THE THE MICROCIRCULATION.MICROCIRCULATION.MAIN CONCEPTSMAIN CONCEPTSGuido E. Santacana Ph.D.Guido E. Santacana Ph.D.

ProfessorProfessor

Dept. of PhysiologyDept. of Physiology

MICROCIRCULATIONMICROCIRCULATION STRUCTURESTRUCTURE LAW OF LAPLACELAW OF LAPLACE TRANSCAPILLARY EXCHANGETRANSCAPILLARY EXCHANGE STARLING’S HYPOTHESISSTARLING’S HYPOTHESIS LYMPHATICSLYMPHATICS

Structure of the Structure of the MicrocirculationMicrocirculation

Smoothmuscle

Arteriole

Venule

Metarteriole

Capillary

Endothelial cells

Precapillarysphincters

Ultrastructure of a Ultrastructure of a CapillaryCapillary

Lumen

Intracellular channels

Endothelial cell 1

Endothelial cell 2

Basement membrane

Nucleus

Intercellular cleft

5-10 m

LAW OF LAPLACELAW OF LAPLACE

T = P x r/wt

Tension = Pressure x Radius / wall thickness

Why do the capillaries in our feet don’t just burst from thepressure (about 100mmHg)?

How does Laplace Work?How does Laplace Work?

Less wall tension with Less wall tension with smaller radius?smaller radius?

FLOW AND DIFFUSION LIMITED FLOW AND DIFFUSION LIMITED TRANSPORTTRANSPORT

PARTICLE SIZEAND FLOW

CELL

FLOW LIMITED PARTICLE SIZE &DISTANCE

CELL

DIFFUSION LIMITED

REFLECTION COEFFICIENTREFLECTION COEFFICIENT

oncotic pressure = o RT (Ci - Co)

water=0 albumin=1

RT= gas and temperature constantsCi= concentration insideCo= concentration outside

REFLECTION COEFFICIENT = ACTUAL OSMOTIC FLOW/ THEORETICAL

CAPILLARY FILTRATIONCAPILLARY FILTRATION

HYDROSTATICFORCES

OSMOTIC FORCES

ARTERIAL PRESSUREVENOUS PRESSUREPRE-POST CAPILLARY RES.INTERSTITIAL FLUID PRESSURE

ONCOTIC PRESSURE

ALBUMIN

BALANCESTARLING’S HYPOTHESIS

Qf = k (Pc + i) - (Pi + p)

Graphic Representation Graphic Representation of Capillary Filtrationof Capillary Filtration

Capillary Filtration in Capillary Filtration in Various Clinical ConditionsVarious Clinical Conditions

A B

C D

What I cannot forget What I cannot forget about Microcirculation about Microcirculation

Four Forces known as Starling ForcesDetermine Fluid Movement Across the Capillary Membranes.

Pc= Capillary Pressure Tends to move fluid out of the capillaryPi= Interstitial Fluid Pressure Tends to move fluid into the capillary.Πc = Plasma Colloid Osmotic Pressure Tends to cause Osmosis of fluid into capillary.Πi = Interstitial fluid colloid osmotic pressure Tends to cause osmosis of fluid out of the capillary.Net Filtration Pressure = Pnet= ((Pc-Pi) – (Πc- Πi))

More things that I cannot More things that I cannot forget about the forget about the microcirculationmicrocirculation

EDEMA or excess fluid outflow into the interstitium is commonlycaused by :

Capillary Pressure ( Pc ; Heart Failure)

Plasma Proteins ( Πc ; Nephrotic Syndrome, liver failure)

Capillary Permeability ( Kf ; Toxins, infections, burns)

Interstitial Fluid Colloid Osmotic Pressure ( Πi; lymphatic blockage)

Net Fluid Flow = Pnet (Kf)

Pitting Edema of the FeetPitting Edema of the Feet

A Pit forms where theskin is pressured. It mayremain there for a few minutes

The Lymphatic SystemThe Lymphatic System

Elephantiasis or Elephantiasis or Lymphatic FilariasisLymphatic Filariasis