1. Fluid, Electrolyte, and Acid Base Homeostasis
Chapter 27
Fluid, Electrolyte, and Acid Base Homeostasis

2. Fluid Compartments, Fluid Balance
Fluid separated by semi-permeable membranes into compartments
Four different compartments
Intracellular = inside cells
Extracellular = outside cells
Interstitial = between cells in the tissues
Plasma = fluid portion of blood

3. Fluid Compartments, Fluid Balance
Total Body Water (TBW) - 42L, 60% of body weight
Intracellular Fluid (ICF) - 28L, 67% of TBW
Extracellular Fluid (ECF) - 14L, 33% of TBW
Interstitial Fluid - 11L, 80% ECF
Plasma - 3L, 20% of ECF

4. Fluid Compartments, Fluid Balance
When in balance, required amount of water present and proportioned among various compartments according to their needs
Many things freely exchanged between fluid compartments, especially water
Fluid movements by:
bulk flow (i.e. blood circulations)
diffusion & osmosis - most I overall

5. Water General Largest single component of body, 45-75% of body
Fat is water free so more\less water in body depending on composition

6. Water Water balance Sources for 2500 ml - average daily intake
Metabolic Water
Preformed Water
Ingested Foods
Ingested Liquids
Balance achieved by output = 2500 ml
GI tract
Lungs
Skin
evaporation
perspiration
Kidneys

7. Regulating Fluid Intake - Thirst
Wetting mucosa of mouth (temporary)
Stretching of stomach
Decreased osmolarity of blood (most I)

8. Regulation of Fluid Output
Hormonal control
AntiDiuretic Hormone (ADH)
Aldosterone
Atrial Natriuretic Peptide (ANP)
Physiologic fluid imbalances
Dehydration:  blood pressure,  GFR
Overhydration:  blood pressure,  GFR
Hyperventilation - water loss through lungs
Vomiting & Diarrhea - excess water loss
Fever - heavy perspiration
Burns - initial fluid loss

9. Concentrations of Solutes
Non-electrolytes
molecules formed by covalent bonds
do not form ions in solution
Electrolytes
Molecules formed by ionic bonds
Disassociate into cations (+) & anions (-) in solutions (acids, bases, salts)
4 I functions in body
essential minerals
control osmosis of water
maintain acid-base balance
conduct electrical current

10. Distribution of Electrolytes

11. Electrolyte Balance Aldosterone Atrial Natriuretic Peptide
Female sex hormones (Estrogen, Progesterone)
Antidiuretic Hormone
Calcitonin
Parathyroid Hormone

12. Acid-Base Balance Normal metabolism produces H+ (acidity)
Three Homeostatic mechanisms:
Buffer systems - instantaneous; temporary
Exhalation of CO2 - operates within minutes; cannot completely correct
Kidney excretion - can completely correct any imbalance (eventually)
Buffer Systems
Consist of a weak acid and the salt of that acid which function as a weak base
Strong acids dissociate more rapidly and easily than weak acids

13. Acid-Base Balance Carbonic Acid - Bicarbonate Buffer Phosphate Buffer
A weak base
H+ + HCO3- ---> H2CO3 ----> H2O + CO2
Phosphate Buffer
NaOH NaH2PO > H2O + Na2HPO4
HCl + Na2HPO > NaCl + NaH2PO4
Protein Buffer
Most abundant buffer in body cells and plasma
Amino acids have amine group (proton acceptor, base) carboxyl group (proton donor, acid)

14. Acid-Base Imbalances Acidosis Alkalosis High blood [H+]
Low blood pH, <7.35
Alkalosis
Low blood [H+]
High blood pH, >7.45