exchange and lymphatic system Flashcards
what is the wall of capillaries like?
only composed of endothelium- one cell thick
what is the gross structure of capillaries?
big surface area: volume ratio
specialised for exchange
every issue within 100 micrometre of one
thin -walled - small barrier for diffusion
small diameter
what are fenestrations?
pores in the endothelium of cells
what are clefts?
cell-cell junctions
what are the three types of capillaries?
continuous, fenestrated and discontinuous
what are the features of continuous capillaries and give 2 examples of them
only have clefts, some don’t even have clefts - e.g. brain, no clefts due to very tight nature of blood-brain barrier
clefts only- muscle
what are the features of fenestrated capillaries and give an example of where they can be found
have large pores in their membrane which increases their permeability, some clefts & some channels e.g. kidney
what are the features of discontinuous capillaries and give an example for where they are found
have very large channels and clefts e.g. liver as it produces proteins and they have to get into the bloodstream
what allows the blood to clot?
pooling of blood/ very slow flow
what is involved in blood clotting and what are the 2 components involved?
endothelium is involved in blood clotting.
2 components involved:
-platelet plug
-fibrin clot
describe the formation of these 2 things
if there is a tear/hole in the wall of the endothelium, circulating platelets in the blood are exposed to the collagen and send signals to recruit further platelets to form a platelet plug around it. On top of this, circulating fibrin in the form of fibrinogen in plasma, is converted to fibrin by an enzyme found in blood called thrombin. the fibrin forms a clot around the platelet plug.
what are 6 mechanisms which the endothelium uses to reduce chance of clots arising spontaneously?
prevent platelet aggregation:
-stops blood contacting collagen
-PRODUCES PROTACYCLIN & NO- both inhibit platelet aggregation
prevent clot formation:
-thrombomodulin- bind thrombin & inactivates it
-heparin- binds thrombin & inactivates it
-TFPA- stops thrombin production
-tPa - plasminogen –> plasmin = plasmin breaks down clots
what are the 3 main methods of exchange ?
diffusion, bulk flow and carrier
what are 4 characteristics of diffusion?
self-regulating
non-saturable
polar substances through clefts/channels
non-polar substances through cell membrane
what are the 2 main forces which impact bulk flow and describe them
oncotic pressure - this is the pressure which the proteins inside blood vessels exert which tends to draw water back in
hydrostatic pressure - the pressure inside hose pushing water out against walls, which results in water leaking out
most water leaks out at start when arterioles become capillaries and most water drawn back in at capillary-vein junction
