Chapter 31 - Acid Base Regulation

Question 1

H+ secretion and HCO3 reabsorption occur in virtually all parts of the tubules except in ()

Answer 1

• descending thin limb of the LOH
• ascending thin limb of the LOH

Question 2

For each HCO3 reabsorbed, what is secreted?

Answer 2

Hydrogen ion

Question 3

Which segments secrete hydrogen ions into the tubular fluid (renal lumen) by sodium-hydrogen counter-transport (exchanger protein)

Answer 3

• proximal tubule
• thick segment of the ascending LOH
• early distal tubule

Question 4

The sodium gradient for the sodium-hydrogen exchanger protein in the luminal membrane is established by

Answer 4

Na-K ATPase pump in the basolateral membrane

Question 5

(1)% of the bicarbonate is reabsorbed for every (2)mEq of H+ secreted everyday

Answer 5

(1) 95%
(2) 4000 mEq

Question 6

Normal H+ concentration of body fluids

Answer 6

0.00004 mEq/L

Question 7

Rapidly dissociates and releases especially large amounts of H+ in solution

Ex. HCl

Answer 7

Strong Acid

Question 8

Less likely to dissociate their ions, release H+ with less vigor

Ex. H2CO3

Answer 8

Weak Acid

Question 9

One that reacts rapidly and strongly with H+ hence quickly removes H+ from a solution

Ex. OH- (which reacts with H+ to form H2O)

Answer 9

Strong Base

Question 10

Binds with H+ more weakly

Ex. HCO3-

Answer 10

Weak Base

Question 11

Most important weak acid in the body

Answer 11

H2CO3 - Carbonic acid

Question 12

Most important weak base in the body

Answer 12

HCO3- - Bicarbonate ions

Question 13

Normal pH of the body is

Answer 13

pH 7.4
pH 7.35 - 7.45

Question 14

pH and H+ concentration of Body Fluids

Answer 14

Most acidic is Gastric acid (HCl)

Question 15

Normal Arterial Blood pH: (1)
pH for acidosis: (2)
pH for alkalosis: (3)

Answer 15

(1) pH = 7.4
(2) pH < 7.4
(3) pH > 7.4

Question 16

3 primary systems that regulate the H+ conc. In the body fluids to prevent acidosis/alkalosis

Answer 16

(1) chemical acid-base buffer systems of body fluids: combine to acids or bases to neutralize

(2) respiratory center: regulate removal of CO2 and carbonic acid from ECF

(3) kidneys: excrete excess acid or base

Question 17

(True/False)

Buffers stabilize pH by eliminating H+ or adding them to the body

Answer 17

False

Buffers DO NOT eliminate H+ from or add them to the body. They only keep them tied up

Question 18

Any substance that can reversibly bind H

Answer 18

Buffer

Question 19

Explain the Bicarbonate Buffer System

Answer 19

Question 20

Solubility coefficient of CO2 at body temperature

Answer 20

0.03 mmol/mmHg

Question 21

(1) Acid-base balance shift in Increase in HCO3-

(2) Regulated by

Answer 21

(1) Alkalosis

(2) kidneys

Question 22

(1) Acid-base balance shift in increase in PCO2

(2) Regulated by

Answer 22

(1) Acidosis

(2) rate of respiration

Question 23

4 Major Acid-Base Disorders

Answer 23

1. Respiratory acidosis
2. Respiratory alkalosis
3. Metabolic acidosis
4. Metabolic alkalosis

Question 24

Acidosis caused by a primary decrease in HCO3- conc

Answer 24

Metabolic acidosis

Question 25

Alkalosis caused by a primary increase in HCO3- concentration

Answer 25

Metabolic alkalosis

Question 26

Acidosis caused by an increase in PCO2

Answer 26

Respiratory acidosis

Question 27

Alkalosis caused by a decrease in PCO2

Answer 27

Respiratory alkalosis

Question 28

Explain the Phosphate Buffer System

Answer 28

Question 29

Plays a minor role as an extracellular buffer but is important in buffering the tubular fluids of the kidneys and intracellular fluid pK (6.8)

Answer 29

Phosphate buffer system

Question 30

Buffer in RBC

Answer 30

Hemoglobin (HB)

Question 31

About (1) mol/L of dissolved CO2 is normally in the extracellular fluid, corresponding to a PCO2 of (2)mmHg

Answer 31

(1) 1.2 mol.L (2) 40 mmHg ## Footnote CO2 is formed continually in the body by intracellular metabolic processes

Question 32

Effect of the rate of alveolar ventilation to PCO2 in extracelular fluid

Answer 32

Increasing alveolar ventilation decreases extracellular fluid H+ concentration and raises pH **High alveolar ventilation, blows off increased amounts of CO2, which lowers PCO2 (ALKALINE)** ## Footnote Vice versa is true - increased H+ conc. will stimulate alveolar ventilation

Question 33

H+ concentration CONTROL by the respiratory system is what type of feedback mechanism

Answer 33

Negative Feedback Mechanism

Question 34

Daily, the body produces ()mEq of nonvolatile acids mainly from metabolism of proteins ## Footnote Nonvolatile are not H2CO3 which cannot be excreted by the lungs

Answer 34

80 mEq

Question 35

Function of the kidney to maintain acid-base balance

Answer 35

(1) kidney must reabsorb virtually all filtered HCO3 (2) Must secrete into the urine the daly production of nonvolatile acids ## Footnote Renal excretion is the primary mechanism for removal of nonvolatile acids, but a task more important is the prevention of loss of bicarbonate in the urine

Question 36

Kidneys regulate extracellular fluid H+ concentration through:

Answer 36

1) secretion of H+ 2) reabsorption of filtered HCO3- 3) procuction of new HCO3-

Question 37

Bicarbonate transport across the basolateral membrane is facilitated by

Answer 37

* early PCT: sodium-bicarbonate co transport * late PCT, thick ascending LOH, collecting tubules & ducts: chloride-bicarbonate exchange protein

Question 38

(True/False) Bicarbonate and hydrogen ion normally "titrate" each other in the kidney tubules. This is however not exact where excess hydrogen in the tubules are the ones to be excreted in the urine

Answer 38

True excess hydrogen (80 mEq/day) rids the body of nonvolatile acids produced by metabolism - excreted as phosphate and ammonia

Question 39

Hydrogen secretion in the late distal tubules to the collecting ducts is via

Answer 39

Primary active transport

Question 40

Primary active secretion of H+ occurs in what cells of the late distal tubule and in the collecting tubules

Answer 40

Type A Intercalated cells

Question 41

(1) Most important buffers in urine (2) other weak buffer system in urine

Answer 41

(1) phosphate and ammonia buffer system (2) urate and citrate

Question 42

Answer 42

Phosphate Buffer system carries excess H+ into the urine and generates new bicarbonate

Question 43

Excretion of Excess H+ and generation of new HCO3 by ammonia buffer system

Answer 43

Notes: * ammonium ion is synthesized from glutamine (amino acid metabolite from liver) * Glutamine forms 2 ammonia and 2 bicarbonate in the kidney cell * ammonia is released in lumen via counter transport with sodium

Question 44

Glutamine is transported in which part of the kidney

Answer 44

(1) PCT (2) thick ascending limb of LOH (3) DCT

Question 45

REGULATION OF RENAL TUBULAR H+ SECRETION

Answer 45