Acid-base balance

Question 1

How does the respiratory system produce acid?

Answer 1

Carbonic acid from CO2

Question 2

How is acid produced metabolically?

Answer 2

Organic acid (lactic, amino, hydroxybutyric) and inorganic (sulphuric, phosphoric)

Question 3

How does the respiratory system remove acid?

Answer 3

Ventilation removes CO2

Question 4

How is acid removed metabolically?

Answer 4

Inorganic acids (excreted by kidneys unchanged) and organic acids (undergo liver metabolism)

Question 5

pH

Answer 5

• pH = -log10[H+]
• Acid-base homeostasis aims to keep pH constant
• Buffers act immediately
• Respiratory acts rapidly (minutes to hours) - normally self-regulated
• Renal is slow (hours to days)

Question 6

pH buffers

Answer 6

• Proteins: albumins (ECF) and haemoglobin (ICF)
• Phosphate (ICF): HPO42- + H+ < = > H2PO4-
• Carbonic acid/bicarbonate system in ECF

Question 7

What is the main ECF buffer?

Answer 7

Carbonic acid/bicarbonate

Question 8

Henderson-Hasselbalch equation

Answer 8

pH = pKa + Log (HCO3- / H2CO3)

Question 9

Equation for carbonic acid/bicarbonate buffer

Answer 9

H2O + CO2 = H2CO3 = H+ + HCO3-

Question 10

What does PCO2 represent?

Answer 10

Respiratory component of acid-base balance

Question 11

How does the renal buffer change pH

Answer 11

Alters H+ absorption

Question 12

Function of intercalated cells

Answer 12

Determine final urine acidity in DCT

Question 13

What is acidosis?

Answer 13

Impaired acid excretion

Question 14

How is sodium reabsorbed?

Answer 14

H2CO3 dissociates to form H+ ions
Na+/H+ anti porter moved H+ out of tubular cell and Na+ in
Co-transport mechanism moves Na+ and HCO3- into interstitial fluid

Question 15

+ve BE

Answer 15

Metabolic alkalosis

Question 16

-ve BE

Answer 16

Metabolic acidosis (base deficit)

Question 17

Anion gap

Answer 17

• Identify cause of metabolic acidosis as being disturbance of organic (raised anion gap) and inorganic acids (normal anion gap)
• Total cations must = anions
• Difference between cations and anions is mainly albumin

Question 18

Acid-base compensation

Answer 18

• If one system fails, the other compensates
• Speed depends on system involved
• Respiratory = rapid
• Metabolic = slow
• Moves pH towards normal but never to normal if underlying disease still present
• Respiratory compensation: increased H+ acts on peripheral chemoreceptors to increase Vmin → H+ in blood can’t cross BBB
• Metabolic compensation: increased CO2 means more HCO3- retained

Question 19

Indicator of metabolic acidosis

Answer 19

Decreased HCO3-

Question 20

Indicator of respiratory acidosis

Answer 20

Increased CO2

Question 21

Indicator of respiratory alkalosis

Answer 21

Decreased CO2

Question 22

Indicator of metabolic alkalosis

Answer 22

Increased HCO3-