Defence mechanisms, phagocytosis

What are the two types of defence mechanism?

What are the two types of defense mechanisms including white blood cells?

• cell mediated responses involving T lymphocytes

• humoral responses involving B lymphocytes

What can the immune system identify?

Each type of cell has specific molecules on its surface that identify it. These molecules include proteins and enable the immune system to identify:

• pathogens

• non-self materials e.g. cells from other organisms of the same species

• toxins

• abnormal body cells e.g. cancer cells

Why is there a time lag between exposure to the pathogen and the body defending itself?

• lots of types of lymphocyte so not many of each

• when infection occurs, lymphocyte with complementory proteins is stimulated to divide to build up numbers

• takes time for number of lymphocytes to be enough to destroy infection

How do lymphocytes recognise self body cells?

• in fetus, lymphocytes constantly colliding with other body cells pretty exclusively

• some lymphocytes will have receptors that fit the body’s own cells

• these lymphocytes either die or are suppressed

• only remaining lymphocytes are those that might fit foreign material

• in adults, lymphocytes in bone marrow initially only encounter self-antigens

• any lymphocytes showing an immune response to self-antigens undergo cell death (apoptosis)

• only lymphocytes left will respond to non-self antigens

What is the definition of an antigen?

a toxin or other foreign substance which indices an immune response in the body, especially the production of antibodies

What is phagocytosis?

The process in which bacteria is engulfed by white blood cells to defend against pathogens entering the body

What is the process of phagosytosis

• pathogen moves towards phagocyte down chemical concentration gradient

• phagocyte receptors on cell-surface membrane attach to chemicals on the surface of the pathogen

• pathogen is engulfed into a phagosome

• lysosomes move towards phagosome and fuse with it

• lysosomes release hydrolytic enzymes lysozymes which destroy bacteria by hydrolysis