Immunity Flashcards
What is immunity?
Immunity is the protection against disease by the body’s internal defence or immune system.
Give 4 examples of external defenses against infection by the body.
- Epithelia covering the airways serve as a barrier to the entry of pathogens
- Mucus produced in the respiratory tract trap pathogens that have made their way there
- Blood clotting prevents pathogens from entering the body through open wounds
- Hydrochloric acid in the stomach kills pathogens that have been ingested
What is an antigen?
The large molecules on the surface of pathogen (proteins, glycoproteins, lipids, glycolipids, polysaccharides and toxins and waste materials) that are foreign to the body and stimulate an immune response
Describe what is meant by ‘self’ and ‘nonself’
This refers to the recognition of antigens of cells that are foreign to the body: nonself; in relation to the cell surface antigens unique to an organism: self. This explains how/why pathogens stimulate immune responses.
What is an antibody?
A glycoprotein (immunoglobin) produced by lymphocytes in response to the presence of a specific antigen. Different types have shapes complementary to specific types of antigens.
Name the two white blood cells of the immune system you have studied.
Phagocytes - macrophages and neutrophils
Lymphocytes- T-killer and T-helper cells
Mention three characteristics of neutrophils
- They are small cells that make up 60% of all the white blood cells in the body
- They squeeze through the capillaries and into tissues patrolling the body for pathogens
- They are short-lived
Outline the mode of action of neutrophils.
Include the term endocytosis.
- Pathogens and cells under attack release chemicals that attract neutrophils to the site of infection. Additionally, antibodies binded to the surface of the pathogens are a trigger as neutrophils have receptor proteins that recognise them. These response to the chemical stimuli created is called chemotaxis.
- Neutrophils attach to the anitbodies and the cell surface membrane extends to engulf the whole complex in a phagocytic vacuole or phagosome in a process called endocytosis
- Lysosomes fuse with the vacuole and release enzymes called lysozymes into it which breakdown the enzymes
Mention three characteristics of macrophages
- They do not remain in the blood but are found in organs such as the lungs, kidneys, spleen, liver and lymph nodes
- They are formed as monocytes in the bone marrow but develop into macrophages at these organs
- They are long-lived
Outline the mode of action of macrophages
They cut up the pathogens through a structure called the major histocompatibility complex and expose their antigens for lymphocytes to recognise easier.
What are the two different lymphocytes and how do they differ?
B and T lymphocytes. Both are made in the bone marrow before birth-
* but B lymphocytes remain there and mature before being distrubuted throughout the body concentrating in the spleen and in the lymph nodes
* T lymphocytes leave the bone marrow and are collected in the thymus where they develop.
Discuss the cycle of B-lymphocytes
They mature to be able to produce one type of antibody as their genes eventually code for different types of antibodies.
The cells divide to make a small number of identical cells called clones.
At maturity each type of B cell is able to produce one type of antibody, and at this stage the part of the antibody molecules are used to make glycoprotein receptors which remain on the cell surface membrane.
What is clonal selection and the clonal expansion stage?
Clonal selection is the process whereby B cells with antibodies specific to one kind of antigen are replicated through mitosis. The clonal expansion stage is where many of these cells are produced over a period of weeks.
What happens ot the large number of B-lymphocytes produced by clonal selection?
Some of them become plasma cells that remain in the blood for a short while and produce antibodies. And others develop into longer-lasting memory cells.
Differentiate between the primary and secondary immune response.
The primary immune response is the response to a newly encountered antigen and the secondary response is the subsequent responses to familiar or previously encountered antigens.
With primary responses B-lymphocytes are now undergoing the production of antibodies to fight the pathogen, but secondary responses find that memory cells recognise the antigen again and divide and develop to produce plasma cells and more memory cells.
Primary responses are slower as there are only a few number of B-cells specific to that antigen.
