Exchange and the Lymphatic System Flashcards
What type of vessels are capillaries?
exchange vessels
How are capillaries specialised for diffusion? (3)
- many of them (larger cross sectional surface area)
- thin walled
- large surface area:volume ratio
What are the 3 types of capillary?
- continuous
- fenestrated
- discontinuous
Continuous capillaries have ______ junctions.
leaky
Where would you find capillaries with no clefts or channels i.e. continuous?
Why?
Brain
Forms the blood-brain barrier, selective in what can diffuse across.
Where would you find capillaries with only clefts only between endothelial cells i.e. juncrtions?
muscle
Where are fenestrated capillaries found?
kidneys, intestines
Where would you find discontinuous capillaries?
Why?
liver
to allow the transfer of large molecules like proteins.
What is meant by diffusion being self regulating, in terms of concentration gradients?
if the cell starts to utilise more molecules e.g. O2 during exercise, then you get a larger concentration gradient between the cell and ECF to diffuse more oxygen i.e. the more that is used, the more that is supplied.
What is meant by saying that diffusion is non-saturable?
there is no limit to diffusion i.e. the higher the concentration gradient, the more will diffuse across the membrane.
there is no peak rate of movement of substances.
Why can polar substances not diffuse easily over the blood-brain barrier?
There are no clefts or channels, they require transporters as polar substances do not dissolve in liquids.
What is the term given for the mass exchange of fluid between capillaries and ISF?
bulk flow
Hydrostatic pressure _____________ the leaky capillaries. That builds up an __________ pressure which __________.
pushes fluid out through
osmotic (oncotic)
draws fluid back in
The balance of these hydrostatic and osmotic pressures is known as ___________.
Starling’s forces
Moving through capillaries, why does diffusion of fluid out of the capillary decrease?
the hydrostatic pressure decreases
What simultaneously builds up as fluid leaks out the capillaries due to hydrostatic pressure?
Why is this?
Oncotic pressure
Fluid leaving through leaky clefts, takes big solutes with in, these solutes build up another conc/pressure gradient = Osmotic (oncotic) pressure, it draws water back in to the plasma.
On average, how much water in lost due to hydrostatic pressure and how much is regained by oncotic pressure?
20L lost
17L regained
What happens to the excess 3L of fluid not diffsued back into the capillaries?
It is drained by the lymphatic system
What can happen when the lymphatic system becomes overwhelmed?
Peripheral oedema
Outline some of the causes of oedema. (4)
- lymphatic obstruction
- raised CVP
- hypoproteinemia
- increased capillary permeability
Describe how lymphatic obstruction can lead to oedema.
Give examples of how lymph vessels can become obstructed.
- leads to pressure build up (hydrostatic) within lymphatic vessels.
- more lymph leaks from the channels = oedema
filariasis, surgery, elephantitis (worms living in vessels)
What can lead to a raised CVP?
How can this lead to oedema?
ventricular failure
- ventricular failure can lead to back flow of blood into the lungs
- this increases hydrostatic pressure, causing oedema
What can cause hypoproteinemia?
Why does this lead to oedema?
due to nephrosis, liver failure, nutrition
- take malnutrition
- no proteins in the diet, lose water and don’t draw it back
- builds up osmotic pressure, presents as oedema
What can cause increased capillary permeability?
inflammation eg. rheumatism
