B1W4: Capillaries/Local Control Blood Flow Flashcards
Components microcirculation
- Arterioles and venuoles with smooth muscle
- precapillary sphincters
- metaarterioles–smooth muscle cells around capillaries
Flow in capillaries
Intermittent due to vasomotion (opening/closing of spinchters, contracting); tissue O2 determines this
Lymphedema
Edema from tumor restricting blood flow back from veins and causing increasing P
Structure of capillary wall
- slit pores that allow hydrophillic molecules in
- plasmalemmal vesicles for bigger hydrophillic proteins (at caveolae)
- endothelium and basement membrane for lipophillic molecules to go through
- fenestrae/aquaporins for H2O
Rate of Flow Determinants
- conc. gradient
- surface area (if capillaries opened or closed)
- diffusion coefficient
- dependent on orga; brain has tight junctions, liver lets anything in, intestines are in the middle and kidney, with fenestrae, lets ionic substances in
Components of interstitum between capillaries and cells
- Collagen fiber bundles
- Proteoglycan filaments
- Tissue gel that becomes free fluid in edema
Four Capillary Pressures (Starling Forces)
- Capillary pressure (PC): OUT capillary
- Interstial fluid pressure (PiF): IN capillary, normally neg. though and does opp.
- Interstial fluid colloid osmotic pressure (πiF): OUT capillary
- Plasma colloid osmotic pressure (πP): IN capillary, albumin
Calculating Net Filtration
(add forces moving out) - (add forces moving in) = net filtration
If answer +: net moving out
If answer -: net moving in
Net filtration in body
2 mL/min at .3 mmHg
Lymph catches and restores it so we don’t get edema, up to a point
Factors increasing lymph flow
- elevated capillary pressure
- decreased plasma COP (drinking too much, liver can’t work)
- Increased interstial fluid COP
- Increased permeability capillaries (allergic reactions)
- Lymph pump
Types of local, short-term regulation of blood vessels
- Metabolic autoregulation
- Functional hyperemia
- Reactive hyperemia
- Myogenic autoregulation
- Shear stress regulation
Metabolic autoregulation
Maintaining constant blood flow under constant metabolism due to an increase or decrease in pressure
–increase BP, vesels constrict
–decrease BP, vessels dilate
Functional hyperemia
Metabolism increases, we need more O2 so we increase blood flow
Intrinsic response
The only two ways to increase blood flow using the vessels
- increase pressure gradient
- decrease resistance (i.e. dilating)
Which organs have the most cardiac output?
Kidneys
Liver
Brain
Skin (thermoregulation–when hot)
Metabolic autoregulation theory 1: waste products
If blood flow is too low (i.e. a block upstream), metabolic waste products start to build up and THIS is what the vessel senses it needs to dilate for
Needs to wash these out
i.e. K+, lactic acid, H, CO2, adenosine
Metabolic autoregulation theory 2: O2
Due to an occlusion upstream, vessel senses it needs O2 so it dilates
When the blood pressure is getting low, senses it has too much O2, constricts
Both of these maintain blood flow as constant even as pressure changes
Reactive hyperemia
Excess tissue flow following occlusion, causing overshoot of blood due to repaying of oxygen debt
–this overshoot is proportional to amount of time the vessel was occluded for
i.e. pushing down on fingers, get white, let go and blood rushes back
Raynaud’s phenomenon
Fingers blanch and become numb in coldness
During rewarming, digits become bright red and hurt!
The low blood flow and deoxygenation leads to an overshoot of blood flow, aka reactive hyperemia
Primary: unknown, idiopathic cause
Secondary: scleroderma
Myogenic autoregulation
Common in small arterioles
Intrinsic regulation based on stretch of walls due to flow
Not densing flow directly; blood pressure increasing and therefore wall constricts to stop it and keep flow constant
Shear stress regulation
NO produced, causing vasodilation
- made from L argininge and activates guanylyl cylase, which makes cGMP (vasodilator)
LaPlace’s Law
Wall tension=pressure x radius
Increase radius, increase tension
Hypertrophy occurs (radius increases) in response to increased tension
