Mejia's Microcirculation
Kf is influenced by what factors
# of pores and their size number of transporters number of perfused capillaries density of capillaries tightness of tight junctions
NFP equation
(Pc-Pi)-(pie c - pic i) sign determines direction + filtration -absorption number indicates velocity
explain why when traveling through a capillary there is first filtration and then absorption that occurs
initially the hydrostatic pressure is higher than the oncotic pressure - this results in filtration as fluid reaches the venule side, oncotic pressure is greater than hydrostatic pressure - this results in absorption
Pi
interstitial hydrostatic pressure produced by fluid in the interstitial flud pressure depends on volume of fluid in the space and compliance
what is the major determinant of lymph flow
interstitial hydrostatic pressure (Pi)
pie i
interstitial oncotic pressure made by any escaped proteins favors filtration
what direction does absorption occur
into the capillary
what happens to lymph flow when interstitial hydrostatic pressure reaches 0?
it reaches a max because flow gets opposed by external compression of larger lymph vessels by high Pi
fenestered capillaries
kidneys, intestines, endocrine glands, joints pores called fenestrae enhanced permeability to small hydrophilic molecules
the surface area for diffusion of ____ substances is much greater than the surface area of ___ substances
lipophilic hydrophilic
how does liver and renal disease lead to edema
loss of protiens
when is compliance low in interstitial fluid when is it high?
low at dehydration high when hydrated
name the general characteristics of capillary blood flow
low velocity intermittent direction is due to pressure gradients non uniform
continuous capillaries
muscle, skin, lungs, fat, connective/neural tissue tight junctions glycocalyx coat and basal lamina coat
passage of hydrophilic molecules
need pores to get through less surface area that it can diffuse through
what is the charge of albumin
negative
what is nutritive flow
occurs in active tissue requires great blood flow controlled by precapillary sphincters
what is Rouleaux formation
occurs only in microcirculation rare, when rbcs stack together increases viscosity and resistance
does exchange occur in post capillary venules
only some
What is Van't Hoff's Law?
osmotic pressure generated by charged solutes differs greatly from solutes that are neutral due to electrostatic interactions of ions with protiens
what direction does Pc favor
out of the capillary
where direction does filtration occur
out of the capillary
what are the three things that affect diffusion
permeability concentration difference surface area
pie c
plasma osmotic pressure due to proteins in plasma favors abosrption
define hydrostatic pressure
potential energy due to pressure exerted by a liquid
hydrostatic pressure (Pc) depends on the ratio of what
pre/post capillary resistances
what are precipitation factors of peripheral edema
reduction in plasma protiens increase in hydrostatic pressure increase in permeability lymph obstruction
purpose of capillaries
site of exchange
characteristics of terminal arterioles
smooth muscle less innervation greater control by vasodilation site of resistance
what determines the overall blood flow to particular bed when a sphincter is open
the radius of artery
what occurs when the Rpost/Rpre >1
there is either arteriolar dilation or venular constriction there is an increase in hydrostatic pressure
what is edema
accumulation of excess interstitial fluid in the tissues when filtration exceeds rate of lymphatic drainage
what does a pressure increase in Pa cause
affects capillaries less since more resistance is faced
what is the most clinical clinical example of Van't Hoffs law
albumin makes up 51% of concentration in blood but has a 65% effect on oncotic pressure
what occurs when the Rpost/Rpre <<1
arteriolar constriction or venular dilation there is a decrease in hydrostatic pressure
how does an increase in concentration gradient affect diffusion
as tissue is metabolically active the concentration gradient between the plasma and cell increases
what does a pressure increase in Pv cause
backflow into the capillary beds
discontinous capillaires
bone marrow, liver, spleen wide gaps permeable to very large molecules
how do burns or anaphylaxis lead to edema?
both increase capillary permeability
passage of lipophilic molecules
can pass through easily
Pc
capillary hydrostatic pressure
what occurs to these values when arterial vasoconstriction occurs Pc: NFP: what direction does fluid move?
dec dec absorption
what occurs to these values when the pressure of arteries is decreased? Pc: NFP the direction of movement?
dec dec absorption
what occurs to these values when plasma protein concentration decreases? Pie c: NFP: what direction does fluid move?
dec inc filtration
a decrease in the post/pre capillary resistance has what effect on hydrostatic pressure?
decrease
Arteriolar vasoconstriction has what effect on : ___ Pc ___ NFP (filtration/absorption?)
decrease decrease absorption
a decrease in Pa (hypovolemia) has what effect on ___ Pc ___ NFP (filtration/absorption?)
decrease decrease absorption
a decrease in plasma protein concentration has what effect on: ___ pie c ____ NFP (filtration/absorption?)
decrease increase filtration
what is the process by which majority substances cross capillary walls
diffusion
what three principles does hydrostatic pressure follow
equal in all directions pressures in the same horizontal plane of a fluid are equal increases with depth
an increase in Pv (CHF for example) has what effect on: ___ Pc ___ NFP (filtration/absorption?)
filtration
what is the lymphatic pump
fluid fills lymph capillaires smooth muscle in the wall contracts, this forces lymph through valve into next segment
Meta arterioles
go from small arterioles to venules have precapillary sphincters blood can be shunted in multiple paths
characteristics of small arterioles
highly innervated contain smooth muscle site of resistance
what occurs to these values when arterial vasodilation occurs Pc: NFP: what direction does fluid move?
inc inc filtration
what occurs to these values when the pressure of veins is increased? Pc: NFP the direction of movement?
inc inc filtration
what is non nutritive flow
includes meta arterioles but bypasses capillaries so little exchange occurs
administration of IV colloids has what effect on: ___ pie c ____ NFP (filtration/absorption?)
increase decrease absorption
edema can be caused an an ____ in Pc ____ in pie c
increase decreased
arteriolar vasodilation (histamine release) has what effect on: ___ Pc __ NFP (filtration/absorption?)
increase increase filtration
what occurs to these values when an IV colloid is given Pie c: NFP: what direction does fluid move?
increases decreases absorption
what does capillary recruitment result in
increases surface area and reduced diffusion distance
what determines which capillary beds get perfused
what precapillary sphincters are open
since the Ra >>> Rv what effect does this have on increases in either one?
when there is an increase in arteriolar pressure, Pc does not change as much since resistance holds back the fluid when there is an increase in venous pressure, Pc changes greatly since there is much less resistance to hold it back
what is the rate of fluid movement equation (FM)
FM = Kf x [(Pc-Pi)-(pie c - pic i)] where Kf is the filtration coefficient reflecting permeability of capillaries in that organ bed
what is the equation for diffusion
J = D x A (dc/dx) flow= diffusion x area x (concentration diff/distance traveled)