Respiratory Physiology - Acid Base Balance

Question 1

Acid definition

Answer 1

A molecule that releases hydrogen ions in solution

Question 2

Base definition

Answer 2

A molecule that can accept a hydrogen ion

Question 3

Buffer definition

Answer 3

A substance that can reversibly bind hydrogen ions

Question 4

Examples of buffers in the blood

Answer 4

Most important system is bicarbonate system, followed by protein then phosphate system least important of the three

Question 6

Equilibrium dissociation constant equation

Answer 6

K is dissociation constant at equilibrium

Solubility = 0.03 mmol/L/mmHg
Different units from previous solubility number for CO2

Question 7

Henderson-Hasselbalch equation

Answer 7

Rearranging and taking logs of equilibrium constant equation gives Henderson-Hasselbalch equation

Question 8

Henderson-Hasselbalch equation interpretation

Answer 8

If bicarb and PCO2 remain constant, pH remains constant

If Bicarb goes up, pH goes up

If PCO2 goes up, pH goes down

Question 9

pK value for bicarbonate system in normal physiology

Answer 9

6.1

Question 10

Diagram illustrating relationship between PCO2, bicarbonate and pH

Answer 10

Davenport diagram

Question 11

Buffer line for carbonic acid on Davenport diagram

Answer 11

Represents effects on carbonic acid (slash bicarbonate) in normal sample of blood when exposed to increasing / decreasing PCO2

Question 12

Effect on buffer line with increasing Hb

Answer 12

Steeper buffer line

More Hb gives more buffer to changes in PCO2

Question 13

4 types of acid base disturbances

Answer 13

Respiratory acidosis
Respiratory alkalosis
Metabolic acidosis
Metabolic alkalosis

Question 14

Why does bicarbonate increase with respiratory acidosis?

Answer 14

Move up the buffer line

Carbonic acid dissociates to H+ and HCO3-

Question 15

Effect of drop in pH as move

Answer 15

Move up the isopleth for the given PCO2 as kidney reabsorbs bicarbonate to improve pH and physiology associated

Question 16

Name for difference in bicarbonate from buffer line to give normal pH on isopleth line

Answer 16

Base excess!

Question 17

Metabolic acidosis with respiratory compensation in Davenport diagram

Answer 17

Question 18

Fick equation for diffusion through a sheet tissue

Answer 18

A = area
T = thickness
D = diffusion constant (different for different gases)

Sol = solubility
MW = molecular weight

CO2 has 20x higher diffusion through tissue barrier than O2 due to solubility

Question 19

Change in PO2 in tissue between capillaries

Answer 19

PO2 falls from capillary to the tissue as O2 is consumed

Also generates the PO2 gradient required for O2 diffusion

When PO2 in tissue drops to zero, produces ATP via anaerobic respiration

Question 20

Why is PO2 so much higher than PO2 in tissue

Answer 20

To generate PO2 gradient for O2 diffusion into tissue

Question 21

Approximate PO2 in muscle

Answer 21

2 to 5 mmHg

Question 22

Classification of tissue hypoxia

Answer 22

Hypoxic hypoxia
Anaemic hypoxia
Circulatory hypoxia
Histotoxic hypoxia

Question 23

Examples of hypoxic hypoxia

Answer 23

High altitude
Respiratory failure

Question 24

Circulatory hypoxia

Answer 24

Reduced perfusion due to shock and subsequent reduced perfusion

Question 25

Histotoxic hypoxia

Answer 25

Poison in tissue which prevents tissue from utilising O2

Eg cyanide poisoning - interferes with mitochondrial mechanism