Fluid, Electrolyte and Acid-Base Dynamics

Human Anatomy and Physiology IIOklahoma City Community College

Dennis Anderson

Concentration of Solutions

• Percent Salt– 0.9% NaCl

• Milliosmoles– 300 milliosmoles/Liter

• Milliequivalents– 325

milliequivalents/Liter

Osmosis

Osmosis

Hypertonic Solution

0.9% NaCl

3% NaCl

Cells Crenate in a Hypertonic Solution

Hypotonic Solution

0.9% NaCl

0.5% NaCl

Cells in a Hypotonic Solution Swell and May Lyse

Isotonic Solution

0.9% NaCl

0.9% NaCl

310 mosm

300 mosm

Which Way Will Fluid Move?

Application Problem 1

•Michael has recently started working outdoors in the hot weather to earn money for his tuition. After a few days he experienced headaches, low blood pressure and a rapid heart rate. His blood sodium was down to 125 meq/L. The normal is 144 meq/L. How do you explain this?

Answer to Problem 1

• Michael lost sodium by perspiration. The low sodium in his blood allowed fluid to move into cells by osmosis. Lack of fluid lowered his blood pressure to give him a headache. The increased heart rate was his bodies way of trying to increase blood pressure.

Application Problem 2

•Frank has hypertension. His doctor has advised Frank eat a low salt diet. Frank consumed a lot of salt the day before his last checkup. His blood pressure was up. Why?

Answer to Problem 2

• The extra salt Frank ate made his blood hypertonic. Hypertonic blood will attract fluids from body cells by osmosis.

Electrolyte vrs. Nonelectrolyte

NaCl Na+ + Cl-

Glucose Glucose

Carbon Dioxide and Acid

CO2 + H2O H2CO3 H+ + HCO3-

Carbonic Acid

More Carbon Dioxide = More Acid = Lower pH

• Breathing slower will retain CO2 , pH will– decrease (more acid)

• Breathing faster will eliminate more CO2 pH will– increase (less acid)

Blood pH Drops to 7.3How does the body compensate?

• Breath faster to get rid of carbon dioxide– eliminates acid

Blood pH Increases to 7.45How does the body compensate?

• Breath slower to retain more carbon dioxide– retains more acid

John is Taking Narcotics for PainThe narcotics have depressed his breathing rate. What will happen

to his blood pH?• pH will decrease

because he will retain excess carbon dioxide which will increase the amount of acid in the blood

Buffers Regulate pH

• Chemicals that resist changes in pH• Prevent large pH changes when an acid or

base is added

Strong Acid• Acid that releases many hydrogen ions• HCl

Weak Acid• Acid that releases only a few hydrogen ions• Carbonic Acid

Buffers Change Strong Acids to Weak Acids

HCl + NaOHStrong Acid

BaseH2CO3+ NaClWeak Acid Salt

Acidosis• pH below 7.35• Depresses the nervous system

– coma

Alkalosis• pH above 7.45• Overexcites the nervous system

– convulsions