Immunity (UNIT 1) Flashcards
ANTIGEN
A molecule that is recognised as non self (foreign) by immune system, this triggers an immune response by lymphocytes. Found on the surface of cells. Usually proteins . Triggers production of antibody.
ANTIBODY
A protein produced by lymphocytes in response to the presence of the appropriate antigen.
PATHOGEN
Any micro-organism that causes disease.
How is the immune system initially activated?
When a pathogen invades the body, the antigens on its cell surface are identified as foreign, which activates the cells in the immune system.
Explain Non- specific defence mechanisms.
Do not distinguish between one type of pathogen and another, but respond to all of them in the same way. Act immediately and take two forms: a) a barrier to the entry of pathogens b) Phagocytosis
Explain Specific defence mechanisms
Distinguish between different pathogens. Responses are less rapid but provide long lasting immunity. The responses involve a type of white blood cell called a lymphocyte and again take two forms: a) cell-mediated responses involving T lyphocytes b) humoral response involving B- lymphocytes
PHAGOCYTOSIS
Mechanism by which cells engulf particles to form a vesicle or vacuole.
LYMPHOCYTES
Types of white blood cell responsible for the immune response. They become activated in the presence of antigens. There are two types: B lymphocytes and T lymphocytes. NOT PRODUCED IN RESPONSE TO AN INFECTION< BUT THEY ALREADY EXIST.
How do lymphocytes work?
So many lymphocytes that high chance that, when pathogen enters body, one of these lymphocytes will have a protein on its surface that is complementary to one of the proteins of the pathogen. RECOGNISES PATHOGEN. Few of each type of lymphocytes. When an infection occurs, the one type already present that has the complementary proteins to those of the pathogen is stimulated to build up its numbers to a level where it can be effective in destroying it. TIME LAG BETWEEN EXPOSURE TO THE PATHOGEN AND BODY’S DEFENCES BRINGING IT UNDER CONTROL.
Barriers to entry (3)
-PROTECTIVE COVERING- Skin, physical barrier that most pathogens find hard to penetrate. -EPITHELIA COVERED IN MUCUS- Pathogens stick to mucus, which is then transported away by cilia, up trachea, to be swallowed. -HYDROCHLORIC ACID IN THE STOMACH- Enzymes of pathogens denatured, organisms killed.
What happens during phagocytosis?
Large particles, such as bacteria, are far too big to cross cell- surface membranes by diffusion or active transport. PHAGOCYTES engulf them.
- Chemical products of the pathogen act as attractants, causing phagocytes to move towards the pathogen.
- Phagocytes attach themselves to the surface of the pathogen.
- They engulf the pathogen to form a vesicle, known as a phagosome.
- Lysosomes move towards vesicle and fuse with it.
- Enzymes within the lysosmes break down the pathogen.
- Soluble products from breakdown of pathogen are absorbed into cytoplasm of phagocyte.
How does phagocytosis cause inflamation
Phagocytosis causes inflammstion at the site of infection. Swollen area contains dead pathogens and phagocytes, which are known as pus. Inflammation is result of release of histamine, causes dilation of blood vessels. This, in turn speeds up delivery of phagocytes to site of infection.
B lymphocytes (B cells)
associated with humoral immunity i.e. immunity involving antibodies that are present in body fluids, or ‘humour’. Formed from stem cells found in bone marrow. MATURE IN BONE MARROW.
T lymphocytes (T cells)
associated with cell-mediated immunity i.e. immunity involving body cells. Formed from stem cells found in bone marrow. MATURE IN THYMUS GLAND
What do T-lymphocytes respond to?
T- lymphocytes respond to an organism’s own cells that have been invaded by non-self material. e.g. virus or cancer cell. Also respond to transplanted material, which is genetically different.