Exchange and Lymph Flashcards
what aspects of capillary structure increase diffusion?
they have thin walls and a large surface area to volume ratio
what are fenestrations?
theses are temporary channels that things can diffuse across
describe a continuous capillary
they contain no channels. they can have clefts (muscle) or have none (brain to prevent potassium entering)
describe a fenestrated capillary
they contain clefts and channels and are found in the intestine
describe a discontinuous capillary
there are clefts and massive channels (liver to allow proteins to enter)
describe clot formation in a blood vessel
clots form when blood in the capillary is slow. platelets are cell fragment which signal if they detect collagen and form a platelet plug. fibrinogen is converted to fibrin by thrombin to form the fibrin clot.
what does the endothelium produce as an anti-clotting mechanism?
> prostacyclin and NO to inhibit platelet aggregation
> tissue factor pathway inhibitor to stop thrombin production
what does the endothelium express as an anti-clotting mechanism?
> thrombomodulin which binds and inactivates thrombin
> heparin which inactivates thrombin
what doe the endothelium secrete as an anti-clotting mechanism?
tissue plasminogen activator, plasminogen digest clots
what are starlings forces?
water is pushed out of the capillaries by hydrostatic pressure which builds up the conc. in the capillaries. this increases the osmotic pressure that is pushing water back into the capillaries.
how does the structure of lymph capillaries move the lymph back to the heart?
the capillaries contan vlaves which create a one way movement of lymph back to the heart. the muscle contraction of muscle surrounding the lymph also causes lymph to move up the capillaries
what is oedema?
this is accumulation of excess fluid
what can cause oedema?
> lymphatic obstruction
raised CVP
hypoproteineamia
increased capillary permeability
how does kwashioeker cause oedema?
there is not enough proteins in the blood so the osmotic gradient is reduced and fluid is not reabsorbed
how does an immune response cause oedema?
blood is redirected to the region and cleft size is increased so white blood cells can leave the capillaries. hydrostatic pressure also pushes out the proteins so no osmotic pressure is built up.
