1. Fluid, Electrolyte and pH Balance
Biology 2122
Chapter 26

2. Introduction – Body Fluids
1. Males (60%); Females (50%) Water
2. Fluid compartments
ICF vs ECF
Electrolytes
3. Fluid Movement
Moves through IF and plasma
Figure 26.3

3. Electrolyte Comparison
ECF vs. ICF
Figure 26.2

4. Water Intake and Output
2500 ml/day
2. Output
Insensible Water Loss
Osmolarity Changes
Thirst
ADH released from posterior pituitary
3. Hypothalamus – Thirst Center
Osmoreceptors – lose water
Figure 26.5
4. Sensible Water Loss

5. Thirst Mechanism

6. Water Balance Problems
1. Dehydration
Hypovolemic Shock
2. Hypotonic Hydration
Overhydration – ECF dilution
3. Hyponatremia
Low Na+ concentration; high water concentration
4. Edema
Interstitial space around tissue
Volume increase – IF only!
5. Hypoproteinemia

7. Electrolyte Balance – Importance of Sodium
1. Level – 142 mEq/L
Sodium bicarbonate and sodium chloride
2. ECF stability
3. Changes in plasma Na+ levels
Plasma volume; BP; ICF and IF
4. Regulation of Na+ balance
No specific sodium receptors
Aldosterone
Angiotensin II
ANP
Sex Hormones (Estrogen; progesterone; glucocorticoids)

8. Regulation of Sodium

9. Regulating Potassium 1. Main ICF ion 2. ECF balance 3. Buffer
4. Regulation
PCT (reabsorb 60-80%)
Loop of Henle (10-20%)
Collecting ducts (primary secretion)
5. Blood Plasma Concentration
Diets
6. Aldosterone
Enhances K+ secretion

10. Acid – Base Balance 1. Arterial Blood = 7.4 2. Alkalosis or Alkalemia
IF = 7.35
ICF = 7.0
2. Alkalosis or Alkalemia
3. Acidosis or acidemia
4. Where do the Hydrogen ions come from?
Protein catabolism; lactic acid; lipid metabolism; carbon dioxide transport
5. Regulation of pH
Chemical buffering; brain stem; kidneys

11. Bicarbonate Buffering System
(1). Only important buffer in the ECF
(2). Composed of:
Carbonic acid (H2CO3) and (NaHCO3) in solution – buffering substances
(3). Reaction
HCl + NaHCO  H2CO3 + NaCl
(SA) (WB) (WA) (SALT)
NaOH + H2CO  NaHCO3 + H2O
(SB) (WA) (WB)
(4). Alkaline reserve
Bicarbonate = 25 mE/L and carbonic acid = 1 mE/L

12. Phosphate Buffering System
(1). Components
Sodium hihydrogen phosphate and hydrogen phosphate ion
(2). Reactions
HCl + NaHPO  NaH2PO4 + NaCl
(SA) (WB) (WA) (Salt)
NaOH + NaH2PO  Na2HPO4 + H2O
(SB) (WA) (WB)
(3). Low concentrations phosphate – ECF
Blood plasma buffer – not as important; Important in urine and ICF

13. Respiratory Regulation [H+]
(1). General Characteristics
2x buffering power compared to chemical buffering systems
Slower
(2). During cell respiration – carbon dioxide and transport
CO2 + H2O  H2CO  H+ + HCO3 –
 
During carbon dioxide unloading: reaction shifts left and H+ produced from carbonic acid is reincorporated into water!

14. Renal Mechanisms
(1). Lungs can dispose of CO2 , chemical buffers do not dispose of excess acids and bases.
Acids generated by metabolism – metabolic ‘fixed’ acids
(2). Kidneys can eliminate excess acids and bases
(3). Renal mechanisms – regulating acid-base blood balance
Conservation- reabsorption of bicarbonate
Excretion of bicarbonate

15. Reabsorption of filtered bicarbonate – H+ secretion

16. New bicarbonate via excretion of H+ by HPO42-

17. Abnormalities 1. Respiratory Acidosis 2. Respiratory alkalosis
CO2 in blood; pH
2. Respiratory alkalosis
CO2; pH
3. Metabolic acidosis
HCO ; pH
4. Metabolic alkalosis