Circulation And Hemodynamics Flashcards
What is the site of the highest resistance and largest drop is pressure?
Arterioles
Composition of capillaries
Single layer of endothelial cells surrounded by basal lamina
How is perfusion of capillaries determined?
By metabolic needs of the tissue and the tone of the arteriolar smooth muscle
Velocity of blood flow
V=Q/A
Speed at which blood travels
Flow=speed and number of blood traveling
Flow equation
DeltaP/R
Poiseuille’s law
(8ln)/(piR^4)
Series resistance
Resistance is the sum of the forces
Parallel resistance
Resistance is 1/sum of the resistances and is lower than all individual resistances
Bruits
Heard when turbulent flow occurs in an artery or other vascular channel
Reynold’s number
Nr=(pdv)/n
Density
Diameter
Velocity
Viscosity
<2000 predicts laminar flow while >2000 predicts turbulent flow
Mean arterial pressure
2/3 DBP + 1/3 SBP
DBP + 1/3 pulse pressure
Arteriosclerosis
Plaque deposits form in arterial walls - decreases diameter and compliance of vessels, increases SBP, pulse pressure, and MAP (no large influence on DBP)
Lipid soluble microcirculation
O2, CO2. Driven by partial pressure gradient for that gas - also determined by the surface area of capillaries.
Water soluble microcirculation
Ions, glucose, AA
Diffusion doesn’t occur well. Limited movement between clefts of endothelial cells. Limits SA available for movement of molecules.
Osmosis of microcirculation
V important.
Driven by hydrostatic and osmotic pressure differences btwn lumen of vessel and interstitial space
Proteins in microcirculation
Generally don’t cross except in kidney and intestine where fenestrations in the capillaries will allow for limited movement of protein molecules
Starling equation
IV=Kf [(Pc-Pi)-(piC-piI)]
Kf
Determines magnitude of fluid movement
Pc
Favors filtration based on fluid pressure
Hydrostatic capillary pressure
Pi
Opposes filtration
Hydrostatic interstitial pressure
PiC
Opposes filtration
Capillary oncotic pressure
PiI
Favors filtration
Interstitial oncotic pressure
How will Pc impact lymph filtration
Pc can increase with venous pressure, heart failure, and ECF volume expansion and will cause an increase in lymph filtration
How will piC impact lymph filtration
piC will decrease from decrease plasma protein concentration, severe liver failure, protein malnutrition, or nephrotic syndrome and this will increase lymph filtration
How will Kf impact lymph filtration
Kf will be increase by burns or inflammation and will increase the lymph filtration
How does impaired lymphatic drainage affect lymph filtration?
It will increase it
Can be caused by standing for long periods, removal or LNs, and parasitic infections
Active hyperemia
Blood flow is proportional to metabolic activity I.e. blood flow is increased to exercising SKM
Reactive hyperemia
An increase in blood flow in reaction to a period of decreased blood flow
Myogenic hypothesis
Can explain autoregulation - states if vascular SM is stretched it will react and contract
Metabolic hypothesis
O2 delivery is matched to O2 consumption
local metabolic control is most important for which types of circulation
Coronary, cerebral, pulmonary, renal, and SKM when exercising
Sympathetic control is most important for which types of circulation
SKM at rest and skin circulation
Mechanisms for generating heat
Thyroid hormones (stimulate Na/K+ and increase metabolic rate) Sympathetic nervous system, shivering (started by posterior hypothalamus)
Mechanisms for dissipating heat
Coordinated by anterior hypothalamus to decrease symp outflow through arterioles and shunt blood to venous plexuses near surface of skin
Also increase sympathetic cholinergic activation of sweat glands
