This document discusses concepts related to body fluid balance including osmolarity, osmosis, tonicity, fluid exchange across capillaries, edema, and water balance. It defines key terms and describes the normal processes that regulate fluid balance as well as potential abnormalities that can disrupt balance and cause edema. Factors that influence fluid filtration, absorption and the forces that govern fluid movement between compartments are explained.

1. ‫الرحيم‬ ‫الرحمن‬ ‫هللا‬ ‫بسم‬
body fluids

2. OSMOALRITY
 Is the number of osmoles of solute per one
liter of solution.
 Used to describe the concentration of
osmotically active particles in a solution.
 If a solute dissociate into ions to form an ideal
solution, each liberated ion is an osmotically
active particle.
 The osmotically active particles can exert
osmotic pressure if they are in contact with
another solution but separated from it by
semipermeable membrane.

3. Osmosis
 Movement of water molecule across the a
semipermeable membrane from a region of
low con.c of solute to a region of high
concentration of solute.
 All cell membranes and capillaries are
semipermeable membranes.
 Osmotic pressure is the pressure to prevent
osmosis.

4.  Osmolarity of the plasma = 280-300 mosm/l
 Na+ & its anions are responsible for most of
this osmolarity.
 Osmolarity of the ICF = 280-300 mosm/l
 K+ & its anions are responsible for most of
this osmolarity.

5. tonicity
 Used when describing the osmolarity of a
solution relative to the osmolarity of the
plasma.
 So that there are 3 types of solution:
 Isotonic : with osmolarity similar to plasma.
 Hypotonic : with osmolarity lower than
plasma.
 Hypertonic: with osmolarity higher than
plasma.

6. Effect of different types of
solutions on cells

7. Fluid exchange
 Fluid exchange between ICF & ECF occur by
osmosis.
 Whereas between plasma & interstitium occur
by starlings forces.

8. Solute and Fluid Exchange Across
Capillaries

10.  There are 4 primary forces that control
fluid exchange at the capillaries which
include:
 1. Capillary hydrostatic pressure:
 Pressure acting on the lateral wall of the blood
vessel.
 For filtration (from plasma to ISF)
 35 mmHg at the arteriolar end of capillaries.
 15 mmHg at the veniolar end of capillaries.

11. CON
 2. Capillary oncotic pressure:
 Is the osmotic pressure of the plasma proteins.
 Exerted mainly by albumin.
 For absorption (from ISF to plasma).
 25mmHg through out the capillaries because
the proteins are not filtered

12. con
 The interstitial fluid hydrostatic & oncotic
pressures are of low magnitude, they cancel
each other and they are negligible.
 The net pressure (HP-OP):
 At the arteriolar end = 35-25 = +10mmHg
(filtration).
 At the veniolar end= 15-25 = -10 (absorption)

13. FORCES OF FLUID EXCHANGE

14. con
 Plasma is filtered at the arteriolar end to the
inerstitum carrying nutrient to the surrounding
cells & then absorbed back at the veniolar end
carrying waste products.
 90% of fluid filtered is absorbed at the
veniolar end the remaining 10% is absorbed
by the lymphatic vessels.
 Disturbance of this balance result in
accumulation of fluid interstitium causing
edema.

16. Edema
 Abnormal accumulation of fluid in the
interstitial space.
Mechanisms:
 ↑ capillary HP:
 CAUSED BY :
 Heart failure, result in generalized edema
 Venous obstruction, result in localized edema

17. con
 ↓ oncotic pressure :
 CAUSED BY :
 Malnutrition, result in generalized edema.
 Malabsorption , result in generalized edema.
 Chronic liver disease, result in generalized
edema

18. Con
 Lmyphatic obstruction:
 CAUSED BY:
 Filaria worms, result in localized edema
(elephantiasis).
 Surgical removal of lymph nodes, result in
localized edema.

19. con
 ↑ permeability of capillaries:
 CAUSED BY :
 Inflammation, result in localized edema.
 Burns, result in localized edema.
 Allergy: involves release of histamine which ↑
permeability & result in generalized or
localized edema.

20. Types of edema
 Pitting edema :
 In which firm pressure by the thumb leaves a
mark on the skin.
 Non pitting edema:
 In which firm pressure by the thumb does not
leaves a mark on the skin.

21. Water balance
 To maintain constant water content of the
body, water loss should always = water intake
 Abnormalities of this balance between water
intake & output can cause disturbances in
volume & osmolarity of body fluid
compartment.

22. Water balance
 Input = output
normal daily water intake :
 Drinking 1.3L/day
 Solid Food 0.9L/day
 Metabolism 0.3L/day
The average water intake is about 2.5L/day
normal daily water output:
 Urine 1.5 L/day
 Stool 0.1L/day
 Sweat &Insensible perspiration (skin ,lung)
0.9L/day the average water loss is about
2.5L/day

23. Con
 The above values vary greatly in different
physiological & pathological conditions.
 Examples of physiological conditions:
 Type of work: heavy work ↑ sweating.
 Exercise: strenuous exercise ↑ sweating &
causes hyperventilation which ↑ insensible
water loss in expired air.
 Degree of water intake: high intake ↑ the urine
volume and vice versa.
 Variation in body temperature & environmental
temperature.

24. Con
 Examples of pathological conditions:
 Abnormal water intake through:
 ↑ metabolism (fever & hyperthyroidism).
 ↑ drinking (psychologic polydypsia).
 Excess intravenous fluids (fluid overload)
 Abnormal water loss through:
 diarrhea.
 Polyuria (diabetes mellitus).
 Excessive sweating (heat exhaustion).