01. Acid Base Physiology

Question 1

Respiration is stimulated by what?

Answer 1

1. Medullary Chemoreceptors- CSF pH (indirectly CO2)
2. Peripheral chemoreceptor- H+ ions.
3. Baroreceptors- response to hypotension, increases resp rate

Question 2

pH 7.0 = how many hydrogen ions

Answer 2

100 nmol/L

Question 3

Alkalosis effect on calcium ions?

Answer 3

Lowers free ionised concentration of calcium and encourages it to bind with proteins, can lead to tetany.

Question 4

Oxygen content value:

Coronary sinus

Answer 4

90mL/L

Question 5

Oxygen content radial artery?

Answer 5

200 mL/L

Question 6

Umbilical vein oxygen content?

Answer 6

130 mL/L

Question 7

Pulmonary artery oxygen content?

Answer 7

150 mL/L

Question 8

Living at altitude 5000m, what is the atmospheric pressure?

What would be paO2 after 7 days?

PaCO2 after 7 days?

Effect on oxygen dissociation curve?

Answer 8

At 5000m it would be half of atmospheric pressure.

PO2 lowered to 5-6 kPa.

PaCO2 would be lower.

Increase 2,3 DPG shifts curve to the right.
Bicarbonate excreted so will be low.

Question 9

Where in the kidney is the final urine pH determined?

Answer 9

DCT

Question 10

Phosphate is a buffer in which part of the cell?

Answer 10

Intracellular

Question 11

Affinity of oxygen to what protein is higher than its affinity for Hb?

Answer 11

Myoglobin

Question 12

What is myoglobin?

Answer 12

A single ferroprotein chain, can bind only one molecule of oxygen, releasing it at only extremely low PO2 levels.

Question 13

What is the normal P50 for Hb?

Answer 13

3.5 kPa

Question 14

Solubility of CO2 in plasma compared to O2?

Answer 14

CO2 is 25 times more soluble than O2z

Question 15

Carbon dioxide content of venous blood approx?

Answer 15

500 mL/ L

Question 16

Does the formation of carbamino compounds require an enzyme?

Answer 16

No, formation is rapid.

Question 17

What is the Haldane effect?

Effect of 2,3-DPG and breathing 100% O2 on Haldane Effect?

Answer 17

Describes that CO2 content in blood increases as Hb unloads O2, results mainly (70%) from the rapid formation of carbamino compounds by deoxyhaemoglobin.

This enhances unloading of CO2 in the lungs.

Not affected by 23-DPG or 100% oxygen inspiration.

Question 18

At peak exercise how much does:

1. Oxygen consumption increase?
2. Cardiac output increase?
3. Minute ventilation increase?
4. Oxygen extraction ratio increase?
5. Coronary oxygen extraction ratio??

Answer 18

1. Oxygen consumption increase?
   X 10
2. Cardiac output increase?
   X 5
3. Minute ventilation increase?
   X 10
4. Oxygen extraction ratio increase?
   X 2 = 0.5
5. Coronary oxygen extraction ratio??
   Does not increase as is already high, so just blood flow needs to increase.

Question 19

What percentage of oxygen is dissolved in plasma and what conditions can increase this?

Answer 19

1% dissolved in blood and can be increased by hyperbaric conditions.

Question 20

What causes left shift of oxygen dissociation curve?

Answer 20

Hypothermia 
Alkalosis 
Reduced 23-DPG 
Stored blood
Carbon monoxide, methaemoglobinaemia, fetal Hb

Question 21

Sodium drugs- acids or bases?

Answer 21

Acids

Question 22

Drug- sulphates: acids or bases?

Answer 22

Bases

Question 23

What is a normal anion gap?

Answer 23

8-16 mol/L

Question 24

What’s the normal amount of CO2 produced at rest?

Answer 24

200mL/L

With an RQ of 0.8

Question 25

What percentage Carboxylate-Hb present at rest?

Answer 25

0.5%

Question 26

What percentage of Hb is fetal Hb at rest in an adult?

Answer 26

0.5%

Question 27

Expected potassium levels and CO2 changes in 10 day history of pyloric stenosis?

Answer 27

Hypoventilation to compensate the metabolic alkalosis would increase PaCO2.

And metabolic compensation by retaining H+ renally by excreting K+ in exchange for H+ retention = hypokalaemia.