Lecture 8: Acid-base Balance #1

Question 1

What is pH and why is it so tightly regulated?

Answer 1

Measure of [H⁺] in solution.

Tightly regulated so the proteins/moleules can function.

Question 2

Acidosis (acidemia) and Alkalosis (alkalemia) ranges

**Acidosis and alkalosis are processes that cause abnormal pH

Answer 2

pH 7.4 = normal (7.35-7.45)

if pH <7.35 = acidosis
<7.2 = severe acidosis
<6.9 = incompatible with life

If pH >7.45 = alkalosis
>7.6 = severe alkalosis
>7.9 = incompatible with life

Question 3

Purpose of a Buffer? Equation

Answer 3

A weak acid/base solution that minimises pH change due to +/- of H⁺

Only removes H+ temporarily

pH = pK + log ([base] / [acid])

Question 4

pK of a buffer is?

Answer 4

pH at which the concentrations of A- (base) and HA (buffer) are equal

Question 5

What are the 2 main buffers in blood?

Answer 5

1. Bicarbonate
   * H⁺ (40nmol/L) + HCO₃^- (24mmol/L) ⇔ H₂0 + CO₂*_{<u>​​</u>}
2. Proteins: albumi, haemoglobin
   * *H+ + A- ⇔ HA**

Question 6

Why do we have so much H+ to remove?

Answer 6

Body metabolism produces large amounts of CO2 every day (>1500mmol/day), that drives

Question 7

REspiratory control over pCO2?

Answer 7

• Increased pCO2 → acidosis*
• decreased pCO2 → alkalosis*

Increased pCO2 → acidosis/ low pH → stimulated increase in ventilation → more expired CO2

Question 8

What does a blood gas analyser measure?

Answer 8

pH, pO2, pCO2

bicarbonate and base excess

Question 9

Types of Respiratory Disturbances

Answer 9

CO2 retention (eg; acute asthma) → respiratory acidosis
Low pH and High pCO_²

CO2 Expiration (eg; hyperventilation) → Respiratory alkalosis
High pH and low CO₂

Question 10

Types of Metabolic Disturbances

Answer 10

Metabolic Acidosis: Low pH and low HCO3-

Increased acid production → leads to a low HCO₃^- as the buffer has been ‘used up’ → eventually renal buffers can also be used up.

Metabolic Alkalosis: High pH and high HCO₃^-

Either due to an increase of HCO₃^- injestion or Loss of acid (vomiting)

Question 11

Main causes of Metabolic Acidosis (low pH and HCO3-)

Answer 11

1. Increased Acid Production
   * *- Lactic Acidosis:** hypoxia, poor tissue perfusion (car accident, MI)
   * *- Diabetic Ketoacidosis (DKA):** increased betahydroxybutyric acids
2. Decreased Acid Excretion
   * *-Renal Failure
   - Renal Tubular Acidosis**

Question 12

Role of Kidney Buffers in acid-base balance?

Answer 12

Can excrete H+ via Renal buffers (just like bicarbonate). These are generally PO₄^3- and NH₃

Maintain urinary pH between 5-8

Question 13

List a few rarer causes of metabolic acidosis

Answer 13

Methanol and ethylene glycol poisoning

Glue/paint sniffing

Alcoholic Ketoacidosis

Question 14

What is Respiratory compensation in metabolic acidosis

Answer 14

Normally M. acidosis is a low pH and low HCO3- .
This low pH stimulates ventilation, “acidotic breathing”, lowering pCO2 and balancing the low bicarbonate change.

Question 15

3 Roles of Kidney in Acid-base balance?

Answer 15

1. Bicarbonate Reabsorbtion (Proximal Tub.)
2. New Bicarbonate Generation (Proximal Tub., via carbonic Anhydrase)
3. H+ secretion (distal Tubule)

Question 16

1. Proximal Tubule: Bicarbonate Reabsorbtion

Answer 16

Filtered HCO3- is reabsorbed across BL membrane similar to Na+

Question 17

2. Proximal Tubule: New Bicarbonate generation

Answer 17

Acetazolamide= carbonic anhydrase inhibitor that causes metabolic acidosis.

Hypervent. → resp. alkalosis →(acetazolamide) → decreased Carbonic anhydrase activity → decreased HCO3- generation→ metabolic acidosis

Question 18

3. H+ excretion in the distal Tubule

Answer 18

ENaC (Na+ epithelial channel) creates a difference across the membrane by driving Na+ reabsorbtion. THis drives K+ and H+ into the distal lumen for excretion

Question 19

how does renal Compensation counteract Resp. acidosis

Answer 19

By increasing HCO₃^- generation in the proximal tubule, restoring the ratio.