Acid-Base Balance

What is the largest source of potential acids in the body

CO2

Volatile acid

acid that can be partially converted into a gas at atmospheric pressure

What reaction does Carbonic anhydrase catalyze

Between CO2 and H2O to form H2CO3

What type of acids do lungs make

volatile acids

Carbon buffer system

CO2 + H2O → H2CO3 H+ → + HCO3-

What type of acid does metabolism generate

nonvolatile acids

What type of acid do kidneys excrete

Kidneys excrete nonvolatile acids

What is the acid production per day

net acid production per day

Henderson-Hasselback equation for bicarbonate buffer

pH = [HCO3-]/PaCO2

Normal range of PaCO2

35-45 mmHg (40 mmHg)

Normal range of plasma [HCO3-]

22-26 mmol/L or mEq/L

Chemical reactions that produce CO2

Oxidation of neutral carbohydrates + fat

Oxidation of most neutral amino acids

Chemical reactions that produce nonvolatile acids

Don’t generate CO2

• Oxidation of sulfur-containing aa’s

• Oxidation of phosphorous-containing compounds

• Production of nonmetabolizable organic acids

• Incomplete oxidation of carbohydrate and fat

What is the major buffer system of the ECF

bicarbonate buffer system

Major buffer systems of the renal tubular fluid

Filtered Bicarbonate-

• 99% of filtered bicarbonate is reabsorbed (not technically because its actually the release of new bicarbonate)

• Filtered phosphates

• Ammonium

Filtered phosphates buffer system equation

HPO4 2- + H + → H2 PO4

How filtered phosphate buffer system works

• Secreted H+ combines in the tubular lumen with phosphate ions

• New bicarbonate is contributed to the blood

How ammonium buffer system works

• Renal metabolism of glutamine generates ammonium ions that contain H+

• New bicarbonate is contributed to the blood

Normal pH range of arterial blood

7.35-7.45

Why is venous blood pH lower than arterial pH

more CO2 in venous blood than arterial blood

Body buffer system- proteins

fast, immediate response (e.g. hemoglobin bind to CO2 and H+)

Body buffer system- bone minerals

key defense mechanism in chronic situations of acidosis, but compromises bone quality

Respiratory regulation

Fast response system that regulates the elimination of volatile acids

What happens to ECF pH when alveolar ventilation decreases

When alveolar ventilation is decreased, more CO2 is retained in the arterial blood, decreasing plasma pH

What happens to ECF pH when alveolar ventilation increases

When alveolar ventilation is increased, more CO2 is expired, increasing in plasma pH

What happens to alveolar ventilation with low plasma/ECF pH

When plasma H+ concentration is elevated (aka low pH), peripheral and central chemoreceptors send signals to increase ventilation

What happens to alveolar ventilation with high plasma/ECF pH

When plasma H+ concentration is decreased (aka high pH), peripheral and central chemoreceptors send signals to reduce ventilation

Proximal tubule and ascending limb of loop of Henle involvement in renal regulation of acid-base balance

Reabsorb HCO3 - and secrete H+

Principal cells in collection tubule involvement in renal regulation of acid-base balance

reabsorb Na+ and Cl-, secrete K+

intercalated cells in collection tubule involvement in renal regulation of acid-base balance

A/alpha cells: secrete H+

B/beta cells: secrete HCO3-

pH effects on kidney secretion/absorbtion of Bicarbonate

high pH- more secretion of bicarbonate

low pH- more absorption of bicarbonate

Primary disturbance for respiratory acid-base disorders

PaCO2

Primary disturbance for metabolic acid-base disorder

HCO3-

Respiratory acidosis primary disturbance and compensation

disturbance: increased PaCO2

compensation: net absorption of HCO3- (increase)

Respiratory alkalosis primary disturbance and compensation

disturbance: decreased PaCO2

compensation: excretion of HCO3- (decrease)

Metabolic acidosis primary disturbance and compensation

disturbance: decreased HCO3-

compensation: increase ventilation to eliminate more CO2

Metabolic alkalosis primary disturbance and compensation

disturbance: increased HCO3-

compensation: decrease ventilation to retain more CO2