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+, reabsorption and regeneration of HCO3-
4. Intracellular buffering (HCO3-, PO4-, proteins).

Question 2

What is the effect of a drop in pH on the dissociation of Hb and O2?

Answer 2

A drop in pH decreases Hb affinity for O2. Hb will bind to H+ in preference to O2 (more of it around).

Question 3

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

Answer 3

HCO3- decreases in metabolic.
CO2 increases in respiratory.
(Hendersen-Hasselbach)

Question 4

How is the bicarbonate system “open”?

Answer 4

Open because reactants and products are replenished and removed.
1 - Metabolism continues to produce CO2.
2 - Respiration removes CO2
3 - Kidney regulates HCO3-

Question 5

CO2 and O2 are exchanged in the alveoli. 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 (more basic). Hyperventilation reduces CO2.