Acid-Base Balance

Question 1

ECF acidosis leads to what changes in K?

Answer 1

Hyperkalemia and decreased renal K excretion due to inhibition of ROMK

Question 2

ECF alkalosis leads to what changes in K

Answer 2

Hypokalemia and increase renal K excretion due to activation of ROMK

Question 3

What is a buffer?

Answer 3

A substance that preserves the original H-ion concentration when adding acids or bases. Offsets the reaction

Question 4

What are some buffers in the maintenance of acid- base homeostasis?

Answer 4

• Intra and extracellular buffers
• Regulation of breathing
• Long term by the kidneys

Question 5

Where is a buffer most effective?

Answer 5

Within 1 pH unit of its pKa

Question 6

What are some non-HCO3 buffers?

Answer 6

• hemoglobin
• organic phosphates
• inorganic phosphates
• plasma proteins
• intracellular proteins

Question 7

What ratio determines pH?

Answer 7

HCO3 to CO2

Question 8

Why are we able to buffer with a buffers whose pKa is so much lower than physiological pH?

Answer 8

It is an open system and ventilation adjusts to maintain pCO2

Question 9

What happens in respiratory acidosis?

Answer 9

CO2 and HCO3 increase. Acid is secreted and HCO3 is reabsorbed

Question 10

What happens in respiratory alkalosis?

Answer 10

Low on CO2 and HCO3 and the kidneys will secrete HCO3 and Cl - retention

Question 11

What is the effect of metabolic acidosis?

Answer 11

Acid is built up ie lactic acid build up and results in hyperventilation

Question 12

What is the effect of metabolic alkalosis?

Answer 12

Loss of acid which leads to hypoventilation

Question 13

What compensatory mechanism for acid/base load rakes the least amount of time?

Answer 13

ECF distribution

Question 14

What compensatory mechanism for acid/base load rakes the most amount of time?

Answer 14

Acid secretion. Have to turn on alpha intercalated cells

Question 15

How are strong acids eliminated?

Answer 15

The pKa of these is below urine pH so they remain dissociated and cannot be excreted in the acid form so have to use NH4 trapping

Question 16

How is ammonium generated in the PT?

Answer 16

Ammonia is made by the breakdown of gultamine. It is secreted into the lumen and equilibrates with NH4 and NH3 because the pH is below the pKa

Question 17

How is HCO3 absorbed in the proximal tubular reabsorption?

Answer 17

HCO3 in the lumen is converted into CO2 by CA. This can now diffuse into the cell and is converted back into HCO3 with H2O. The hydrogen ion gets pumped back into the lumen while HCO3 enters the blood through Na HCO3 cotransporters

Question 18

How is new HCO3 generated in the PT?

Answer 18

CO2 from the blood diffuses into the cell and with water gets converted to HCO3 and a hydrogen ion. The hydrogen ion is pumped into the lumen and HCO3 is pumped out through NaHCO2 pump into the blood

Question 19

What happens the the H ions that get put into the lumen at the PT?

Answer 19

These are buffered by weak acids conjugate base. Usually phosphate

Question 20

How is HCO3 created in the CD?

Answer 20

Co2 from the blood filters in alpha intercalated cells and is converted to HCO3 and pumped back in the blood with a HCO3/Cl pump and the H ion is pumped into the lumen and combines with a conjugate base of a weak acid

Question 21

What is the pH of urine as it leaves?

Answer 21

around 4.4

Question 22

How are strong acids excreted in the urine?

Answer 22

Because their pKa is below that of urine, they remain dissociated and are trapped in the lumen by combining with ammonia

Question 23

How is ammonia/ammonium produced in the PT?

Answer 23

Breakdown of glutamine

Question 24

Describe the process of NH4 trapping?

Answer 24

Ammonium is formed in the PT and travels in the loop of Henle until it reaches the TALH where it is reabsorbed in the interstitium by NKCC. Here it equilibrates to the NH4 and NH3 form. NH3 is able to cross into the CD and trap H ions and is unable to leave. Thus lowering pH