CH 25 of Guyton

7/30/2019 CH 25 of Guyton

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ABCJJKKMP- Batch 2017 Page 1

Lectured on: August 29, 2013

Lectured by: Dra. Felices Emerita Pascual - Perez

RENAL PHYSIOLOGY

Topic: THE BODY FLUIDS COMPARTMENTS : ECF & ICF

Maintenance of a relatively constant volume and a stable composition of the

body fluids is essential for homeostasis

Water Balance to maintain a steady state, water intake must equal water

excretion.

Average INTAKE per day 2300 mL

2100 mL from ingested

food and beverages

200 mL from metabolism

Average OUTPUT per day 2300 mL

100 mL feces (4%)

100 mL sweat (8%)

700 mL insensible losses via skin and lungs (25%)

1400 mL urine (60%)

BALANCE CONCEPTS

Balance is necessary, in the long-term,

to maintain life.

Fluid Loss = Fluid Intake

Electrolyte Loss = Electrolyte Intake

Fluid Intake: regulated by thirst mechanism, habits

Electrolyte intake: governed by dietary habits

Fluid Output: regulated mainly by kidneys

Electrolyte output: regulated mainly by kidneys

BODY FLUIDS COMPARTMENTS

FLUID BALANCE (ml/day)70 kg

Adult

TOTAL BODY WATER IN RELATION TO BODY WEIGHT: EFFECTS OF GENDER,

BODY BUILD AND AGE

Transcellular fluid compartmenta specialized type of ECF 1-2liter

- Synovial fuid- Peritoneal fluid- Pericardial fluid- CSF (cerebrospinal fluid)

BODY FLUID COMPARTMENTS

ECF ICF

20% of body weight = 14 L 40% of total body weight = 28 L

(++) Na+, Cl- and Bicarbonate ions Only small amount of Na+ and Cl-ions and almost no Calcium

Has small amount of Potassium,

Calcium, Magnesium phosphate and

organic acids

Proteins: Plasma > ISF

Large amount of K+ and PO4- ions.

Moderate quantities of Mg++ and

Sulfate ions

Proteins -4x greater than ECF


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BLOOD VOLUME

Both ECF & ICF Average blood volume = 5 L (7 % of body weight) 60% plasma, 40% RBC Hematocrit

- Fraction of the blood composed of RBC- Men 0.40- Females 0.36- Anemia low levels- Polycythemia excessive production

COMPUTATION OF BODY WATER

(for a 70 kg man)

Total Body Water (TBW)

= 60% or 0.6 x Body weight (BW)

42L

ECF ICF

=20% or 0.2 x BW =40% or 0.4 x BW

13L 28L

MEASUREMENT OF BLOOD VOLUME

Total Volume = Plasma volume1-Hematocrit

An average 70 kg man:

Total blood volume = 3.5 L / 1-0.40

= 5.8 L

Blood volume = 7% of body weight

Hct in male = .40

REGULATION OF FLUID EXCHANGE AND OSMOTIC EQUILIBRIUM

b/w ICF & ECF

The distribution of fluids between ECF and ICF is determinedmainly by the osmotic effect of smaller solutes.

- Sp. NaCl and other electrolyte acting across the cellmembrane

Involves semi-permeable cell membrane- Permeability: Water >>> NaCl- Thus water moves very rapidly across the membrane

so that the ICF remains isotonic with the ECF.

CONTROL OF BODY FLUID DISTRIBUTION

Distribution across cell membranes determined by osmotic forces (mainly

from electrolytes)

Distribution across capillaries determined by hydrostatic and colloid

osmotic forces.

BASIC PRINCIPLES OF OSMOSIS AND OSMOTIC PRESSURE

Osmosis Net diffusion of water across a selectively permeable membrane

from a region of high water concentration that has a lower water

concentration.

-The higher the solute concentration the lower the waterconcentration.

Rate of osmosis Rate of diffusion of water

WHAT IS THE DIRECTION OF OSMOSIS?

A.

Pure water

B.

C.

With solute

Osmole - refers to the number of osmotically active particles in a solution.

