2.4 Defence mechanisms Flashcards
What is an infection?
- An interaction between the pathogen and the body’s various defence mechanisms.
- Sometimes the pathogen overwhelms the defences and the individual dies
- Sometimes the body’s defence mechanisms overwhelm the pathogen and the individual recovers from the disease
What is immunity?
Having overwhelmed the pathogen, the body’s defences seem to be better prepared for a second infection from the same pathogen and can kill it before it can cause any harm
What is the immune system?
A system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumour cells
How can pathogens enter the body?
- The eye
- The respiratory system
- The skin
- The stomach
- The urinary tract and vagina
- Saliva
How can pathogens enter the body through the eye?
- Tears and the conjunctiva and antibacterial enzymes
How can pathogens enter the body through the respiratory system?
Muscles and cilia
How can pathogens enter the body through the skin?
Sebum and sweat
How can pathogens enter the body through the stomach?
Hydrochloric acid
How can pathogens enter the body through the saliva?
Antibacterial enzymes
What are pathogens?
Microorganisms that cause disease
What impact do parasites have?
They have a close relationship with their host, and have a negative impact on the host
What conditions are needed in the stomach to kill pathogens?
Acidic conditions in the stomach kill pathogens
What is toxic to pathogens?
Antibacterial enzymes in tears and saliva are toxic to pathogens
What is the urinary tract protected by?
The urinary tract is protected by the urine which flushes out microorganisms
What does the vaginal tract contain?
The vaginal tract contains acid
What is the respiratory system protected by?
The respiratory system is protected by goblet cells and mucus
What are the two types of defence mechanisms?
- Non specific
- Specific
How do you defend the body from invasion by foreign material?
To defend the body from invasion by foreign material, lymphocytes must be able to distinguish the body’s own cells and molecules (self) from those that are foreign (non-self).
What happens if the body could not defend itself from invasion by foreign material?
If they could not do this, the lymphocytes would destroy the organisms own tissues
What do each type of cells have on its surface?
Each type of cell, self or non-self, has specific molecules on its surface that identify it
Why are proteins the most important of the specific molecules that identify it?
Because proteins have enormous variety and a high specific tertiary structure. It is this variety of specific 3D structure that distinguishes one cell from another
What do the protein molecules allow the immune system to identify?
- Pathogens, for example the human immunodeficiency virus
- Non-self material such as cells from other organisms of the same species
- Toxins including those produced by certain pathogens like the bacterium that causes cholera
- Abnormal body cells such as cancer cells
What are the implications for humans of protein molecules allowing the immune system to identify things?
- It has implications for humans who have had tissue or organ transplants
- The immune system recognises these as non-self even though they have come from individuals of the same species
- Therefore attempts to destroy the transplant
How can you minimise the effect of tissue rejection?
- Donor tissues for transplant are normally matched as closely as possible to those of the recipient
- The best matches often come from relatives that are genetically close
- In addition, immunosuppressant drugs are often administered to reduce the level of the immune response that still occurs
What are the types of non-specific defence mechanisms?
- Physical barrier e.g skin
- Phagocytosis
What is a non specific defence mechanism?
The response is immediate and the same for all pathogens
What is a specific defence mechanim?
The response is slower and specific to each pathogen
What are the types of specific defence mechanisms?
- cell-mediated response e.g T lymphocytes
- Humoral Response e.g B lymphocytes
How do lymphocytes recognise cells belonging to the body?
- There are around 10 million different lymphocytes present at any time, each capable of recognising a different chemical shape
- In the foetus, these lymphocytes are constantly colliding with other cells
- Infection in the foetus is rare because it is protected from the outside world by the mother and, in particular, the placenta
- Lymphocytes will therefore collide almost exclusively with the body’s own material (self)
- 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 those that might fit foreign material, and therefore only respond to foreign material
- In adults, lymphocytes produced in the bone marrow initially only encounter 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 clones of these anti self lymphocytes will appear in the blood, leaving only those that might respond to non-self antigens
What 2 forms do lymphocytes take?
- Cell mediated responses involving T lymphocytes
- Humoral responses involving B lymphocytes
