9_HST110 Acid-Base Physiology 2017

Question 1

Name 1 volatile acid and the mechanism of production in and clearance from the body

Answer 1

Cabonic acid produced from metabolism of carbohydrates and fats and hydrated from CO2 into H2CO3, excreted by lungs at CO2

Question 2

Name 2 examples of non-volatile acids (inorganic), their production method, and mechanism of clearance from body

Answer 2

Sulfuric acid, phosphoric acid. Metabolism of proteins. Excreted by kidneys

Question 3

What is the formula for calculating pH?

Answer 3

pH = -log [H+]

Question 4

What is the plasma concentration of hydrogen ion?

Answer 4

40 nM (pH 7.4)

Question 5

Name 3 adverse effects of dysregulated H+

Answer 5

Impaired cardiac contractility, arrythmias, and changes in O2 carrying capacity

Question 6

What mechanisms regulate [H+] and what are their timescales?

Answer 6

Buffer systems (first line) (Instantaneous)

Lungs (second line) (seconds to minutes)

Kidneys (third line) (Slowly, transporters involved. Days)

Question 7

Name the major physiologic buffer system

Answer 7

Bicarbonate (HCO3-), regulated by both lungs and kidneys. CO2+H2O (slow, rate limiting) H2CO3 (fast) H+ +HCO3-

Question 8

What is the Henderson-Hasselbalch eqn. for the bicarbonate buffer system?

Answer 8

pH = 6.1 + log([HCO3-]/(0.03*PCO2))

Question 9

Disturbances that cause a change in [HCO3-] are (X) acid-base disorders

Disturbances that cause a change in PCO2 are (Y) acid-base disorders

Answer 9

X = metabolic
Y = respiratory

Question 10

Sources of Acid and Alkali

Answer 10

Dietary intake, cell metabolism, fecal loss (HCO3- lost in stool)

Question 11

Approximately (X) mEq/kg body weight of nonvolatile acid is added to the body each day ((Y) mEq/day)

Answer 11

X = 1
Y = 50-100

Daily Acid-Base Balance skewed in favor of acid

Question 12

Systemic acid-base balance is maintained when

Renal net acid excretion = (X)

Answer 12

X = Net acid production

Question 13

Kidneys’ “Triple Play” maintains acid-base balance: Name the 3 steps the kidney takes

Answer 13

Under normal circumstances, the kidneys:

1. Excrete acid equal to amount produced
2. Reabsorb filtered HCO3-
3. Generate new HCO3- to replenish what is lost by neutralizing nonvolatile acids

Question 14

Renal Net Acid Excretion: Excreting acid and reabsorbing (X) are achieved by secreting H+ through the (Y) antiporter coupled to ammonium excretion

Answer 14

X = HCO3-
Y = Na+-H+

Question 15

Majority of H+ secretion into tubular fluid used to reabsorb filtered (X). (Y) mEq/day actually excreted into urine

Answer 15

X = HCO3-
Y = 50-100

Question 16

Because of acid excretion, urine pH is normally (X)

Answer 16

X = acidic

Question 17

What are the 2 primary mechanisms for excreting H+?

Answer 17

Ammonium (NH4+) (2/3)

Titratable acid (1/3)

Question 18

What is the major urinary buffer?

Answer 18

Ammonium (NH4+)

Produced in tubular cells by metabolism of glutamine

Question 19

Mechanisms of NH4+ buffering:

NH4+ secreted into lumen via (X) antiporter (PT)

NH3 diffuses into lumen, binds H+ to form NH4+ in the (Y)

Answer 19

X = Na+-H+
Y = Collecting Duct

Question 20

Titratable Acid: Kidneys excrete H+ with urinary buffers

(X) is the major titratable acid

Other TA’s:
creatinine
urate
lactate
β-hydroxybutyrate

(Y) mEq/day of H+ buffered by titratable acids

Answer 20

X = Phosphate
Y = 10-40

Question 21

Mechanism of Titratable Acid - Phosphate:

Secreted H+ is trapped by urinary phosphate and excreted in urine

HCO3- is added to the blood as (X) HCO3-

Answer 21

X = new (non-filtered)

Question 22

How much HCO3- is filtered by glomerulus?

Answer 22

~4320 mEq/day

Question 23

Kidneys need to reabsorb virtually all  filtered HCO3-
Mostly in (X) (80%). Reabsorption of HCO3- is coupled with secretion of (Y)

Answer 23

X = proximal tubule
Y = H+

Question 24

What are the key mediators of reabsorption of HCO3- int the proximal tubule?

Answer 24

Apical
NHE3
H+-ATPase

Basolateral
NBCe1

Question 25

What are the key mediators of reabsorption of HCO3- int the distal tubule?

Answer 25

α-intercalated cells:

• Secrete H+
• Reabsorb HCO3-
• Predominate under normal conditions

β-intercalated cells

• Secrete HCO3-
• Reabsorb H+
• Incresaed activity in metabolic alkalosis

Question 26

Renal Generation of New HCO3-: Kidneys must generate new HCO3- to replace the loss

Excretion of H+ with titratable acids
CRUCIALLY: Excretion of (X)

Answer 26

X = NH4+

Question 27

Production of New HCO3- through NH4+: Step 1

NH4+ is produced by the metabolism of (X) in the proximal tubule

Breakdown of 1 glutamine generates:
2 molecules of NH4+
2 molecules of HCO3-

NH4+ enters lumen:
via (Y) antiporter
via diffusion as NH3

(Z) exits into the blood

Answer 27

X = glutamine
Y = Na+-H+
Z = HCO3-

Question 28

Production of New HCO3- through NH4+: Step 2

NH4+ produced by the proximal tubule is then reabsorbed in the (X)

Transported by (Y) symporter (subs for K+)

Accumulates in medullary interstitium and exists in chemical equilibrium with (Z) (pKa = 9.0)

Answer 28

X = TAL
Y = Na+-K+-2Cl-
Z = NH3

Question 29

Production of New HCO3- through NH4+: Step 3

NH4+ secreted by (X) into tubular fluid by two mechanisms:

1. Active transport across intercalated cells
   * in via (Y), out via H+-K+-ATPase
2. (Z)

Answer 29

X = collecting duct
Y = Na+-K+-ATPase
Z = Nonionic diffusion / diffusion trapping

Question 30

NH4+ Excretion: Nonionic Diffusion / Diffusion Trapping:

NH3 diffuses from (X) into lumen of CD

NH3 is protonated to NH4+ by acidic tubular fluid* (pH 4.0-4.5)

NH4+ is “trapped” in lumen because CD is (Y) permeable to NH4+ than to NH3

NH4+ is excreted in urine

Answer 30

X = medullary interstitium
Y = less