1. Renal regulation of body fluid
Dr. Eman El Eter

2. What happens when you are exposed to hot weather?
What is the impact of the following on your body fluid volume and osmolarity?
What happens when you are exposed to hot weather?
What if you have a stomach bug and excessive diarrhea?
What if you drink 2 liters of fluids?

4. ECF Constant concentration of electrolytes & solutes
They create the osmolarity of ECF
Na+, Cl- most abundant osmostic molecules.
Osmolality is determined by the amount of extracellular NaCl and water which depends upon balance between intake and excretion of these substances.
Normal plasma Na+ = mEq/L
Osmolarity = 300 mOsm/L

5. To stay in a state of fluid balance:
Input = output
Input= 1500 ml/day
H2O & fluid consumption
Output = 1500 ml/day
Urine
Respiration (water vapor)
Sweating.
Stool
Metabolism

6. Control of ECF volume &osmolarity
Regulation of input:
Osmoreceptors/Thirst mechanism
Regulation of output: Renal regulation
ADH.
Angiotensin/Aldosterone.

7. Thirst mechanism

8. Role of thirst in controlling ECF osmolarity & fluid volume
To stay in balance water intake = water loss
Fluid intake is regulated by thirst mechanism
Stimuli of thirst mechanism:
A. Increase thirst:
Increased osmolarity ECF.
Decreased ECF volume.
Decreased blood pressure.
Angiotensin II.
Dryness of the mouth.
B. Decrease thirst?
Gastric distention decreases thirst.

9. The desire to thirst is completely satisfied when: Plasma osmolarity,
Role of thirst in controlling ECF osmolarity & Na+ concentration, cont….
The desire to thirst is completely satisfied when:
Plasma osmolarity,
Blood volume,
Or both return to normal

10. Osmoreceptor mechanism
Changes in plasma osmolarity can lead to a cascade of events to return it back to normal.

11. What happens if ECF osmolarity increased?
(+) osmoreceptors in
Ant. Hypothalamus &
Send signals to
Supraoptic nucleus,
Then to posterior
Pituitary (+) ADH
To increase H2O absorption

12. Where in the brain ADH is formed?
Main site for ADH synthesis
ADH is stored in posterior pituitary

13. Osmotic vs non-osmotic stimuli; effect on ADH
Rapid response
AVP=arginine vasopressin=ADH

14. Summary of actions & stimuli of ADH

15. Non-osmotic stimuli releasing ADH
Arterial baroreceptor reflex
Chemoreceptor reflex
Whenever BP & blood volume reduced, ADH is released water retention by the kidney to restore BP to normal.
Day-to-day regulation of ADH secretion is effected mainly by changes in plasma osmolarity.

16. Role of Ang II & aldosterone
They do not normally play a major role in controlling ECF osmolarity and Na+ concentration.
Their major role is to absorb sodium through distal convoluted tubules, leading to greater extracellular fluid volume and sodium quantity.

17. Take home message
ADH-thirst is the most powerful feedback system in the body for controlling extracellular fluid osmolarity and volume.