exchange in, and the control of, peripheral tissues Flashcards
what features of the capillaries make them specialised for exchange?
many of them - Every tissue within ~100 µm of one, so does not take long for 02 and C02 to diffuse in and out cells
very thin walled
small diameter - means big surface area: volume ratio
describe continuous capillaries?
continuous have leaky junctions which allow water and some molecules to cross
some continuous can have no clefts or pores (such as in the brain because of the blood-brain barrier) so limits what cant get into brain
some have clefts only (e.g. muscle and most other capillaries)
what are the differences between clefts and pores?
clefts are between epithelial cells, pores are across them
describe fenestrated capillaries?
they have large pores
Clefts and pores e.g. intestine and kidney, specialised for fluid exchange
describe discontinuous
they have clefts and massive pores, this allows proteins to move across into the bloodstream in the liver
what in an example of a carrier-mediated protein?
glucose transporter in the brain, BB barrier heavily controls what goes in and out brain
exchange occurs via bulk flow as well as diffusion, what determines this?
Determined by starling’s forces (look over the diagram in ppt 7.1), as blood moves from arterioles - capillary, more water leaves to facilitate change in pressure, but this increases protein conc. so towards end of capillary as it goes into a venule it drags in more water.
can be worked out using net filtration pressure
(HC - HIF) - ((Pi)C - (Pi)IF)
what can oedema be caused by?
raised central venous pressure (CVP) - can be due to ventricular failure (example of LV failure, where right side works fine so blood accumulates in the lungs, leading to pulmonary oedema)
lymphatic obstruction - due to filariasis (worm in lymph node) and surgery
hyperproteinaemia - due to nephrotic syndrome (too much protein leaking out so pressure cant be built up to bring water back into capillary), liver failure, malnutrition
increased capillary permeability - Inflammation e.g. rheumatism
bulk flow results in the loss of around 3L of fluid a day, where does this go?
lymphatic system
what does Darcy’s law state?
flow is equal to change in pressure (change in pressure can be put as Mean arterial pressure when applying to systemic circulation) divided by resistance
(for to get flow through tube, need higher pressure at one end and lower at other)
what do we use to calculate resistance?
Poiseuille’s law - (viscosity x length x 8)/(r^4 x pi)
when calculating MAP, why can we exclude CVP from the equation?
because it is so small it doesn’t have much an effect
MAP is very important, it is the driving force pushing blood through the systemic circulation
how do we work out MAP?
MAP = CO x TPR
So varying the radius of resistance vessels is also used to control TPR and therefore regulate MAP
