capillary circulation Flashcards
purpose of capillaries
- exchange fluid, nutrients, electrolytes, hormones, wastes, etc between blood and interstitial fluid
- have thin walls with pores to allow for passage of water and molecules
vasomotion
- intermittent blood flow thru capillaries based on contractions of metarterioles and precapillary sphincters (in the arterioles that have smooth muscle that can contract- therefore it’s an upstream mechanism from the capillaries)
- can allow for complete closure of capillaries
- purpose: to allow for shift in blood flow for areas in need
- makes sure to INCREASE SURFACE AREA AND DECREASE VELOCITY TO ENABLE EXTRA OXYGENATION OF THE AREA IN NEED
what does blood flow thru capillaries depend on?
- what can get thru upstream- is thru arterioles and sphincters/metarterioles etc
- the constriction of the upstream elements is directly related to what’s going on IN THE TISSUE- is tissue needs it, then yes, if not, then no!
in skeletal muscles what does “work” do to pO2, pCO2, pH, and flow?
brain?
heart?
pO2 = decreases, pCO2 increases, decreases pH, and flow increases = get vasodilation
brain= increase CO2, decrease pO2, increase adenosine
heart= increase adenosine, increase CO2, decrease O2, decrease pH
state whether this constricts or dilates: epi: norepi: Dopamine: Histamine: Ach: Angiotensin II: kinins: ADH/Vasopressin: VIP (vasoactive intestinal peptide):
epi: both- alpha constricts and beta dilates
norepi: constricts
Dopamine: dilates in renals but constricts elsewhere
Histamine: dilates
Ach: dilates
Angiotensin II: constricts
kinins: dilates
ADH/Vasopressin: constricts (PRESSIN- constricts)
VIP (vasoactive intestinal peptide): dilates
state whether this constricts or dilates: adenosine, adenine, nucleotides- hypoxemia- H and K- hypercapnia- Krebs cycle intermediates- endothelin- EDRF (NO)-
adenosine, adenine, nucleotides- both hypoxemia-dilates H and K- dilates hypercapnia (lots of CO2)- dilates Krebs cycle intermediates- dilates endothelin- constricts EDRF (NO)- dilates
what dictates good diffusion across a capillary
-lipid solubility and small size to get thru pore
water soluble things need pores to get in when lipid soluble things can just use direct diffusion
reabsorption vs filtration
reabsorption- bringing things back INTO the blood
filtration- bringing things out of the blood
hydrostatic pressure vs colloid pressure
hydrostatic- pressure generated by fluid itself
colloid is pressure generated by the material in the fluid
what will increased fluid pressure in the capillaries do?
-moves fluid out of the capillaries
besides an increase in fluid pressure in the capillaries, what also draws blood out into the interstitium?
the low interstitial fluid conc- this is the function of the lymphatic system!
what does capillary oncotic pressure do?
- tends to move fluid in
- increase oncotic pressure, increase fluid into the capillaries
if there is a lot of proteins etc in the interstitium, what does that do with the capillaries?
- causes fluid to move out of the capillaries
- therefore, to keep fluid in, you increase oncotic pressure of the capillaries (adding albumin)
how do you calculate the total net pressure on capillaries?
if net>0 what does that mean? net<0?
Pressure in the capillaries (hydrostatic) pushing fluid out - hydrostatic pressure on the outside of the capillaries (usually neg so you add)pushing fluid back in - colloid pressure keeping stuff in + the interstitial pressure pulling stuff out \+--+ net>0 -fluid moving out net< 0- fluid moving in => NEGATIVE IS IN
If the net hydrostatic pressure is less than the net oncotic pressure, what occurs
-it’s a signal to move fluid OUT of the capillaries
if you have an increase in plasma proteins, what is that a trigger for
reabsorption
if hydrostatic pressure is less than oncotic pressure, what does that signal
reabsorption
if you have an decrease in plasma proteins, what does that trigger
filtration (loss of fluid)
interstitial edema
- excess filtration either from increased Pc (hydrostatic pressure) or decreased pieC which is colloid pressure
what can cause a decrease in colloid pressure
pregnancy, starvation, nephrotic syndrome
what can cause a increase in hydrostatic pressure
-standing, heart failure, venous thrombus
