Respiratory acid-base

Question 1

What are the global systems regulating acid-base?

Answer 1

1. Chemical buffering in extracellular fluid
2. Respiratory response - depth and rate
3. Renal - excretion of H+, Re-absorption and re-generation of HCO3-
4. Intracellular buffering (HCO3-, PO4- and proteins)

Question 2

What is the effect of a drop in pH on the dissociation of haemoglobin and oxygen?

Answer 2

A drop in pH (rise is H+ ions) leads to a reduced capacity for oxygen on the haemoglobin molecule. Haemoglobin will bind H+ in preference to O2 at higher H+.

Question 3

How can you use the concentration of HCO3- and CO2 to determine whether an acidosis is respiratory or metabolic?

Answer 3

According to the Hendersen-Hasselbach equation for HCO3- and CO2, if a drop in pH is metabolic, HCO3- will be low. For a respiratory cause, CO2 will be raised.

Question 4

How is the bicarbonate system “open”?

Answer 4

the system is open because the reactants and products are replenished or removed:

1. Metabolism continues to produce CO2
2. Respiration removes CO2
3. The kidney regulates the HCO3- in ECF

Question 5

CO2 and O2 are exchanged at the alveoli/pulmonary capillaries? What is the process?

Answer 5

Upon inhalation, 02 concentration in the alveoli increases and diffuses along a concentration gradient across the alveoli, interstitial fluid, endothelial wall and red blood cell wall. Here, O2 binds Hb and H+ is removed. H+ binds intracellular HCO3- to form H2CO3 which is broken down into CO2 and H2O by carbonic anhydrase. CO2 is now released to difffuse across the membranes and breathed off. Extra - Cl- is exchanged for HCO3- to provide the intracellular HCO3-. Some CO2 is bound to Hb before dissociating and diffusing.

Question 6

What happens to extracellular pH as ventilation rate increases.

Answer 6

It increases. Hyperventilation effectively removes more CO2 making the extracellular environment less acidic.