Central chemoreceptors

Question 1

What is the main activator of the central chemoreceptors

Answer 1

Hypercapnia - Increased CO2 levels

Question 2

Where are the central chemoreceptors found

Answer 2

Brain parenchyma

In the bathed extracellular fluid - separated from the blood by the blood brain barrier

Question 3

What pCO2 is required in order to double ventilation

Answer 3

40-45mmHg

Question 4

What happens if arterial pCO2 increases?

Answer 4

Brain exctracellular fluid pCO2 increases - causes a pH fall and stimulation of the central chemoreceptors

Question 5

Why is a larger fall in pH seen in the blood vessel

Answer 5

Poor ion permeability - less non-bicarb buffering power (fewer proteins) so larger fall

Question 6

What 2 neuronal populations are found on the ventrolateral medulla and other brainstem nuclei

Answer 6

Acid activated - serotonin

Acid inhibited - GABA

Question 7

What responses are seen as a result of respiratory acidosis

Answer 7

Both peripheral and central chemoreceptor action

Peripheral is faster, As pO2 falls the response to pCO2 is enhanced

Question 8

What response is seen as a result of metabolic acidosis

Answer 8

Severe response - hyperventilating (Kussmaul breathing)
Large reduction in pCO2 - peripheral acute response (short term)
Central - longer term role

Question 9

What are the renal mechanisms of action

Answer 9

Long term regulation
3 mechanisms - HCO3 handling
Urine acidification
Ammonia synthesis

Question 10

Where does HCO3 handling take place

Answer 10

90% in the proximal tubule

10% in the distal tubule

Question 11

How does HCO3- get reabsorbed at the proximal cell

Answer 11

Binds to H+ secreted by the Na/H to form H2CO3 - carbonic anhydrase to form CO2 and H2O - enters the cell - intracellular carbonic anhydrase to remake H2CO3 - Dissociates into HCO3- reabsorbed and H+ is recycled

Question 12

How is urine acidification achieved

Answer 12

Filtered Na2HPO4 loses a Na ion to the Na/H exchanger

Gains an H from the exchanger to form NaH2PO4

Question 13

Why is ammonia production important in urine acidification

Answer 13

Ammonia produced in Krebs cycle - Glutamine - alpha keto-glutarate
Gains an H+ and becomes impermeable to the cell membrane so stays in the renal fluid and is excreted in urine

Question 14

What is the renal compensation for respiratory acidosis CO2 elimination is low (lung disease)

Answer 14

Secretion of H+ increased
Increased reabsorption of HCO3-
Rise in pH but further rise in HCO3-

Question 15

What is the renal compensation for respiratory alkalosis (Increased CO2 elimination) - Hyperventilating

Answer 15

Reduced secretion of H+
Reduced reabsorption of HCO3-
Fall in pH but further drop in HCO3-

Question 16

What respiratory compensation is there for metabolic acidosis (Ingestion of acid, Loss of alkaline, Diarrhoea)

Answer 16

Increase respiratory rate
Reduced arterial pCO2
increased pH and drop in pCO2
Renal correction too: Increased secretion of H+, Increased reabsorption of HCO3-

Question 17

What is the respiratory compensation of metabolic alkalosis (loss of acid/vomiting)

Answer 17

Reduced respiratory rate
Increased arterial pCO2
Reduced pH and rise in pCO2

Question 18

What is an additive mixed dissorder

Answer 18

Both same type of pH change - Life threatening

Question 19

Give three mixed disorder examples

Answer 19

1. Alcoholics - met acidosis (alc breakdown) met alkalosis (Vomiting)
2. Asthma - resp acidosis and lactic acidosis due to lack of O2
3. COPD patients treated with diuretics - resp acidosis and met alkalosis