-

1 osmole is equal to 1 molecule of solute

1 mole of Glucose L = 1 osmole L 1 mole of NaCl L = 2 osmoles L 1 mole of Na2SO4 L = Osmoles L 1 milliosmole = 1 1000 osmole

ISF

of ECF

10.5L

Plasma

1/3 of

ECF

3.5L

*

* *

*

* *


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OSMOLARITY AND OSMOLALITY

Osmolality- Osmolal concentration of solution- OSmoles per kg of water (osm/kg H2O)

Osmolarity- Osmoles per literof solution (osm/L)

OSMOLARITY

Fluid Osmolarity:-

ECF: Na and Cl ions- ICF: 50% due to K+- Corrected osmolarity is 282 mosm/L

RELATION BETWEEN OSMOTIC PRESSURE AND OSMOLARITY

Osmotic pressure of a solution is directly proportional to theconcentration of osmotically active substances regardless of the

size of the solute/

Which has a higher osmotic pressure? Albumin, Glucose, NaCl

OSMOTIC PRESSURE : VAN HOFFS LAW

PRINCIPLES OF OSMOTIC EQUILIBRIUM

CALCULATION OF THE OSMOLARITY AND OSMOTIC PRESSURE OF A

SOLUTION

What is the osmotic pressure of a -.9% NaCl solution? Is this isotonic, hypotonic or hypertonic?

OSMOLARITY OF A 0.9% NaCl SOLUTION

OSMOLARITY

Plasma mosm/L ISF ICF

Total mosm/L 301.8* 300.8 300.8

Corrected** 282 mosm/L 281 mosm/L 281 mosm/L

Total osm.

Pressure at 37C

5443 5423 5423

*Slightly higher in plasma due to osmotic effects of plasma

proteins

**Correction factor (osmotic coefficient) for NaCl is 0.93

EFFECTS OF DIFFERENT CONCENTRATION OF IMPERMEANT

SOLUTES IN ECF ON CELL VOLUME

Tonicity of solution, refers to whether solution will cause a change

in a cell volume; depends on concentration of impermeant solute.

Isosmotic solution has same osmolarity as body fluids

Hyperosmotic higher osmolarity than body fluids

Hyposmotic lower osmolarity than body fluids

Osmolarity of solution refers to solution with higher or lower

osmolarity compared with Normal ECF without regard for

whether it can permeate the cell membrane.


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REVIEW: WHATS THE EFFECT OF SOLUTIONS OF CARYING

TONICITY ON RBC?

280 mOsm/L 200 mOsm/L 360 mOsm/L

QUESTIONS:

What is the osmolarity of a 5% glucose solution? (MW is 180g/mol)

Is the solution hyperosmotic, hypo-osmotic or isosmotic? What is a hypo-osmotic solution?

OSMOLARITY OF A 5% GLUCOSE SOLUTION

REMEMBER!!!

Water moves rapidly across cell membranes, thus osmolaritiesbetween ECF & ICF remain almost equal.

Cell membrane are almost impermeable to many solutestherefore the number of osmoles in ECF or ICF generally are

constant unless solutes.

WHAT ARE THE CHANGES IN THE FF VARIABLES AFTER GIVING 2.0 L OF

WATER I.V.?

ECF Volume? Increase

ECF Osmolarity? Decrease

ICF Volume? Increase

ICF Osmolarity? Decrease

WHAT ARE THE CHANGES IN THE FF VARIABLES AFTER GIVING 2L OF 3%

NaCl I.V.?

ECF Volume? Increase > 2.0 L

ECF Osmolarity? Increase

ICF Volume? Decrease

ICF Osmolarity? Increase


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SUMMARY

ABNORMALITIES OF ECF FLUID Na+ CONCENTRATION

ECF solute is 90% due to NaCl, hence an indicator of plasma osmolarity.

CONSEQUENCES OF HYPONATREMIA AND HYPERNATREMIA

Water moves in and out of cells cells swell or shrink

This has profound effects on the brain.- Neurologic function is altered- Rapid shrinking can tear vessels and cause hemorrhage- Rapid swelling can cause herniation because the skull

is rigid, the brain cannot increase its volume by more

than 10% without being forced down the neck

(herniation).

