6. Defence Against Infectious Disease Flashcards
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?
A SUPER MEGA ULTRA PHAGOCYTE???
pus.
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.
