1. Water, Electrolyte, and pH Balance
It’s all a balancing act

2. Where do we keep our body fluids?
“Compartments”
Intracellular fluid
Inside the cells
2/3 of body fluid
Extracellular fluid
Interstitial fluid
Plasma
Intracellular fluid has an exacting composition
Plasma has an exacting composition
Interstitial fluid is the “slosh” compartment that lends to both as needed

3. Premises of Fluid and Electrolyte Regulation
Changes in extracellular fluid are monitored not intracellular fluid
Homeostatic response mechanisms are for the big picture not the individual cell
Fluid and electrolyte balance is not directly monitored, just hydrostatic and osmotic pressures
Water cannot be moved by active transport
Water can follow ions, remember the kidney
If gains exceed losses, you will gain water weight and visa versa

4. Regulatory Hormones Antidiuretic hormone Aldosterone
Produced by hypothalamus when it detects increase in osmolarity
Causes kidneys to concentrate urine
Stimulates thirst and desire for salty food
Aldosterone
Released by adrenal cortex when juxtaglomerular apparatus releases renin or when decreased levels of sodium and potassium are detected
Causes increased reabsorption of water

5. Regulatory Hormones cont.
Atrial naturitic peptide
Brain naturitic peptide
Both released when increase in blood pressure (stretch of right atrium or vessels in brain) is noted
Reduce thirst
Block ADH and aldosterone production

6. Fluid and electrolyte balance are linked
When water is up, electrolyte concentrations are down
When water is down, electrolyte concentrations are up

7. Water Movement Water moves freely into and out of the ECF compartment
Peritoneal cavity
Ventricles of brain
Gains
Metabolic generation of water
Absorption from digestive tract
Losses
Urine
Respiration
Feces
Sweat

8. Remember Hypertonic and Hypotonic?
When the ECF gaines water it becomes hypotonic to the ICF
Which direction will the water flow?
When the ECF loses water it becomes hypertonic to the ICF

9. Remember Hypertonic and Hypotonic? Cont.
What can happen to ECF then ICF volumes during dehydration?
What can happen to ECF then ICF volumes during over hydration?
What does this mean for the burn victim?
What does this mean for the dialysis patient?

10. Remember – Water follows sodium
Increase in sodium
Osmoreceptors stimulated
Increases ADH
Increase thirst
Decrease urine
Increase ECF
Dilution of sodium
Homeostasis restored
Decrease in sodium
Osmoreceptors inhibited
Decrease ADH
Decrease thirst
Increase urine production
Concentration of sodium
Homeostasis restored

11. Combined Water/Sodium Regulation
ECF increase
Inc blood volume
Atrial stretch
Release of atrial naturitic peptide
Decrease ADH, aldosterone, thirst
Decrease water intake, increase urination, increase sodium loss
Dec blood volume

12. Combined Water/Sodium Regulation cont.
ECF decreased
Dec blood volume/blood pressure
Inc renin, angiontensin
Inc aldosterone and ADH release
Inc thirst
Dec urine production
Inc sodium retention
Inc blood volume/blood pressure

13. Other Electrolytes Potassium Calcium Phosphate Kidneys regulate
When pH falls so does potassium secretion
When sodium retained potassium is secreted
Calcium
Calcitonin
Calcitriol (Vitamin D)
Parathyroid hormone
Phosphate
Calcitriol stimulates reabsorption along proximal convoluted tubule

14. Maintaining Proper pH What is an acid? What is a salt?
H+ donor
What is a salt?
An acid that has given up its H+ and taken up a metal ion
HCl  H+ + Cl-
Cl- + Na+  NaCl
What is a buffer?
A weak acid and its salt that give up or take up H+ as needed and prevent wild swings in pH

15. Maintaining Proper pH cont.
Types of acids
Volatile
Can come out of solution and enter atmosphere
Carbonic – H2CO3
Fixed
Stay in solution
Sulfuric and phosphoric
Organic
Participate in or produced by glucose metabolism
Acetyl-CoA
Lactic acid

16. Maintaining Proper pH cont.
Protein Buffer System C R OH O H N
If pH drops, extra H+ can bind here
If pH increases, H+ can leave here

17. Maintaining Proper pH cont.
Bicarbonate Buffer System
CO2 + H2O  H2CO3  H+ + HCO3-
H+ + HCO3- + NaCl  HCl + NaHCO3

18. Maintaining Proper pH cont.
Phosphate Buffer System
H3PO4-  H+ + HPO42-

19. Maintaining Proper pH cont.
Respiratory Compensation
When pH drops respiration increases
When pH rises respiration decreases
Renal compensation
Regulation of H+ and HCO3- secretion and reabsorption

20. Acid/Base Imbalance Disorders
Acidosis
Respiratory
Alveolar respiration can’t keep up
Metabolic
Too much lactic acid
Ketone bodies from alcoholism
Too much aspirin
Alkalosis
Hyperventilation
Rare – overuse of bicarbonates