The immune system
- Created by: jasminntan
- Created on: 08-06-16 12:12
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The immune system has non-specific and specificcresponses to pathogens. Auto-immune diseases are the result of failures in the system to distinguish between self and non-self.
1. State that phagocytes (macrophages and neutrophils) have their origin in bone marrow and describe their mode of action
- Phagocytes are produced in the bone marrow
- They are stored there before being distributed throughout the entire body in the blood
- They are scavengers, removing any dead cells as well as invasive microorganisms
- Neutrophiles
- They are agranulocyted phagocytes and they travel throughout the body by squeezing through the walls of blood capillaries to 'patrol' the tissues
- During an infection, neutrophils are released in large numbers
- Histamine is released by cells under attack and these, with any chemicals released by the pathogens themselves, attract passing neutrophils
- This movement towards a chemical stimulus is called chemotaxis
- The neutrophils move towards the pathogens and the antibodies which cover the clustered pathogens further stimulates the neutrophils to attack the pathogens
- When the neutrophil attaches to the pathogen, the neutrophil's cell surface membrane engulfs the pathogen and traps it within a phagocytic vacuole in a process called endocytosis
- Digestive enzymes are secreted into the vacuole so the pathogen is destroyed
- After neutrophils kill and digest some pathogens, they die so they have a short life
- Macrophages
- They are granulated phagocytes and are larger than neutrophils
- They tend to be found in organs such as the kidney and lymph nodes rather than remaining in the blood
- Macrophages travel in the blood as monocytes after they are produced in the bone marrow
- They only develop into macrophages once they settle into the organs
- They are long-lived cells and play a crucial role in initiating the immune responses
- They do not completely destroy pathogens, but cut them up to display the antigens that can be recognised by the lymphocytes
2. Describe the modes of action of B-lymphocytes and T-lymphocytes
- B-lymphocytes (B cells) are in charge of the humoral response
- They remain in the bone marrow until they mature then they move around the body, concentrating in the lymph nodes and the spleen
- When an antigen enters the body for the first time, the small numbers of B cells with receptors complementary to the antigen are stimulated to divide by mitosis in the clonal expansion stage
- Some of these activated B cells become plasma cells and produce antibody molecules very quickly
- Plasma cells secrete antibodies into the blood or lymph and these plasma cells do not live long
- Other B cells become memory cells
- These cells remain circulating in the body for a long time so if the same antigen is reintroduced, memory cells divide rapidly and develop into plasma cells and more memory cells
- T-lynphocytes (T cells) are responsible for the cell mediated response
- The leave the bone marrow and collect at the thymus when they mature
- Mature T cells have specific cell surface receptors called T cell receptors
- T cell receptors have a structure that are similar to that of antibodies and they are each specific to one antigen
- T…
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