Renal: Acid Base Disorders

Question 1

What are some sources of volatile and non volatile acids produced by the body?

Answer 1

Metabolism of fats and carbohydrates make CO2→ carbonic acid
CO2 + H2O ⬄ H2CO3 ⬄ H+ + HCO3-
Carbonic acid is volatile, it comes out of solution and exhaled as C02, so rarely alters plasma pH
Protein metabolism produces non-volatile acids like H2SO4 and HCl
Non-volatile acids need to be removed by buffers or habrá net H+ gain, causing acidosis.

Question 2

Why is acid base balance so important?

Answer 2

Protein structure and function depend on [H+] and is very sensitive to changes, can get denatured.
Normal pH between 7.35-7.45. [H+] = 40nM (very low)
[H+] is maintained by buffers in kidneys, lungs, liver

Question 3

[H+] concentration changes due to…

Answer 3

Hydrogen ion concentrations change due to
•Metabolism of food
•Secretions of the gastrointestinal (GI) tract, (3) d
•Generation of acids and bases from metabolism of fat and glycogen
•Changes in the production of carbon dioxide.

Question 4

In the body, ECF + ICF buffer systems, and the respiratory and renal systems control pH. Give an example of an ECF buffer.

Answer 4

Major ECF buffer system is CO2-HCO3- system.
This system also found in blood:CO2 + H2O ⬄ H2CO3 ⬄ H+ + HCO3-

Question 5

Describe proximal tubular reabsorption of bicarbonate

Answer 5

In the lumen filtered bicarbonate combines w H+ to form CO2 and water (via CA)
C02 diffuses into the tubular cell and combines w water to form carbonic acid
This breaks into H+ which is excreted w Na/H exchanger
HCO3 moves into interstitium. Na is pumped into the interstitium

Basically the body converts bicarbonate to C02, which diffuses easily, para absorb bicarbonate- convenience
Bicarbonate is reabsorbed, H+ is excreted back into the lumen via Na H exchanger

Question 6

Describe Distal tubular H+ excretion

Answer 6

• H+ generated from H2O and CO2 is actively pumped out in lumen
• H+ in the lumen combines with HPO42-.
• This is a way to get rid of H+ in the DCT

Question 7

Describe Distal tubular ammonia secretion

Answer 7

• Also removes H+ ions, maintains pH
• Ammonia is generated from Glutamate
• NH4+ breaks into H+ and NH3, which diffuses out into lumen
• NH3 combines with H+. NH4+ is excreted in urine

Question 8

Use this diagram to summarise renal acid base excretion

Answer 8

Kidneys control acid-base levels via excretion of acidic/basic urine

Excretion of HCO3- → decreased blood pH.

H+ excretion→ increased pH

Question 9

What are the major buffers in the blood, interstitial fluid and and intracellular fluid?

Answer 9

Question 10

Describe the type of compensation that occurs in metabolic acidosis

Answer 10

Increased [H+] stimulates peripheral chemoreceptors, causes tachypnoea→ less PaCO2. Reducing CO2 level drives the buffer eqm to the right to remove H+

H+ + HCO3- ⬄ H2CO3 ⬄ CO2 + H2O

Renal compensation of metabolic acidosis involves max bicarbonate reabsorption/synthesis:

• it excretes excess H+ and increases plasma bicarbonate
• Ammonium secretion helps synthesise new bicarbonate from a-ketoglutatarate

Question 11

What type of compensation occurs in metabolic alkalosis?

Answer 11

Triggers peripheral chemoreceptors, reducing ventilation so less CO2 lost
PaCO2 rises → carbonic acid → increased [H+]
H+ used up in plasma to reduce bicarbonate levels
Increased tubular pH reduces H+ secretion and bicarbonate reabsorption

Question 12

Describe the function of regions the renal tubule in maintaining acid base balance

Answer 12