6. Defence Against Infectious Disease Flashcards Preview

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Flashcards in 6. Defence Against Infectious Disease Deck (20):

What is a pathogen?

an organism or virus that causes disease


What are the body's primary defence against pathogens? How do they work?

- skin and mucous
- by forming a barrier preventing entry


How does the skin act as a barrier preventing pathogens from entering the body?

- outer layers of skin are tough and form a physical barrier
- sebaceous glands in the skin secrete lactic acid and fatty acids, which make the surface of the skin acidic. this prevents the growth of most pathogenic bacteria


How do mucous membranes act as a barrier preventing pathogens from entering the body? Where are they found? How

- mucous membranes are soft areas of skin that are kept moist with mucus
- Although they do not form a strong physical barrier, many bacteria are killed by lysosome, an enzyme in mucus
- mucous membranes are found in the nose, trachea, vagina and urethra
- in the trachea pathogens get caught in the sticky mucus; cilia then push the mucus and bacteria up and out of the trachea


What other defences, apart from skin and mucus, does the body have?

white blood cells:
- phagocytes
- lymphocytes


How do phagocytes 'kill' pathogens?

- phagocytes ingest pathogens by endocytosis
- pathogens then killed and digested inside the cell by enzymes from lysosomes


Where do phagocytes act?

- in the blood
- can also squeeze out through the walls of blood capillaries and move through tissues to sites of infection. They then ingest the pathogens causing the infection


What do large numbers of phagocytes at an infection form?




What sort of immunity do phagocytes give us? Why?

- non-specific immunity to diseases, because a phagocyte does not distinguish between pathogens - it ingests any pathogen if stimulated to do so


Draw and label a phagocyte ingesting some pathogens.



What happens when the skin is cut and blood escapes from the blood vessels?

a semi-solid blood clot is formed from liquid blood to seal up the cut and prevent entry of pathogens


What 'thing' has a critical role in blood clotting? What are they?

- platelets
- small cell fragments that circulate with red and white blood cells in blood plasma


How does the clotting process begin? What happens as a result of this?

- with the release of clotting factors either from damaged tissue cells (epithelial cells) or from platelets
- a cascade of reactions in which the product of each reaction is the catalyst of the next reaction


What does the cascading system help to ensure?

- that clotting only happens when it is needed
- also makes it a very rapid process


What happens in the last reaction in blood clotting? What is the result of this?

- fibrinogen, a soluble plasma protein, is altered by the removal of sections of peptide that have many negative charges
- this allows the remaining polypeptide to bind to others, forming long protein fibres called fibrin (insoluble).
- fibrin forms a mesh of fibres across wounds.
- blood cells are caught in the mesh and soon form a semi-solid clot. If exposed to air, the clot tries to form a protective svab, which remains until the wound has healed.


Draw a diagram showing the reactions initiated by clotting factors.

1. reactions initiated by clotting factors released by platelets or damaged tissue cells
2. prothrombin activator (prothrombin (inactive) --> thrombin (active))
3. fibrinogin (soluble) --> fibrin (insoluble)


What could happen if deposits of plaque in coronary arteries rupture? What is this called?

- blood clots form (coronary thrombosis), which may completely block the artery
- consequences = an area of cardiac muscle receives no oxygen and so stops beating in a coordinated way

- called: a heart attack


What is fibrillation?

uncoordinated contraction of cardiac muscle

(basically a heart attack)


Can the heart recover from fibrillation?

- yes, sometimes it starts beating again
- but severe heart attacks can be fatal as contractions of the heart stop completely


Sketch and label a diagram of a healthy artery. Sketch and label a diagram of a plaque lined artery. (p76)


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