Renal Physiology 7 - Checked and Complete

Question 1

Describe the difference between volatile and fixed acids.

Answer 1

Fixed acids are produced metabolically and don’t change as dynamically as volatile acids. Examples of fixed acids include: lactic acid and sulfuric acid

CO₂ is a volatile acid because it can enter/escape the solution as a gas - much more dynamic process

Question 2

What happens to bicarbonate concentration when acid is added to the system, lost?

Answer 2

Added acid = Bicarb used up and released as CO₂and H₂O

Loss of acid = build up of bicarb because CO₂ and H₂O combine

Question 3

Define the Henderson-Hasselbalch equation

Answer 3

pH = 6.1 + Log([HCO₃]/.03 x P_CO2)

Question 4

What are typical values of Bicarb, CO2, pH

Answer 4

Bicarb = 24

CO2 = 40

pH = 7.4

Question 5

What is the daily turnover of acids/bases?

Answer 5

Body gains about 60mEqs of acid each day

20 from diet, 20 from metabolic leftovers, 20 from loss of base in feces

Thus, the kidneys need to excrete about 60mEqs of acid in the urine

Question 6

Describe filtration of H+ ions

Answer 6

Only 0.0072 mEq of hydrogen ions filtered per day

MUST rely on secretion to remove 60mEqs of acid from the body

Question 7

What is the form of hydrogen ions in the urine?

Answer 7

The urine has bound hydrogen ions, not mostly free

Urine pH rarely lower than 4.5

Question 8

Describe Bicarb reabsorption from the PCT.

Answer 8

80% reabsorbed at PCT transcellularly

Apically, a Na-H-antiporter secretes hydrogen into nephron lumen

Hydrogen binds bicarb and CO2 and H20 diffuse out of nephron

They dissociate inside the cell

HCO3 - is moved across the basolateral membrane by the Na-HCO3 symporter

This is fuel for sodium to be reabsorbed

Cycle continues

Question 9

How much bicarb is reabsorbed in the thick ascending limb of loop of Henle?

Answer 9

~15%

Question 10

Describe cortical collecting duct reabsorption of bicarb

Answer 10

1) Hydrogen secreted apically via H+/K+ ATPase and also H+/ATPase

2) Hydrogen associates with bicarb, equilibrates into cell, dissociates

3) Bicarb transported basolaterally by Cl-/bicarb antiporter

Question 11

Where is carbonic anhydrase located?

Answer 11

In the PCT nephron lumen on (apical surface on nephron side)

It creates H₂CO₃out of Hydrogen and bicarb

Question 12

How does the kidney handle excess base?

Answer 12

Absorbs less

Excretes bicarb at the cortical collecting duct

Question 13

Describe the difference between type A and type B intercalated cells of the cortical collecting duct.

Answer 13

Type A ABSORB bicarb

Type B secrete bicarb

Are simply flip-flopped versions of each other

(Type B has basolateral ATP pumps which push hydrogen ions into the interstitium; bicarb/chloride antiporter in apical membrane for secretion)

Question 14

Describe renal handling of excess acid

Answer 14

1) Hydrogens are secreted from Type A intercalated cells per usual

2) Instead of bicarb binding these hydrogen ions, Phosphates bind these ions (monohydrogenphosphate to be precise)

**3) Bicarb formation is favored because Hydrogens are whisked away **

4) Double benefit - more bicarb, less hydrogen

Question 15

Describe why it is important that dihydrogen phosphate is a titratable acid.

Answer 15

The phosphate bound by hydrogens can be titrated with a strong base until the urine’s pH is equal to that of plasma

The amount of base added = amount of acid excreted = amount of bicarb produced by body

Question 16

What do hydrogen ions bind to in the urine?

Answer 16

Bind to phosphates and ammonia

Question 17

Describe acid reduction based on ammonia use

Answer 17

Hydrogen actively secreted into nephron lumen

Ammonia binds it and bicarb is formed, pulled back into blood

Ammonia comes from Glutamine and is an “on demand” process

Question 19

How do you calculate net gain/loss of bicarb from the body?

Answer 19

**Net HCO₃^- = Total New HCO₃ - Urine HCO₃ **

**Total new HCO₃found by considering urine ammonium levels and titratable H₂PO₄ **

**** The number of free H+ ions in even very acidic urine (pH 4.5) is trivial **

Question 20

What signals H+ secretion to increase or decrease in the kidneys?

Answer 20

Plasma CO2 level

Arterial blood pH

Question 21

Define respiratory acidosis

Answer 21

** High plasma P_CO2 because of reduced respiration**

Possibly caused by muscular dystrophy, sleep apnea, MS, emphysema

Question 22

Define metabolic acidosis

Answer 22

** low plasma HCO3 - concentration**

Potentially caused by diabetes, lactic acidosis, diarrhea, and advanced renal failure

Question 23

What is the normal ratio of bicarb:P_CO2x .03?

Answer 23

20

lower than this = acidosis

higher than this = alkalosis

Question 24

How do you clinically define acidosis/alkalosis?

Answer 24

Acidosis < 7.35

Alkalosis > 7.45

Question 25

Define repiratory alkalosis

Answer 25

low P_CO2from excessive ventilation

Question 26

Define metabolic alkalosis

Answer 26

Higher than normal serum bicarb

Vomiting, Hyperaldosteronism and Cushing’s’ disease

Question 27

How do the kidneys compensate for acidosis?

Answer 27

Secrete more H+ (often seen as high ammonium concentration)

Question 28

How do the kidneys compensate for alkalosis?

Answer 28

Reduce bicarb reabsorption

** Reduce production/excretion of NH4 + and titratable acids **

Goal is to reduce plasma HCO3 concentration

Question 29

Define the anion gap.

Answer 29

**The difference between the concentration of the MAJOR plasma cation (Na⁺ ) and the MAJOR plasma anions (Cl^- and HCO3^- ). **

The real concentration of all negative (anions) and positive (cations) charges in any compartment in the body is always the same

Question 30

What is the normal range for anion gap

Answer 30

12mM is normal

8-16 mM

Question 31

Provide normal values for the plasma concentration of sodium, chloride, and bicarb.

Answer 31

Sodium ~140 mM

Chloride ~102 mM

Bicarb ~24 mM

Question 32

How can an increase in fixed acid influence the anion gap?

Answer 32

Introduction of new acids (thus new hydrogen ions with new anions) will not be counted in calculating the anion gap.

Anion gap will increase if acid is present.

Question 33

Where does ammonium enter the tubular lumen?

Answer 33

At the PCT