L14 Capillary Exchange Flashcards
what is capillary hydrostatic pressure
required to exchange substances/fluids across cap network
(aka allows capillary exchange)
how is capillary structure adapted to be able to exchange
> short diffusion distance
- thin walls (1micrometer)
- small diameter (8micrometers) -> RBC all go in single file through it, and have direct contact with wall
- close proximity
- decreases diff distance, therefore diff time
> blood flows slowly
- due to large cross sectional area (largest area of all vessels)
- large surface area for exchange
= 10+ billion capillaries
- ~600square metres
what is the 3 types of capillaries
> continuouse - most caps
> fenestrated
(have water filled pores) - in endorcrine organs, intestine, kidneys
> sinusoid
(large clefts between endothelial cells and incomplete BM)
- free exchange of water and larger solutes eg plasma proteins
during substance exchange across cap walls, what molecules move out into cells and what moves in into caps (down pressure and conc gradients)
OUT=
water
O2
AAs
Glucose
Ions
IN=
water
CO2
waste molecules
ions
what are the 3 principle transport mehcanisms in cap exchange
> diffusion
- through endothelaial cell membrane, ion cannels, or clefts/pores
> bulk flow
- through clefts/pores
- down pressure gradient by filtration/osmosis
> transcytosis
- vesicular transport
what are the routes that substances can DIFFUSE via and what are they
through endothelial membrane:
- lipid soluble gases & moelcules
- eg O2 CO2 fatty acids
through channels
- ions
- eg Na+ Ca2+ etc
between endothelial cells (water filled pores)
- small water soluble molecules
- eg glucose urea AAs
what are the routes that substances can travel via transcytosis via and what are they?
in vesicles through the endothelial cell
larger macro molecules eg glycoproteins, insulin
what are the routes that substances can travel thtough bulk flow via and what are they
through clefts/pores
moving down pressure gradients
water soluble molecules only - e.g. water, ion, nutrients, waste
what’s it called when things move into the cap lumen via bulk flow
reabsorption
what’s it called when things move into the interstial fluid via bulk flow
filtration
what is bulk flow determined by
the net pressure difference across cap walls
what 4 forces influence fluid and solute movement
capillary hydrostatic pressure
interstitial fluid hydrostatic pressure
blood colloid osmotic pressure
interstitial fuid colloid osmotic pressure
what is cap hydrostatic pressure
the BP exerted on cap walls pushing fluid out
decreases along capillary
what is interstitial fluid hydrostatic pressure
the presssure exerted on outer cap wall by the IF, pushing fluid in
generally negligable (~0mmHg)
what is blood colloid osmotic pressure
the plasma osmotic pressure pulling fluid into caps
affected by blood volume
what is interstitial fluid colloid osmotic pressure
osmotic pressure of interstitial fluid pulling fluid out
generally negligable
what is net filtration pressure
determines whether fluid moves in or out of cap
NFP = net hydrostatic pressure - net osmotic pressure
NHP = cap hydrostatic pressure (CHP) - interstitial fluid hydrostatic pressure (IHP)
NOP = blood colloid osmotic pressure (BCOP) - interstitial fluid colloid osmotic pressure (ICOP)
if CHP>BCOP
+ve NFP
so filtration occurs
if BCOP>CHP
-ve NFP
reabsorption
what is the mmHg range the CHP goes through along the cap
35 - 18mmHg
due to resistance the blood faces as it moves along
what is the mmHg range the BCOP goes through along the cap
trick question heh
BCOP is constant
cuz the pressure is formed by plasma proteins which dont move cuz theyre too big
so the pressure stays around 25mmHg along the cap
what is the consequence of the max filtration pressure being greater than the max absorption pressure?
the point where they cross over at equilibrium is towards the venous end
this means for filtration takes place than absortpion
see onenote
on average how much fluid is filtrated a day trhough caps in L
24L/day
on avg how much fluid absorbed a day through caos in L
20.4 L/day
what could be an effect of high BP of NFP
CHP rises
so NFP rises
incerased filtration
fluid collects in extremities
systemic oedema
effect of haemorrage on NFP
CHP decreases
NFP decreases
favours reabsorption
increases BP & cardiac outpput (to compensate for blood loss)
effect of dehyrdration on NFP
reduction in blood volume = more conc of plasma proteins
so higher BCOP
so NFP decreases
increased reabsorptions
so fluid taken up from tissue into blood stream (to delay onset of symptoms)
effect of tissue damage (eg sprained ankle) on NFP
ICOP drops - cuz caps are more leaky and plasma proteins escape into interstiitial fluid
NFP increases
so filtration increases
local swelling around area (oedema)
in pulmonary circulation, how is blood flow adapted to engance O2 absorption compared to other organs
other organs vessels dilate when O2 falls to enhance O2 absoprtion
in lungs, arterioles contrict in regions of low O2 to shunt blood flow to O2 rich areas
how in the pulmonary circulation is it adapted so that gas wxchange occurs constantly
pulmonary vascular resistance is very low
- arterioles are shorter, wider and have thinner walls
CHP is lower than in systemic
(10mmHG compared to 35 mmHg)
- this is caused by the much lowere resistence mentioned before
arteries are more distensible (expandable)
- so any increase in cardiac output can be accomodated without too much increase in pressure
what is the CHP to BCOP relationship like along the whole vessel in the pulmonary circulation
CHP (10) < BCOP (25) along whole cap length
which means fluid absorbed along the whole cap length
in pulmonary circulation, what would happen is the CHP exceeded 25mmHg
fluid starts leaking into alveoli
pulmonary oedema
no good
how does the coronary circulation differ from systemic in terms of blood flow
when everywehere else the release of adrenaline causes vasoconstriction
in the coronary arteries, it’ll promote vasodilation
because of beta adrenergic receptors (see L13)
how does coronary blood flow get affected by the cardiac cycke
during ventricular systole, the left coronary artery acc get cut off and flow is restricted
blood flow much faster in diastole
see onenote for diagram
what happens to compensate for the shut off in blood spply during systole in the cardiac vessels
cardiomyocytes have very high O2 reserves
the myocardium has high cap density - so increases O2 extraction
caps have few arterial collaterals* (unsure what this is) - so blood flow moves more efficiantly
in cerebral circulation, what occurs when theres vasoconstriction in the periphery
vasodilation of the cerebral vessels
must ensure blood flow presereved always
how much cardiac output does the brain consume and why is this odd
well its not odd, it makes sense cuz it needs more blood
but it consumes 12% or CO for its 2% body mass
what is the flow rate in the brain
750ml/min
unlike cardiomyocytes, why do neurons need sm O2
they have poor metabolic reserves
so they need constant flow of O2, cant survive on their own
how many arteries supply the brain
4
then they anastomose inside the cranium
