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
