MCQs: Fluid and electrolyte balance

Fluid and electrolyte balance

Body fluid and compartments

Factors affecting total body water

1) Age - with increasing age total body water level goes down
2) Gender - females have more body water than males
3) Fat content - with increasing Fat level TBW level goes down
Water Balance

Water gain = water Loss
3L/day = 3L/day
Over hydration - gain > loss
Dehydration - gain < loss

Why Infants & children more prone to dehydration

Vomiting Diarrhea ----------------------------------------- dehydrated

ECF/ ICF : Infants & Children > adults

ECF volume : Infants & Children < adults

Possibility of H2O loss : ECF > ICF

Dehydration develops

1) More rapidly & is

2) Frequently more severe in children than adults

Distribution of electrolytes

	ICF	ECF
Major Cation (+)	K⁺	Na⁺
Major anion (-)	PO₄^3- Prot^-	Cl^-

Dilution principle

1. A known amount of substances (x) introduced to the concerned body of fluid compartment & allowed to equilibrate.

2. After equilibrium is reached concentration in the sample is measured (C) volume of body fluid compartment (V) is calculated

V= x / C

Characteristics of the substances used
1. Non toxic
2. Easily measured
3. Distribution limited to the compartment
4. Mix evenly throughout the compartment
5. Not changed or lost in time taken for equilibrium to reach or amount changed or lost is known
6. Compartment should be accessible for sample collection
7. Must not have an effect on its own on body fluid distribution.

Measurement of volumes of body fluid compartments

TBW - D2O,T2O, aminopyrine

ICF - TBW-ECF

ECF - radioactive inulin(most accurate)

Mannitol

Sucrose

Radioactive Cl- / Br-

Plasma - dyes which bound to plasma proteins ,Serum albumin labeled with radioactive iodine

TBV - 100 × plasma volume / 100 – Hematocrit

RCV - TBV- plasma

RBCs tagged with 51Cr

Interstitial fluid - ECF- plasma

Dilution principle

Movement of substances across biological barriers
Mechanism

Examples

1. Diffusion Simple Facilitated	Gases O₂, CO₂ Lipid soluble substances glucose
2. Active transport І ry П ry	Na⁺/K⁺ ATPase Na⁺/glucose (SGLT)^,Na⁺/ bile salt, Co transporters
3. Filtration	Glomerular filtration
4. Osmosis
5. exocytosis	Nerve impulse transmission
6. endocytosis	Phagocytosis
7. solvent drag	Transport of nutrients RBCs in blood

Diffusion

The process by which

-a gas or -a substance in solution -expands -because of the continuous random movements of particles -to fill all of the available volume

Net flux of

-solute particles
-from areas of high

To areas of low concentrations

Factors affecting diffusion

1. Fick’s Law of diffusion
Tendency to diffuse α A × Concentration gradient (magnitude)
2. Electrical charge of the ion
3. Distance

Time taken to reach Equilibrium α (diffusion distance) 2

4. Donnan effect
5. Membrane permeability

i. thickness of membrane (d) ii. lipid solubility iii. no. of protein channels per unit area

Types of diffusion

Non ionic diffusion

Net movement of undissociated substance

Donnan effect

Presence of a non diffusible ion

-on one side of a membrane-affects th -distribution -across that membrane

In a predictable manner.

Effects of Donnan’s phenomenon

1. Rupture of cells Normal cell volume & pressure depends on Na+ - K+ ATPase
2. inside of cell membrane is ( - ) charged
3. (plasma proteins) ion movement across the capillary wall

Active transport (uphill movement)

Energy required

	Іry Active	Пry Active
Energy Source	ATP (directly)	Derived from concentration gradients by 1ry Active transport
Eg:-	Na⁺K⁺ ATPase pump	Na⁺ /glucose transporter

Exocytosis & Endocytosis

Exocytosis

V – SNARE / t – SNARE proteins

↓ ↓ lock & key mechanism

On vesicle membrane

Ca⁺ dependent process

Endocytosis

Reverse of exocytosis

Types –

1. phagocytosis

Polymorphonuclear leukocytes engulf bacteria, dead tissue

2. pinocytosis

“cell drinking” - engulf substances in solution

Filtration

Movement of fluid due to difference in pressure on two sides

Amount of fluid filtered depends on
1. pressure difference on either side (∆P)
2. membrane permeability
3. surface area of membrane

Osmosis

Movement of solvent from a region of low solute [conc.] to a region of high solute [conc.] across a semi permeable membrane.

Osmotic pressure (op)

Pressure necessary to prevent migration by osmosis
Depends on no. of dissolved particles

Osmolarity - no. of osmoles per litre of solution Osmolality - no. of osmoles per kilogram of solvent
Plasma osmolality - 290 mosm/kg
Measured by - freezing point depression Calculated by -

BUN- Blood Urea Nitrogen ? Osmolarity measured increased ; calculated normal Why??
Osmolarity must have been increased due to a substance other than Na+, glucose, BUN

Tonicity

Osmolality of a solution relative to plasma
Isotonic - same as plasma Hypertonic - greater than plasma
Hypotonic - lesser than plasma

Interstitial fluid formation

Net Pressure = ↓( 37 – 1) – 25 mmHg ↑(1-17) + 25 mmHg

↓ 11 mmHg ↑9 mmHg

∆ P = ↓(11-9) mmHg

= ↓ 2 mmHg

Balance carried by lymphatics

Odema

Accumilation of interstitial fluid in bnormally large amounts.

Odema

Generalized	Localized
1. ↑ venous pressure in heart failure ↑ R atrial pressure. 2. hypoalbuminaemia + protein malnutrition +liver disease +nephritic syndrome	1. ↑ venous pressure in local obstruction 2. lymphatic obstruction -cancers -filariasis 3. ↑ capillary permeability -insect bites

Fluid and electrolyte balance

Factors affecting total body water

Why Infants & children more prone to dehydration

Distribution of electrolytes

Dilution principle

Movement of substances across biological barriersMechanism

Diffusion

Factors affecting diffusion

Donnan effect

Active transport (uphill movement)

Exocytosis & Endocytosis

Filtration

Osmosis

Osmotic pressure (op)

Tonicity

Interstitial fluid formation

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Movement of substances across biological barriers
Mechanism