Physiology - Acid Base Balance

Question 1

Is blood slightly acidic or alkaline? What is the normal value?

What is more acidic arterial or venous blood?

Answer 1

Alkaline - 7.4

Venous - due to CO2

Question 2

Changes in [H+] influence (what ion) level in the body?

Answer 2

Potassium

Increase in [H+] = increase in H+ secretion = decrease in K+ secretion

(link to hyperkalaemia in DKA)

Question 3

How does a buffer work?

Answer 3

Pair of substances

• one can yield free H+ as the [H+] decrease
• one can bind free H+ as [H+] increases

Question 4

Why can the pH of the blood be described as pH = kidneys/lungs

Answer 4

pH = HCO3-/pCO2

Kidneys are responsible for HCO3-

Lungs are responsible for pCO2

Question 5

Is the majority of HCO3- secreted or reabsorbed?

Where does this occur?

What enzyme is essential for this process?

Answer 5

Reabsorbed (unorthodox reabsorption)

Carbonic anhydrase

Question 6

What impact does an increase in CO2 have on H+ secretion?

Answer 6

Increases

Question 7

If HCO3- in the tubular fluid is lower, what do H+ bind with in the tubular fluid?

Through this process what else is produced which goes back into blood?

Answer 7

Phosphate

HCO3- to top up buffer solution

Question 8

Under what circumstances do hydrogen ion bind with ammonia to be excreted as ammonium?

Answer 8

When all phosphate and HCO3- have been used up

HCO3- is also produced back into bloodstream to increase buffer solution

Question 9

What is titratable acid?

Answer 9

Amount of H+ excreted as H2PO4 (when bound to phosphate) can be measured as ‘titratable’ acid

Question 10

How is tubular acid secretion rate measured?

From this how can ‘new’ HCO3- produced be calculated?

Answer 10

Tubular acid secretion =
1. How much HCO3- reabsorped
2. Titrable acid excretion (H2PO4) 
3. Ammonium (NH4+) excretion 
^add together^

New HCO3- produced =
1. Tiratable acid excretion
2. NH4+ excretion
^add together^

Question 11

If you have an acidosis caused by respiratory system. What system can help to balance the system again?

Answer 11

Renal compensation

Question 12

Hyperventilation leads to respiratory alkalosis or acidosis?

Answer 12

Alkalosis

Question 13

Would respiratory acidosis or metabolic acidosis have a high HCO3-?

Answer 13

Resp - high constant levels of CO2 = high levels of H+ = high levels of new HCO3-

Question 14

Draw and explain the Davenport diagram at the end of the Acid Base II PP

Answer 14

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