6. Renal Control of Acid-Base

Question 1

What are fixed acids?

Answer 1

non-carbonic acids generated metabolically like sulfuric and phosphoric acids
Initially neutralized by buffers in body fluids and ultimately excreted in urine

Question 2

What are the metabolic sources of H?

Answer 2

oxidative metabolism of CO2
Fixed: glycolysis (lactic acid), incomplete FA oxidation (ketones), Protein, nucleic acid, phospholipid metabolism (sulfuric, phosphoric, hydrochloric acids)

Question 3

What is the primary buffer system?

Answer 3

bicarb/CO2 buffer

Question 4

What are the ECF buffer systems?

Answer 4

bicarb/CO2
inorganic phosphate (HPO4)
Plasma proteins

Question 5

What are the ICF buffers?

Answer 5

Cell proteins (hemoglobin)
Organic phosphates (ATP, 2,3 DPG)
Bicarb/CO2

Question 6

What is the Henderson-Hasselbalch equation?

Answer 6

pH = pK + log [A-]/[HA]

A- = HCO3
HA = CO2 or CO2 = (0.03*PCO2)

Question 7

What are volatile acids?

Answer 7

Produced by metabolic processes that can be expired by respiratory tract
Carbonic acid system

Question 8

What is the renal response to excess acid?

Answer 8

all of filtered HCO3 is reabsorbed and additional H is secreted into lumen, excreted primarily as ammonium

Question 9

What is the renal response to excess base?

Answer 9

Incomplete reabsorption of filtered HCO3
Decreased H secretion
secretion of HCO3 in collecting duct

Question 10

Most H is excreted in combination with urinary buffers. What are the two types?

Answer 10

Titratable acid: conjugated bases of metabolic acids accept H in lumen (phosphate, creatinine, urate)

Ammonia: generated by tubular epithelium

Question 11

H excretion = ?

Answer 11

urinary excretion of titratable acid + ammonium - HCO3

Question 12

HCO3 excretion is equivalent to adding ___ to body fluids

Answer 12

acids

*for each mEq of HCO3 lost, a free H is left behind

Question 13

Where is a major site for the formation of ammonia ?

Answer 13

Proximal tubule when glutamine is converted to ammonia

Question 14

What do alpha - intercalated cells secreted?

Answer 14

H by H ATPase pump

Question 15

What do beta - intercalated cells secrete?

Answer 15

HCO3 to eliminate excess base

HCO3/Cl exchanger

Question 16

The activity of H-ATPase in the alpha-intercalated cells are directly stimulated by what?

Answer 16

Aldosterone

Question 17

acid base status of hyperaldosterone patient

Answer 17

alkalosis

and hypokalemic

Question 18

Most of the H secreted by the proximal tubule is used to do what?

Answer 18

reabsorb filtered HCO3 so luminal pH falls only slightly in this segment

Question 19

Why must all of the filtered HCO3 needs to be reclaimed in normal individuals?

Answer 19

because excretion of HCO3 has same effects as gaining H; excretion of even small fraction of filtered HCO3 would acidify body fluids

Question 20

How does HCO3 get across the membrane?

Answer 20

it temporarily is converted to CO2

Question 21

80% of the filtered HCO3 is reabsorbed in PT, what is this ultimately dependent on?

Answer 21

Na,K ATPase

Question 22

If there is an excess amount of HCO3 in the plasma, what is preventing the bicarb from being reabsorbed?

Answer 22

it is a saturable process and the antiporters are filled

Question 23

what is the most important buffer converted to titratable acid?

Answer 23

filtered HPO4

Question 24

What is the process of excretion of H as ammonium in the proximal tubule?

Answer 24

glutamine in the cells is converted to 2 ammonium. This is converted to ammonia so that it can freely pass through the membrane to the tubular fluid. The Na/H exchanger pushes H out into the tubular fluid and joins NH3 and is excreted as ammonium. Also 2 bicarbs are produced by glutamine oxidation

Question 25

What are the factors controlling renal H secretion?

Answer 25

``` intracellular pH Plasma PCO2 CA activity Na reabsorption (angiotensin/aldosterone) Extracellular [K] aldosterone ```

Question 26

What is hyperchloremic acidosis?

Answer 26

when metabolic acidosis occurs and anion gap is unchanged due to loss of HCO3 is matched by gain of Cl

Question 27

What is normochloremic acidosis?

Answer 27

It is a high anion gap that occurs in metabolic acidosis due to HCO3 being replaced by unmeasured anion (lactate, ketoacidosis, poisoning)

Question 28

What are some causes of anion gap?

Answer 28

``` E. Elm Park ethanol ethylene glycol lactic acid methanol paraldehyde aspirin renal failure ketone bodies or MUDPILES ```

Question 29

What is MUDPILES?

Answer 29

``` methanol uremia diabetic ketoacidosis, starvation or alcoholic ketoacidosis paraldehyde iron lactic acidosis ethylene glycol salicylate ```