Communicable Diseases, Disease Prevention and the Immune system Flashcards
what is a pathogen?
any micro-organism which cause disease
what are primary defences?
primary defences are mechanisms which prevent the entry of pathogenic organisms and are always non specific
what are secondary defences?
secondary defences evolved to tackle the pathogens that have entered the body and can be specific or non specific
what are non specific responses?
non- specific responses are often general and more immediate.
they involve physical barriers (such as the skin preventing pathogen entry) and some cellular processes such as phagocytosis.
(skin, blood clotting, mucous membranes, expulsive reflexes, tears, inflammation, phagocytosis)
what are specific responses?
specific responses are less rapid ad longer lasting.
these responses involve a white blood cell called a lymphocyte and take 2 forms:
- T lymphocytes (T cell) are involved in the cell mediated response
-B lymphocytes (B cell) are involved in the humoral response
what is keratinisation?
the process in which the cytoplasm of the keratinocytes is replaced by the protein keratin
how does the skin act as the main non- specific primary defence?
- it’s made mostly of cells called keratinocytes
- these cells are produced by mitosis at the base of the epidermis and then migrate to the surface of the skin, drying out as they move upwards
- over 30 days keratinocytes migrate ou to the top of the skin
- keratinisation takes place (the process in which the cytoplasm of the keratinocytes is replaced by the protein keratin)
- these cells eventually die by the time they reach the surface of the skin where they act as barrier to the pathogen
- eventually the dead cells slough off and are replaced
- Also lots of harmless microbes called skin flora also live on the skin preventing pathogenic microbes from colonising on the sin by competing with them for nutrients
how does blood clotting and wound repair act as a non specific primary defence?
- when a blood clot dries, it forms a temp seal called a scab allowing the skin to repair
- the scab shrinks as it dries bringing the edges of the cut together
- to trigger blood clotting, platelets and damages tissues release clotting factors which activate an enzyme cascade
- to repair the skin, fibrous collagen is deposited under the scab, and the stem cells divide by mitosis in the epidermis to produce new cells
- the new cells then migrate to the edges of the cut before differentiating to form new cells
- these new cells then migrate to the edges of the cut before differentiating to form new skin cells
- they’re supplied with oxygen and nutrients by the growth of new blood vessels
how does the mucus membrane act as a non specific primary defence?
- exchange surfaces where oxygen and nutrients enter the blood are thinner and more exposed to pathogens
- these areas are protected by mucus membrane, specialised epithelial tissue covered by mucus
- in the airways, goblet cells and glands secrete mucus, which traps pathogens
- the epithelium lining the airways contains ciliated cells from which tiny hair-like structures called cilia protrude
- the cilia waft in a coordinated fashion to move the mucus (containing trapped pathogens) to the top of the trachea
- the mucus is then swallowed and moves down the oesophagus before entering the stomach
- the low pH of stomach acid kills the pathogens as their enzymes become denatured
how do expulsive reflexes act as a non specific primary defence?
- some pathogens can release toxins
- areas which are at risk of infection are very sensitive to pathogens and their toxins
- when these areas are irritated, they respond with a expulsive reflex (coughing, sneezing, vomiting)
- this reflex causes are or fluid to be suddenly forced out of the body which carries the pathogen put with it
what are some non specific chemical defences and how do the work?
- saliva, tears nasal secretion
- these contain and enzyme called a lysozyme
- lysozyme kills bacteria by breaking down the bacterial cell wall
- the lysis of the pathogen prevents it from entering nose, eyes and mouth so it cannot cause disease
what is inflammation?
when a pathogen infects a tissue- it can cause a tissue to turn red and swell.
-this helps destroy invading pathogens
how does inflammation act as a non specific primary defence?
1-the pathogen is detected in the tissues by mast cells (a specialised type of phagocytic cell
2-pathogen detection triggers mast cells to release the cell- signalling chemical histamine. Histamine causes vasodilation, thus making the capillary walls in tissues more permeable to white blood cells
3-more white blood cells can therefore move out of the capillaries into the tissue fluid and reach the site of the infection
4-vasodilation causes more tissue fluid to be produces, which leads to swelling (oedema)
5-the excess tissue fluid is then drained into the lymphatic system where other immune cells are stored. these immune cells can then attack the pathogens present in the tissue fluid
what is phagocytosis?
this is where a specific type of white blood cell (called a phagocyte) engulfs and digests pathogens to stop them causing damage.
-some phagocytes can travel in the blood and move out into the tissues when they are needed
what is phagocytosis used for?
-phagocytosis is also used to remove dead, damaged or abnormal
