Acid and base Regulation

Question 1

What is the most important buffer in the body?

Answer 1

H+ –> HCO3- —> H2C03 H20 + CO2

Question 2

What are the normal pH values for arterial and venous blood?

Answer 2

Arterial - 7.4

Venous - 7.35

Question 3

What are the normal HCO3 ion concentration for arterial and venous blood?

Answer 3

Arterial - 24mM

Venous - 25mM

Question 4

What are the normal PCO2 for arterial and venous blood?

Answer 4

Arterial - 5.3 kPa

Venous - 6.1 kPa

Question 5

What is the H-H equation?

Answer 5

HA H+ + A-

Question 6

What is the Henderson Hasselbalch equation?

Answer 6

pH = pK +log (base)/ acid

Question 7

What is the normal extracellular pH?

Answer 7

7.4

Question 8

Give the equation to prove the normal extracellular pH using normal values?

Answer 8

pH = 6.1 + log 25/0.22 x 5.5

=7.4

Question 9

When does net hydrogen ion production occur?

Answer 9

ATP hydrolysis
anaerobic respiration with the production of lactate
production of ketones (diabetes mellitus)
ingestion of acids.

Question 10

How can excess H+ ions be removed in the short term?

Answer 10

H+ can react with the bicarbonate ions (HCO3-) producing CO2 and H20 which can then be removed.

Question 11

How is bicarbonate reabsorbed from the filtrate?

Answer 11

20% of bicarbonate is reabsorbed:

H+ ions are secreted into the filtrate through Na transporters.
Here H+ reacts with HCO3- ions forming CO2 and H2O.
CO2 and H2O can therefore enter into the epithelial cells where they get broken down by carbonic anhydrase reproducing HCO3- ions.
The bicarbonate ions are then returned into the body by a Na co-transporter.

Question 12

How does the transport maximum (Tm) for bicarbonate occur?

Answer 12

When there is low HCO3- ions in the filtrate then they can easily and quickly be absorbed.
At higher concentrations, there is a limiting factor which only allows HCO3- ions to be absorbed at a specific rate.

Question 13

What is the normal rate of HCO3- reabsorption?

Answer 13

~ 4mmol.min-1

Question 14

Why is the kidney special in the reabsorption of HCO3- ions?

Answer 14

The kidney separate the bicarbonate ions from the hydrogen ions as H ions go in the urine.
Elsewhere in the body both H+ and HCO3- ions are absorbed and therefore the is little difference in their concentrations.

Question 15

What is the main H+ secretion mechanism in the distal tubule?

Answer 15

Primary active transport via H+K+ ATPase and H+ ATPase.

This process occurs in the alpha - intercalated cells

Question 16

What is the key mechanism for filtrate buffering of H+ ions?

Answer 16

Filtrate phosphate.

Binding or sequestration of hydrogen phosphate.

Question 17

What is the phosphate buffer equation?

Answer 17

H+ + HPO4(2-) H2PO4-

Question 18

What is the normal state of phosphate in the body?

Answer 18

HPO4(2-)

at pH 7.4

Question 19

What is the state of phosphate in the urine (eg. at a pH of 5)?

Answer 19

This then shows that in acidic urine, H2PO4- phosphate state predominates and that phosphates are buffering the pH

Question 20

How can ammonia secretion help with the removal of H+ ions?

Answer 20

Ammonium ion is produced in the PCT by the conversion of glutamine to glutamic acid and alpha-ketoglutarate.

NH4+ is in eqm with NH3 and therefore can pass through membranes

NH4+ reforms in the filtrate lumen acting as another reservoir for H+ ions.

Question 21

What happens to the pH along the nephron?

Answer 21

By the end of the proximal tubule, the pH has fallen to about 6.9.
By the end of the tubule the pH is highly variable (depending of the body’s acid load) down to about pH 4.5

Question 22

What are the main clinical problems of Acid-Base regulation issues?

Answer 22

Respiratory acidosis
Respiratory Alkalosis
Metabolic Acidosis
Metabolic Alkalosis

Question 23

What is the Davenport diagram?

Answer 23

A graph the shows the pH against the HCO3- concentrations.

The lines show how changing HCO3- conc changes pH at a constant CO2.

Question 24

What is the typical cause of respiratory acidosis?

Answer 24

Hypoventilation:
Leads to increased CO2
therefore H+ increases and the pH falls.
To compensate the kidney increases the production of HCO3- to return the pH towards normal.

Question 25

What is the typical cause of metabolic acidosis?

Answer 25

Renal failure/lactic acidosis:
H+ increases so HCO3- decreases.
To compensate the CNS increases the ventilation rate decreasing CO2 returning the pH towards normal.