Immunity Flashcards
Describe and explain the two different types of defence mechanisms if pathogens enter the body
1) Non-specific- These defence mechanisms are not specific to individual types of pathogens. E.g. phagocytosis
2) Specific immune response- This type of response does distinguish between individual pathogens and the response is tailored to the pathogen involved. Specific immune responses take LONGER to work but tend to provide LONG TERM IMMUNITY. They involve lymphocytes, a specialised type of white blood cell.
Describe and explain the barriers preventing pathogen entry in humans
1) Skin - provides a tough physical barrier that most pathogens cannot penetrate.
2) The enzyme lysozyme- contained in tears, saliva and sweat- anti-bacterial as it is able to break down (hydrolyse) bacterial cell walls. Tears can also wash away debris and pathogens from the front of the eye
3) Epithelial lining covered in mucus (e.g. respiratory tract)- the mucus traps pathogens and prevents them penetrating the underlying membranes. Cilia sweep the mucus and trapped pathogens back up the trachea
4) Hydrochloric acid in the stomach- kills most pathogens that are in the food we eat or liquids we drink. Provides a very low pH that denatures the enzymes of the pathogens.
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If pathogens enter the body what is the body’s next defence mechanism?
-Phagocytosis
-Non-specific but has the advantage of being rapid
-Carried out by a number of types of white blood cell, collectively known as phagocytes
Describe the inflammatory response and signs of inflammation
-The capillaries in the affected area become leaky, allowing plasma to seep into the surrounding areas.
-Inflamed parts of the body become swollen with phagocytes, dead pathogens and cell debris, collectively known as pus.
-Inflamed areas appear red due to increased blood flow to that area and also become hot as raised temperature helps reduce infection by denaturing the enzymes in the pathogen
Describe the process of phagocytosis
-Phagocytes including polymorphs and macrophages squeeze through the capillary walls and engulf the pathogenic bacteria and surrounding cell debris at the site of infection.
1) Phagocyte moves towards the pathogen, attracted by the chemicals it produces.
2) As it does so the phagocyte membrane invaginates to begin to enclose the pathogen.
3) As the pathogen is engulfed, the invaginated phagocyte membrane forms a vesicle (phagosome) around the pathogen
4) Lysosomes move towards the phagosome and fuse with it
5) Hydrolytic enzymes within the lysosomes are released into the phagosome, onto the pathogen and hydrolyse the pathogen
6) The soluble digested products are absorbed into the cytoplasm of the phagocyte
What are specific immune responses associated with and how are they triggered?
-Specific immune responses are associated with lymphocyte white blood cells
- The responses are triggered by the body being able to recognise “foreign” cells, linked to the concept of self and non-self tissue.
Explain non-self cells
-Foreign (non-self) cells are cells not recognised by the body
-If detected they will produce an immune response.
How do non-self cells produce a specific immune response?
-It is specific molecules/ clusters of molecules that form part of the cell surface membrane that are recognised as foreign
-These molecules are often protein but can be other substances e.g. polysaccharides, glycoprotein and glycolipid, and are collectively referred to as ANTIGENS
-Different pathogens have different antigens- immune response is specific to these antigens
-Lymphocytes have receptors on their cell surface membrane that is complementary in shape to the antigen- antigen and lymphocyte fit together like substrate and enzyme in the LOCK AND KEY model of enzyme action
Define antigens
Antigens are chemicals capable of producing a specific immune response
How do lymphocytes know what cells are self and non self?
-Many million different types of lymphocytes, each having receptors with a complementary shape to a potential antigen
What happens in the foetus to lymphocytes that are complementary in shape with foetal cells?
-In the foetus lymphocytes frequently make contact with other foetal (self) cells.
-Lymphocytes complementary in shape with foetal cells are SWITCHED OFF so by the time the baby is born the functional lymphocytes that remain are those that are not complementary to self cells.
-This prevents an immune response to self cells
Why is the specific immune response relatively slow?
There are millions of different types of lymphocytes but only a few of each type
What are the two types of lymphocyte?
1) B-lymphocytes (B-cells)
2) T-lymphocytes (T-cells)
Describe B-lymphocytes
-Formed from stem cells in the bone marrow
-Mature in bone marrow
-Name of immune response- antibody-mediated immunity
-Produce antibodies which respond to antigens found in body fluids (e.g. blood and tissue fluid). Respond usually to bacterial or viral infection
Describe T-lymphocytes
-Formed from stem cells in the bone marrow
-Mature in the thymus gland (lymph gland in the neck)
-Name of immune response- cell-mediated immunity
-Respond to antigens attached to body cells (antigen presenting cells). Respond usually to body cells affected by viral infection.
