risk than health adults
3
Q
what are the body’s defence mechanisms?
A
- skin acts as a barrier to stop pathogens and phagocytosis entering the body
- white blood cells called lymphocytes
4
Q
which immune responses involve lymphocytes?
A
- cell mediate immunity involving T lymphocytes
- humoral immunity involving B lymphocytes
5
Q
why is it important that your body recognises self cells?
A
-if lymphocytes couldn’t distinguish between the body’s own cells and molecules that are foreign the lymphocytes would destroy the organisms own tissues
6
Q
how does your body recognise its own cells?
A
- each type of cell has specific molecules on its surface that identify it
- these molecules can be a variety of types but the proteins have enormous variety and a highly specific tertiary structure
- it is this specific 3D tertiary structure that distinguishes one cell from another
- its the variety of specific 3D structure that distinguishes one cell from another
7
Q
what do proteins allow the immune system to identify?
A
- pathogens like HIV
- non self material like cells from other species
- toxins
- abnormal body cells like cancer cells
8
Q
How do lymphocytes recognise own cells?
A
- there are around 10 million different lymphocytes present at any time each is capable of recognising a different chemical shape
- in the fetus these lymphocytes are constantly colliding with other cells
- infections in the fetus is rare because it is protected from the outside world by the mother and the placenta
- lymphocytes will therefore collide almost exclusively with the body’s own self material
- some of the lymphocytes will have receptors that exactly fit those of the body’s own cells these lymphocytes either die or are suppressed
- the only remaining lymphocytes are are those that might fit foreign material and therefore only respond to foreign material
- in adults lymphocytes produced in the bone marrow initially only encounters self antigens
- any lymphocytes that show an immune response to these self antigens undergo programmed cell death before they can differentiate into mature lymphocytes
- no clines of these anti self lymphocytes will appear in the blood leaving those that might respond to non self antigens
9
Q
how is lymphocytes ability to recognise own cells a disadvantage?
A
- for humans that have had tissue or organ transplants the immune system recognises these non self cells even though they are from individuals of the same species
- it attempts to destroy the transplant
10
Q
how do we limit the effect of tissue rejection?
A
- donor tissues for transplant are normally matched as closely as possible to those of the recipient
- the best matches often come relatives that are genetically close
- immunosuppressant drugs are often given to reduce the level of the immune response that still occurs
11
Q
what do lymphocytes do?
A
- all 10 million types of lymphocytes exist in the body all the time meaning the body has few of each type
- this means there is a high probability that if a pathogen enters the body one of the lymphocytes will have be complementary to the pathogens on the protein however the complementary lymphocyte is few so is stimulated to divide which means it can take time to bring the invading pathogens under control
