MEDICAL PHYSIOLOGY SESSION 1

PRINCIPLES OF FLUID VOLUME AND REGULATIONCHAPTER 5-BORON BOULPAEP

REVIEW CHAPTER 1-LINDA COSTANZO

DR. KASHIF AHMAD, MBBS, MS, MS (MEDL), PHD

UNIVERSITY OF ILLINOIS

M1 STUDENTS AT URBANA CHAMPAIGN

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BODY FLUIDS AND WATER BALANCE

• DIFFERENTIATE BETWEEN THE FORCES OF DIFFUSION, OSMOSIS, FILTRATION AND

CONVECTION ON WATER FLOW.

• CALCULATE AND ESTIMATE PLASMA OSMOLALITY AND COMPREHEND HOW FLUID

OSMOLALITY IS IMPLEMENTED IN THE REGULATION OF FLUID VOLUMES.

• EXPLAIN THE THREE MAJOR STATES OF RESPECTIVELY DEHYDRATION AND

OVERHYDRATION. IDENTIFY AT LEAST TWO MAJOR CAUSES OF EACH OF THESE STATES.

• DIFFERENTIATE BETWEEN THE TERMS OSMOLE, OSMOLARITY, OSMOLALITY AND TONICITY.

LIST THE TYPICAL VALUE AND NORMAL RANGE FOR PLASMA OSMOLALITY.

• DEFINE THE DONNAN EQUILIBRIUM AND LIST THE RESULTING CHARACTERISTICS.

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ICF VS ECF

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60-40-20 rule, 60 (TBW) of which 40 in ICF and 20 in ECF

3/4 1/4

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Na+

K+

Na+

Cl -

HCO3-

Cl -

HCO3-

Ca+Ca+

Na+ = HCO3-/ Cl -K+ Proteins

phosphates Mg2+ =

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GIBBS DONNAN EQUILIBRIUM

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TYPES OF TTRANSPORT

• SIMPLE DIFFUSION

• FACILITATED DIFFUSION

• CARRIER MEDIATED

• COTRANSPORT

• COUNTER-TRANSPORT

• ACTIVE TRANSPORT

• PRIMARY

• SECONDARY

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• STOKES-EINSTEIN EQUATION (SMALL SOLUTES MOVE HAVE HIGH

DIFFUSION COEFFICIENTS)

• P IS PERMEABILITY HERE K IS

PARTITION COEFFICIENT, BE CAREFUL

WITH “K” WHICH IS BOLTZMAN

CONSTANT IN STOKES EINSTEIN

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FICK’S LAW OF DIFFUSION

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J=Pa (C1-C2), where P is

permeability and “a” is surface

area, you can call “J” FLUX or

FLOW”

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OSMOSIS• OSMOLARITY=NO. OF PARTICLES X

CONCENTRATION

• REFLECTION COEFFICIENT

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gxC

CELL VOLUME REGULATORY MECHANISMS

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Courtesy NIPS Dept of Cell Physiology

Organic osmolytes such as sorbitol and inositol are gained (RVI) or lost (RVD)

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TONICITY

C=n/V

REMEMBER PROTEINS EXERT ONCOTIC/COLLOIDAL OSMOTIC PRESSURE, they

attract water they are a pull force, they don’t move much and are negatively

charged. They keep fluid inside compartments. If you lose proteins fluid could

follow. Also, tonicity is not osmolarity! You could relate effective osmotic

pressure to tonicity.

Osmotic water flow is the product of osmotic driving force and water

permeability which is called hydraulic conductance of filtration coefficient (Kf)

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SHIFTS OF WATER BETWEEN BODY FLUID COMPARTMENTSTO MAINTAIN OSMOLARITY CHANGE

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BASIC METABOLIC PANEL

• MEASURES ELECTROLYTES

• LAB REPORTS CRITICAL FOR DIAGNOSIS AND TREATMENT

• CALCULATING PLASMA OSMOLARITY=

• NORMAL PLASMA OSMOLALITY=285-295 MILLIOSMOLES/LITER

• MEASURED OSMOLARITY (MO)-CALCULATED OSMOLARITY, ALLOW UP 10, IF

> THAN 10 MEANS ABNORMALITY, THIS IS REFERRED TO AS OSMOLAR GAP

2 x[Na+] + Glucose/18 + BUN/2.8BUN is Blood Urea Nitrogen

2 x[Na+] + 10 in the ER to speed up the calculation

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Na balance is the key for fluid balance

CLINICAL APPLICATIONS

• DISCUSS VOLUME OSMOLARITY GRAPHS IN SIADH, DIARRHEA,

SWEATING, DEHYRDRATION, ADDISON’S DISEASE

• PLASMA EXPANDERS IN ER

• DRUG PERMEABILITY

• CONDITIONS WHERE OSMOLAR GAP IS INCREASED

• WHAT WILL HAPPEN IN PATIENTS WHERE THE BODY LOSES

PROTEINS? (KWASHIORKOR DISEASE, NEPHROTIC SYNDROME ETC)

• DEFECTS IN TRANSPORTERS, CHANNELOPATHY

• FLUID RETENTION AND HYPERTENSION19