ABNORMALITIES OF BODY FLUID VOLUME REGULATION

ABN Cause Plasma

Na+ Conc

ECF Vol ICF Vol

Hyponatremic

Dehydration

Diarrhea,

vomiting,

adrenal insuff;

overuse of

diuretics,

Addisons

Hyponatremic

overhydration

Excess ADH,

bronchogenictumor

Hypernatremic

dehydration

Lack ADH,

Diabetes

insipidus,

excessive

sweating

Hypernatremic

overhydration

Cushingsm

primary

aldosteronism

HYPO/HYPER OSMOTIC REFERS TO PLASMA Na+ CONCENTRATION

EDEMA

Presence of excess fluid in the body tissues.INTRACELLULAR EDEMA

Depression of tissue metabolic systems(e.g. hypothyroidism)

Inadequate tissue nutrition(e.g. ischemia)

Inflammation of tissues (increased cellmembrane permeability)

EXTRACELLULAR EDEMA

Causes of increased interstitial fluid volume

Increased Capillary Filtration Failure of lymphatics to return interstitial fluid to circulation

3 Factors that can increase capillary filtration

1. Increased capillary hydrostatic pressure (Pc)2. Decreased plasma colloid osmotic pressure3. Increased capillary filtration coefficient (permeability) (Kf)

DETERMINANTS OF CAPILLARY FILTRATION


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XLymphatic

Failure = Edema

CAUSES OF INCREASED CAPILLARY FILTRATION

NORMAL FILTRATION

FILT = Kfx Net Filt Pressure

= 6.6 x ( 17.3 - (-3) - 28 +8)

= 6.6 x ( + 0.3)

= 1.89 ml/min

FILT = 2722 ml/day

Where does all of this fluid (and protein in it) go?

FUNCTION OF LYMPHATICS

CAUSES OF ECF EDEMA

Lymphatic blockage Infection Cancer Surgery Congenital absence of lymphatics

SAFETY FACTORS AGAINST EDEMA

Low compliance of interstitium when = 3 mmHginterstitial fluid pressure is negative

Increased lymph flow = 7 mmHg Washdown of interstitial protein = 7 mmHgat high lymph flow rates

TOTAL SAFETY FACTORY = 17 mmHg

NEGATIVE PRESSURE SUCKS. (If negative IFPr, IF volume does NOT

change much if +3 fluid start to accumulate), because tissue

became highly compliant,

LOW TISSUE COMPLIANCE AND NEGATIVE INTERSTITIAL FLUID

HYDROSTATIC PRESSURE

INCREASED LYMPH FLOW

EFFECT OF INTERSTITIAL FLUID PRESSURE ON LYMPH FLOW

Increases lymph flow 10-50x

Lymph


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PITTING VS NON PITTING EDEMA

Thumbprint - When the thumb press against the tissue area, it pushes

the fluid away from the area.

When tissue cell swells instead of interstitium, fluid do not move away

from the area.

WASHDOWN OF INTERSTITIAL PROTEINS

CONDITIONS CAUSING EDEMA

1. High capillary hydrostatic pressure

Excess fluid retention by kidneys- acute or chronic kidney fa ilure- glomerulonephritis- mineralocorticoid excess

Decreased arteriolar resistance- vasodilator drugs- autonomic insufficiency

Increased venous pressure- congestive heart failure- high output heart fa ilure (e.g. anemia)- -venous obstruction- venous valve failure- cirrhosis

2. Decreased plasma proteins

(low oncotic pressure)

Loss of proteins- burns, wounds

- nephrosis

- gastroenteropathy

Failure to produce proteins- malnutrition (kwashiorkor)

- cirrhosis

- analbuminemia

3. Increased capillary permeability

Immune reactions (histamine) Toxins Burns Prolonged ischemia Vitamin deficiency (e.g. vitamin C) Pre-eclampsia and eclampsia in

Pregnancy

4. Blockage of lymphatics

Cancer Surgery Infections (e.g. filaria nematodes)

FLUIDS IN THE POTENTIAL SPACES OF THE BODY

Pleural, peritoneal, pericardial, synovial cavities Fluid is exchanged between the capillaries and the potential

spaces

Lymphatic vessels drain protein from the potential spaces Effusion- Edema fluid in the potential spaces- Abdominal cavityascites- Normal Interstitial hydrostatic pressure of

Pleural cavity (-) 7 to (-) 8 mmHg Pericardial cavity (-) 5 to (-) 6 mmHg Joint spaces (-3) to (-) 5 mmHg

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CH 25 of Guyton