ACID-BASE BALANCE

• pH is a measure of H +

• pH = - log [H +]

• Importance:– Chemical reactions

Acid + Base = Salt Water(NEUTRALIZATION REACTION: HCl + NaOH NaCl + H2O)

pH SCALE

• Logarithmic• 1.0 to 14.0• 7.0 = neutral (chemical)• 7.4 = normal (biological)• <7.0 (7.4) = acidic• >7.0 (7.4) = alkaline (basic)• body pH range = 7.35 to 7.45

ACIDS AND BASES

• Acid = releases H+ = proton donor

• Base = accepts H+ = proton acceptor

• Strong acid vs. weak acid

• Strong base vs. weak base

SOURCES OF H+

• Metabolic reactions• Carbon dioxide• Exercise acids• Food

pH MAINTENANCE

• Buffer systems

• Respiratory system

• Urinary system

BUFFER SYSTEMS• Buffer = substance preventing extreme

fluctuations of pH• Strong acids/bases to weak ones• Work in buffer pairs; a base and an acid• Action:– BB + strong acid weak acid + salt– BA + strong base weak base + water

• Systems: bicarbonate; phosphate; protein

BICARBONATE BUFFERS

• Important in blood• Buffer pair = NaHCO3/H2CO3

• HCl + NaHCO3 H2CO3 + NaCl

• NaOH + H2CO3 NaHCO3 + H2O

PHOSPHATE BUFFERS

• Important in kidney• Buffer pair = Na2HPO4/NaH2PO4

• HCl + Na2HPO4 NaH2PO4 + NaCl

• NaOH + NaH2PO4 Na2HPO4 + H2O

PROTEIN BUFFERS• Important in cells• Amphoteric• Side groups:– COOH acts as acid – donates H+

– NH2 acts as base – accepts H +

• Hb can act as a buffer

Respiratory Control of pH• Review respiratory centers of brain • Review respiratory equation• Review chemoreceptors• It is fast acting when buffers need help• Control lasts relatively short time• NOT a long term solution• H+ = pH = resp. equation left = ventilation• Consider the opposite scenario

Renal Control of pH• Kidney slow to respond to pH changes• Responds only after persistent changes• Compensates for a relatively long period• NOT a solution to chronic pH problems• Rids the body of H+ by tubular secretion– PCT, DCT, CD

• Also:– Reabsorption of HCO3

-

– Regulation of PO4 -3

– Production and elimination of NH3

Summary of Kidney Action

Blood Tubule Cells Filtrate CO2 CO2+ H2O

H2CO3-

HCO3- + H + H + + Na2HPO4

Na+ + NaH2PO4Na+Na+

HCO3-

+

NH3 H+NH3 +

NH4+

(for excess H+)

Coupling of H+ Secretion &Reabsorption of HCO3

-

p. 1007

Buffers & New HCO3-

p. 1008

New HCO3- & Ammonia

p. 1009

Acidosis & Alkalosis

• Look at the listed values in the above order

Range Acidosis Alkalosis

pH 7.35-7.45 < 7.4 > 7.4

pCO235-45 mmHg > 45 mmHg < 35 mmHg

HCO3- 22-28 mEq/L < 22 mEq/L > 28 mEq/L

Acidosis & AlkalosisAcidosis Alkalosis

Respiratory •Respiratory problems

•Rapid, shallow breathing

•Overdose

•Brain stem injury

•Hyperventilation

•Brain stem injury

Metabolic •Diarrhea

•Renal disease

•Starvation

•Excess alcohol

•Increased ECF

•Vomiting

•Excess diuretics

•Excess bicarbonate

•Constipation

•Excess aldosterone

Compensation

• One system helping another to alleviate an acid/base problem:– An overload of the buffer system results in an

increase in breathing rate; the respiratory system is compensating.

Fluids & Electrolytes• Body water content

• Fluid compartments:– Intracellular– Extracellular• Plasma• Interstitial fluid

Fluid Compartments

p. 1041

Fluid Composition

• Electrolytes

• Nonelectrolytes

• Comparison of intracellular & extracellular

Fluid Composition

p. 1043

1. Note sodium and potassium

2. Note similarity of plasma & interstitial fluid except for protein

Fluid Movement

• Water follows osmotic and hydrostatic pressure gradients

Intracellular Interstitial Plasma

Fluid & Solute Movement

p. 1037

Water Balance• Input must equal output

p. 1037

Regulation of Water Intake

p. 1038

Disorders of Water Balance

• Dehydration– Water loss exceeds intake; When?– Diabetes– Decreased volume = hypovolemic shock– Water movement out of cells

• Hypotonic hydration (Water intoxication)– Excess water– Diluted ECF– hyponatremia

• Edema

Disorders of Water Balance

p. 1040

Electrolyte Regulation - Sodium

p. 1043

ADH Action

p. 1039

Water: Pressure /Volume Relationships

p. 1039

Water: Pressure /Volume Relationships

p. 1045

Respiratory Centers

• Medulla• Pons– Apneustic – works to smooth transition between

inspiration and expiration– Pneumotaxic (pontine respiratory group) • Inhibits respiratory center• fine tunes rhythm• Prevents overinflation

END