exchange and the lymphatic system Flashcards
how are capillaries specialised for diffusion?
lots of them
thin-walled
small diameter
why do capillaries have thin walls?
presents a small diffusion barrier
why do capillaries have a small diameter?
for a big surface area to volume ratio
what is the greatest distance a cell can be from a capillary?
100micrometres
what are the 3 types of capillary?
continuous
fenestrated
discontinuous
what are continuous capillaries?
capillaries with no clefts or channels, they may also have clefts only
where would you find capillaries with no clefts or channels (continuous)? why?
the brain, they help with the blood brain barrier
where would you find capillaries with only clefts ?
muscle
what are fenestrated cappillaries?
capillaries with clefts and channels
where are fenestrated capillaries found?
intestine
what are discontinuous capillaries?
capillaries with clefts and massive channels
where would you find discontinuous capillaries? why?
liver, to allow the transfer of large molecules like proteins
describe the process of clotting?
- damage to the endothelium wall exposes the collagen in the basement membrane.
- platelets adhere to this to form a platelet plug
- fibrinogen is converted to fibrin by thrombin.
- fibrin binds to the platelet plug forming a fibrin clot
what are the mechanisms the endothelium of blood vessels uses to stop clotting?
stops blood contacting collagen produces prostacyclin and NO produces tissue factor pathway inhibitor expresses thrombomodulin expresses heparin secretes tissue plasminogen activator (t-PA)
what do prostacyclin and NO do?
inhibit platelet aggregation
what does tissue factor pathway inhibitor do?
stops thrombin production
what does thrombomodulin do?
binds thrombin and inactivates
what does heparin do?
inactivates thrombin
what does tissue plasminogen activator do?
turn plasminogen in to plasmin and digests clot
how is diffusion self-regulating?
the more of a substance that is used the more is able to diffuse across to meet the demand, also works the other way around when demand is low
how is diffusion non-saturable?
there is no peak rate of movement of substances
moving through capillaries, why does diffusion of water out of the capillary decrease?
the hydrostatic pressure decreases
why does the movement of water into the capillaries increase moving further through the capillaries?
with water moving out of the cells because of hydrostatic pressure the oncotic pressure increases and more water moves in
on average how much water in lost due to hydrostativ force and how much is regained by oncotic pressure?
20L lost. 17 L regained per day
so 3 L remains and must be drained by the lymphatic system
what are some causes of oedema?
lymphatic destruction
raised CVP
hypoproteinemia
increased capillary permeability
what can cause lymphatic destruction?
filariasis (parasitic worm infects lymphatics), surgery
what can cause a raised CVP?
vetricular failure
what can cause hypoproteinemia?
nephrosis, liver failure, nutrition
what can cause increased capillary permeability?
inflammation eg. rheumatism
