BODY FLUID COMPARTMENT

AND FLUID BALANCE

1

Body fluid compartment ECF also includes

lymph, CSF, synovial fluid, aqueous & vitreous humor,

endolymph & perilymph and fuild present in

pleural, pericardial and peritoneal cavities

2

The osmosis, diffusion, filtration and reabsoption provide for continual exchange of

water and solutes (electrolytes) among different body compartments

Yet, the volume of the fluid in different body compartments remains remarkably stable 3

Dynamics of capillary exchange (Starling’s Law of capillaries)

4

Concentration of

important solutes in ICF, ECF

5

Sources of body water gain and loss

Body fluid volume remains constant because water loss is equal to water gain 6

Sourse of metabolic water

Rate of formation of metabolic water is not regulated7

Regulation of body water gain

Rate of formation of

metabolicwater is not regulated to

maintain homeostasis

Water gain is regulated

mainly by drinking

through thirst

mechanism

2% decrease in body mass due

to fluid loss causes mild dehydration

Baroreceptor

8

Regulation of water and solute

loss This is

mainly done by the

kidneys 9

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10

One osmole is 1 gram molecular weight of undissociated solute.

Thus, 180 grams of glucose, which is 1 gram molecular weight of glucose, is equal to 1 osmole of glucose because

glucose does not dissociate.Therefore, 1 gram molecular weight of NaCl (58.5 gm) is

equal to 2 osmole because NaCl dissociates into Na+ and Cl- (and both are osmotically active).

A solution that has 1 osmole of solute dissolved in 1

Kilogram of water is said to have an Osmolality of 1 osmole per kilogram.

A solution that has 1 osmole of solute dissolved in 1 liter

(1000 ml) of water is said to have an Osmolarity of 1 osmole per liter.

Osmolality vs Osmolarity

11

Principle of OsmosisOsmosis is the net movement of water molecules

through a selectively permeable membrane

During osmosis water molecules pass through a selectively permeable membrane in two ways (1) through the lipid bilayer and (2) through

aquaporins (aqua = water) channels. 12

1. Is a measure of the total number of dissolved particles in a solution 2. Ionic composition of the ICF fluid is different from that of ECF

3. But Osmolarity of ICF is equal to that of ECF.

Osmolarity

13

ECF IS ISOTONICOsmotic equilibrium is maintained rapidly between ICF and ECF

Isotonic fluid gain: e.g Intravenous infusion of isotonic saline (0.9 % NaCl, 5% glcose solution) Isotonic fluid loss: Hemorrhage

No net fluid shift occur 14

ECF IS HYPERTONICWhat happens?

Water moves out of the cells to ECF until osmotic equilibrium is achieved Cells shrink as water leaves them

Neurons dehydration causes disturbances in brain function manifested as mental confusion to coma.

What Causes this?

Dehydration due to: Insufficient

water intake Excessive

water loss (vomiting or

diarrhea) Diabetes

Insipidus (deficiency of

ADH)

Accumulation of high levels of osmotically active solutes (urea in kidney

failure) 15

ECF IS HYPOTONICWhat happens?

Water moves into the cells from ECF until osmotic equilibrium is achieved. Pronounced swelling of neurons leads to brain dysfunction

Swelling of muscle leads to muscle weakness.Hypertension and edema caused by expansion of plasma volume.

What Causes this?Over hydration:

Renal failure with inability

to excrete diluted urine

Excessive drinking (transient)

Increase in ADH secretion

Water intoxication:

condition of over hydration,

hypotonicity and cellular swelling

from excess water. 16

Movement of water between body fluid compartments

17

Measurement of fluid volumes in the different body

compartmentsDye-dilution metod

(Indicator-dilution)

18

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