Arteries, Veins, and Microcirculation Flashcards
WHat vessels have the highest wall thickness to lumen diameter?
precapillary spincters
arterioles are close
elastic modulus
force per unit area that is required to stretch a material to 2x its original length or the slope of the stress/strain relationship to the right
What happens to arterial compliance with age?
decreases with age
less elastin and mroe collagen
Windkessel effect
the walls of the aorta act as a secondary pump by stretching out during systole and then continuing to pump blood during diastole
this effect wears off with age
Laplace’s law
the pressure inside a cylindrical or spherical vessel exerts a distending force on the wall proportional to the magnitude of the pressure and the radius
T = (Pi - Pt)/h
Pi = intravascular pressure
Pt = tissue pressure
pulse pressure
systolic pressure - diastolic pressure
physical factors that affect arterial blood pressure
arterial blood volume and compliance
factors affecting diastolic presssure
resistance - run off rate
compliance of the aorta
systolic pressure
heart rate
mean arterial pressure equation
MAP = CO x TPR
runoff
blood flowing away from the heart to the peripheral arteries and tissues
the greater the runoff, the lower the pressure
What is the relationshi between wave frequency of blood flow and dampening?
low frequency waves move more slowly but undergo less dampening
high frequency waves move faster but undergo more dampening
What does decreasing distensibility do to rate of flow and dampening?
it increases rate of flow and causes more dampening
metarterioles
discontinuous single layer of vascular smooth muscle cells generally not innervated
characteristics of blood flow through capillaries
low velocity
intermittent due to vasomotion
changes direction due to pressure gradients
not uniform
Roleaux formation
Roleaux formation
“stack of coints” arrangement of RBCs
vasomotion
spontaneous contraction and relaxation of precapillary sphincters
increased metabolic activity increases the time that precapillary sphincters are open
decreased oxygen delivery has the same effect
capillary hydrostatic pressure (Pc)
major determinant of fluid movement
determined by arterial pressure, venous pressure, and the ratio of venular to arteriolar resistance
Pc = [(Rv/Ra)*Pa + Pv]/[1 + (Rv/Ra)]
How does increasing pre/post pressure affect capillary hydrostatic pressure?
decrease
How does decreasing pre/post pressure affect capillary hydrostatic pressure?
increased
interstitial hydrostatic pressure
changes only slightly except in cases of lymphatic blockage or increased capillary permeability
normally around -1 mmHg
osmotic pressure
favors absorption
about 25 mmHg for water to enter the capillary due to the higher concentration of plasma proteins
pi = sRT (CI - CO)
What protein contributes the most of the plasma oncotic pressure
albumin - 51%
disproportionately large based on concentration
Starling’s Law for capillary fluid movement
fluid movement = k[(Pc + pii) - (Pi + pip)]
normally the first half fluid leaves (20L) and the second half is reabsorption of water (18L)
the remainder draings through the lymphatics
lymph
fluid and other plasma proteins that accumulate in the extravascular space
composition similar to plasma
flow depends on interstitial hydrostatic pressure
factors that predispose one to edema
increased capillary pressure
increased capillary permeability
decreased plasma protein concentration
excessive protein excretion, excess salt and fluid retention
lymphatic blockage
