chapter 12 p3 Flashcards
Non-specific defences - getting rid of pathogens:
If the pathogens get into the body, the next lines of defence are adaptations to prevent them growing or to destroy them.
Fevers:
Normal body temperature of around 37°C is maintained by the hypothalamus in your brain. When a pathogen invades your body, cytokines stimulate your hypothalamus to reset the thermostat and your temperature goes up.
This is a useful adaptation because:
This is a useful adaptation because:
- most pathogens reproduce best at or below 37°C. Higher temperatures inhibit pathogen reproduction
- the specific immune system works faster at higher temperatures.
Phagocytosis:
Phagocytes are specialised white cells that engulf and destroy pathogens.
There are two main types of phagocytes - neutrophils and macrophages (Figure 2).
Phagocytes build up at the site of an infection and attack pathogens.
Sometimes you can see pus in a spot, cut or wound.
Pus consists of dead neutrophils and pathogens.
The stages of phagocytosis:
- Pathogens produce chemicals that attract phagocytes.
- Phagocytes recognise non-human proteins on the pathogen.
- This is a response not to a specific type of pathogen, but simply a cell or organism that is non-self.
- The phagocyte engulfs the pathogen and encloses it in a vacuole called a phagosome.
- The phagosome combines with a lysosome to form a phagolysosome
- Enzymes from the lysosome digest and destroy the pathogen.
Neutrophils vs macrophages:
- It usually takes a human neutrophil under 10 minutes to engulf and destroy a bacterium.
- Macrophages take longer but they undergo a more complex process.
- When a macrophage has digested a pathogen, it combines antigens from the pathogen surface membrane with special glycoproteins in the cytoplasm called the major histocompatibility complex (MHC).
- The MHC complex moves these pathogen antigens to the macrophage’s own surface membrane, becoming an antigen-presenting cell (APC).
- These antigens now stimulate other cells involved in the specific immune system response
Counting blood cells:
blood smears are made by spreading a single drop of blood very thinly across a slide.
They are often stained to show up the nuclei of the lymphocytes, making them easier to identify.
Identifying the numbers of different types of lymphocytes in a blood smear indicates if a non-specific or specific immune response is taking place.
Helpful chemicals:
- Phagocytes that have engulfed a pathogen produce chemicals called cytokines.
- Cytokines act as cell-signalling molecules, informing other phagocytes that the body is under attack and stimulating them to move to the site of infection or inflammation.
- Cytokines can also increase body temperature and stimulate the specific immune system.
- Opsonins are chemicals that bind to pathogens and ‘tag’ them so they can be more easily recognised by phagocytes.
- Phagocytes have receptors on their cell membranes that bind to common opsonins, and the phagocyte then engulfs the pathogen.
- There are a number of different opsonins, but antibodies such as immunoglobulin G (IgG) and immunoglobulin M (IgM) have the strongest effect.
Chapter 12.6 - The specific immune system
All cells have molecules called antigens on their surfaces.
The body recognises the difference between self antigens on your own cells and non-self antigens on the cells of pathogens.
Some toxins also act as antigens. Antigens trigger an immune response, which involves the production of polypeptides called antibodies.
The specific immune system (also known as active or acquired immunity) is slower than the non-specific responses - it can take up to 14 days to respond effectively to a pathogen invasion.
However, the immune memory cells mean it reacts very quickly to a second invasion by the same pathogen.
Antibodies:
Antibodies are Y-shaped glycoproteins called immunoglobulins, which bind to a specific antigen on the pathogen or toxin that has triggered the immune response.
There are millions of different antibodies, and there is a specific antibody for each antigen.
Structure:
- Antibodies are made up of two identical long polypeptide chains called the heavy chains and two much shorter identical chains called the light chains
- The chains are held together by disulfide bridges and there are also disulfide bridges within the polypeptide chains holding them in shape.
- Antibodies bind to antigens with a protein-based lock-and-key’ mechanism similar to the complementarity between the active site of an enzyme and its substrate.
- The binding site is an area of 110 amino acids on both the heavy and the light chains, known as the variable region.
- It is a different shape on each antibody and gives the antibody its specificity.
- The rest of the antibody molecule is always the same, so it is called the constant region.
- When an antibody binds to an antigen it forms an antigen-antibody complex.
- The hinge region of the antibody provides the molecule with flexibility, allowing it to bind two separate antigens, one at each of its antigen-binding sites.
How antibodies defend the body:
The antibody of the antigen-antibody complex acts as an opsonin so the complex is easily engulfed and digested by phagocytes.
Most pathogens can no longer effectively invade the host cells once they are part of an antigen-antibody complex.
Antibodies act as agglutinins causing pathogens carrying antigen-antibody complexes to clump together - This helps prevent them spreading through the body and makes it easier for phagocytes to engulf a number of pathogens at the same time.
Antibodies can act as anti-toxins, binding to the toxins produced by pathogens and making them harmless.
Lymphocytes and the immune response:
The specific immune system is based on white blood cells called lymphocytes. B lymphocytes mature in the Bone marrow, while T lymphocytes mature in the Thymus gland.
