Describe the origin, maturation and mode of action of phagocytes #
- originate from stem cells in the bone marrow
- stem cells divide by mitosis
- cells differentiate into specialised cells and stored in the bone marrow
- examples are neutrophils/macrophages/monocytes/
- Monocytes leave the bone marrow before being fully functional and attain maturity in the blood stream.
- After 40-60 hours of circulation by a mature monocyte, it settles in the tissue and increases in size slightly, now a macrophage [e.g. the alveolar macrophage in the alveoli].
- On the other hand neutrophils do not leave bone marrow until maturity
- involved in non-specific responses
- Phagocytes/neutrophils/macrophages act between initial infection by bacteria and immune response.
- All three types of phagocytes share the same job, i.e. phagocytosis [killing by engulfing].
Describe two types of phagocyte: #
- Neutrophil
- The most common type of white blood cell (60%)
- Smaller than macrophages
- Travel throughout the body
- They have a multi-lobed nucleus
- Granulocytes – granular cytoplasm
- Granules contain degradative enzymes
- They are very short lived few hours in blood,
- Monocyte
- Comprise 4% of white blood cells
- Larger than neutrophils
- Bean shaped nucleus
- Agranulocytes – no granules in cytoplasm
- When they leave the blood they act as neutrophils or they differentiate into macrophages – larger cells that patrol tissues especially lungs, liver, spleen and lymph nodes
- Can engulf larges particles e.g. malarial parasite (Plasmodium)
- Some are stationary and line blood spaces in organs such as liver (Kupffer cells)
- Cytoplasm contains numerous larger lysosomes
- Long lived – few days in blood, months or even years in tissues
- Can proliferate in tissues
Distinguish between B- and T-lymphocytes in their mode of action in fighting infection, and describe their origin and functions #
- The lymphocytes are the backbone of our immune system
- the T and B lymphocytes are interdependent
- Both of these cells originate in the stem cells of the bone marrow.
- While the B-cells mature in the bone marrow, the T-cells move as precursors to the thymus gland where they mature
Distinguish between phagocytes and lymphocytes #
| Phagocytes | Lymphocytes |
|---|---|
| macrophages and neutrophils | B and T cells |
| involved in non-specific response/engulfing the bacteria/pathogen/antigen | involved in specific response |
| can squeeze through capillary walls | remain in circulatory system and lymphatic system |
Explain the role of memory cells in long-term immunity #
- produced by both T and B lymphocytes/cells
- survive for long periods
- remain in lymphoid system and circulate in blood and in lymph
- constantly checking for return of pathogen with same antigen
- go fewer divisions before differentiating into plasma cells
- Second response called secondary response
- greater than primary response to original infection
- Antigen presenting cells/APCs continue to expose
- antigen to memory cells to maintain memory
Relate the molecular structure of antibodies to their functions #
- An antibody is a molecule synthesized by an animal in response to the presence of foreign substances called antigens
- Each antibody is a globular protein molecule called immunoglobulin.
- Structure consists of four polypeptide chains
- Two heavy chains and two light chains
- The chains are held together by disulphide bridges
- It has a constant and a variable region
- The variable part is specific to each type of antibody produced
- There are different classes of antibodies e.g. IgS, IgM, IgA, IgE and IgD
- Its structure consists of two heavy chains (H-chains) and two light chains (L-chains)
- It has a constant and variable part, the variable acts like a key which specifically fits into a lock
