12 - Acid Base Balance

Question 1

why is urine profoundly acidic?

Answer 1

• 60 millimol (60 million nanomol) H+ are produced by metabolism daily
• need to excrete most or all of this
• [H+] is 35-45 nanomol/L so regulation very tight! - otherwise out of control very quickly

Question 2

why is bicarbonate so important?

Answer 2

• it’s the most important buffering system as other buffering systems reach equilibrium but this one doesn’t
  H+ + HCO3- ↔ H2CO3 ↔ CO2 + H2O
• so the only limit is initial concentration of HCO3-
  • if too much acid →to much on the right and then push to equilibrium - in this case that’s never reached. you breathe out CO2 and H2O

Question 3

what is the important rearrangement of bicarbonate buffering system?

Answer 3

[H+]=α pCO2 / [HCO3−]

Question 4

what is acidaemia?

Answer 4

↑ [H+]

Question 5

what is alkalaemia?

Answer 5

↓ [H+]

Question 6

what is acidosis?

Answer 6

A process tending to cause ↑ [H+]

Question 7

what is alkalosis?

Answer 7

A process tending to cause ↓ [H+]

Question 8

what is the metabolic component?

Answer 8

HCO3- (as used in buffering - produced by metabolisis)

Question 9

what is the respiratory component?

Answer 9

partial pressure of CO2

Question 10

what do you call increase in hydrogen concentration due to increased partial pressure of CO2?

Answer 10

respiratory acidosis

Question 11

what do you call decrease in hydrogen concentration due to decrease partial pressure of CO2?

Answer 11

respiratory alkalosis

Question 12

what do you call increase in hydrogen concentration due to decrease bicarbonate ion concentration?

Answer 12

metabolic acidosis

Question 13

what do you call decrease in hydrogen concentration due to increase bicarbonate ion concentration?

Answer 13

metabolic alkalosis

Question 14

what is examples of problem causing increase in H+ concentration?

Answer 14

• ketones (symptom of biochemical starvation - not enough glucose to provide energy for all processes - some of intermediates in this break down pathway to provide fuel are ketones which are profoundly acidic so release H+)
• lactic acid (end product of anaerobic glycolysis - produce acid so high H+)

= means drives reaction to the right

Question 15

what is examples of problem causing increase in CO2 production?

Answer 15

COPD (chronic obstructive pulmonary disease)and other pulmonary problems = ability to exchange gases is reduced so CO2 builds up

= reaction being driven to right

Question 16

what is example of problem causing too little H+ concentration?

Answer 16

loss of gastric HCl in prolonged vomiting (HCl produced in body for digesting food so when vomit you lose HCl)

= reaction being “pulled” toward the side of lacking H+

Question 17

what is example of problem causing too little CO2?

Answer 17

hyperventilation e.g. lung infections, asthma, panic attack

=reaction being “pulled” toward the side of lacking CO2

Question 18

how does body compensate for metabolic acidosis?

Answer 18

metabolic acidosis = too much H+ due to ketones & lactic acid etc

• compensate by blowing off CO2 (very distinct heavy breathing = acidotic breathing)
• you can also smell ketones (sickly sweet smell)

Question 19

how does body compensate for too much CO2?

Answer 19

compensate by excreting H+

• there is specific reaction that takes place in renal tubular cells where CO2 taken in from peritubular capillary and the reaction goes in reverse towards H+ and HCO3-. the HCO3- then leaves back into capillaries and H+ can go to the other side into renal tubular lumen (the HCO3- leaving means reaction doesn’t just reverse back again)

Question 20

what does body compensation aim to do?

Answer 20

• Think of compensation in terms of the ratio above – body always tries to return ratio to normal