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)