2.22 - Respiratory Acid Base Balance

Question 1

What are the largest chemical buffers in our body?

Answer 1

ECF: inorganic H2PO4-, plasma proteins
ICF: Cellular proteins and organic
HPO4- Bone: Mineral H2PO4-

Question 2

What are the limitations of these chemical buffers?

Answer 2

Although these buffers minimise pH change, they do not remove the acid or base from the body

Question 3

How does haemoglobin work as a buffer?

Answer 3

Hb can bind and release H+ ions, therefore acts as buffer.

Question 4

How does haemoglobin acting as a buffer relate to the Bohr Effect?

Answer 4

The Bohr Effect is an increase in blood CO2 concentration which leads to a decrease in blood pH will result in hemoglobin proteins releasing their load of oxygen.
The Bohr effect is due to ↑ [H+] (and therefore ↓pH) resulting in a right shift of the Hb-O2 dissociation curve. At a given PO2, Hb will have a lower O2 saturation –> more unloading.

Question 5

Why is Bicarbonate such a good buffer?

Answer 5

Components HCO3 + CO2 are abundant
System is open
Controlled by both lungs and kidneys

Question 6

What is the bicarbonate buffer equation?

Answer 6

H20 + CO2 H2CO3 HCO3- + H+

Question 7

What is the Henderson-Hasselbalch Equation?

Answer 7

pH = 6.1 + log [HCO3-] / [CO2]
Normal pH requires HCO3-:CO2 = 20:1
In equation PCO2 expressed as mmol/L
To convert to PCO2 * 0.03
pH = 6.1 log [HCO3-]/ (0.03 * PCo2)

Question 8

What does it term ‘open’ mean in relation to the bicarbonate buffer system being open?

Answer 8

Means that the components of the system can be added or removed from the body at controlled rates, achieved by three mechanisms

1. metabolism provides large stores of CO2
2. respiration can change the amount of CO2 in the ECF
3. Kidneys can change the amount of HCO3- in the ECF

Question 9

How does pH have an effect on ventilation?

Answer 9

An increase in [H+] (or decrease in pH) resulting in an increase in alveolar ventilation. This leads to decreased CO2 and therefore a reduced [H+]