Chapter 31 - Acid Base Regulation Flashcards
H+ secretion and HCO3 reabsorption occur in virtually all parts of the tubules except in ()
- descending thin limb of the LOH
- ascending thin limb of the LOH
For each HCO3 reabsorbed, what is secreted?
Hydrogen ion
Which segments secrete hydrogen ions into the tubular fluid (renal lumen) by sodium-hydrogen counter-transport (exchanger protein)
- proximal tubule
- thick segment of the ascending LOH
- early distal tubule
The sodium gradient for the sodium-hydrogen exchanger protein in the luminal membrane is established by
Na-K ATPase pump in the basolateral membrane
(1)% of the bicarbonate is reabsorbed for every (2)mEq of H+ secreted everyday
(1) 95%
(2) 4000 mEq
Normal H+ concentration of body fluids
0.00004 mEq/L
Rapidly dissociates and releases especially large amounts of H+ in solution
Ex. HCl
Strong Acid
Less likely to dissociate their ions, release H+ with less vigor
Ex. H2CO3
Weak Acid
One that reacts rapidly and strongly with H+ hence quickly removes H+ from a solution
Ex. OH- (which reacts with H+ to form H2O)
Strong Base
Binds with H+ more weakly
Ex. HCO3-
Weak Base
Most important weak acid in the body
H2CO3 - Carbonic acid
Most important weak base in the body
HCO3- - Bicarbonate ions
Normal pH of the body is
pH 7.4
pH 7.35 - 7.45
pH and H+ concentration of Body Fluids
Most acidic is Gastric acid (HCl)
Normal Arterial Blood pH: (1)
pH for acidosis: (2)
pH for alkalosis: (3)
(1) pH = 7.4
(2) pH < 7.4
(3) pH > 7.4
3 primary systems that regulate the H+ conc. In the body fluids to prevent acidosis/alkalosis
(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
(True/False)
Buffers stabilize pH by eliminating H+ or adding them to the body
False
Buffers DO NOT eliminate H+ from or add them to the body. They only keep them tied up
Any substance that can reversibly bind H
Buffer
Explain the Bicarbonate Buffer System
Solubility coefficient of CO2 at body temperature
0.03 mmol/mmHg
(1) Acid-base balance shift in Increase in HCO3-
(2) Regulated by
(1) Alkalosis
(2) kidneys
(1) Acid-base balance shift in increase in PCO2
(2) Regulated by
(1) Acidosis
(2) rate of respiration
4 Major Acid-Base Disorders
- Respiratory acidosis
- Respiratory alkalosis
- Metabolic acidosis
- Metabolic alkalosis
Acidosis caused by a primary decrease in HCO3- conc
Metabolic acidosis
Alkalosis caused by a primary increase in HCO3- concentration
Metabolic alkalosis
Acidosis caused by an increase in PCO2
Respiratory acidosis
Alkalosis caused by a decrease in PCO2
Respiratory alkalosis
Explain the Phosphate Buffer System
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)
Phosphate buffer system
Buffer in RBC
Hemoglobin (HB)
About (1) mol/L of dissolved CO2 is normally in the extracellular fluid, corresponding to a PCO2 of (2)mmHg
(1) 1.2 mol.L
(2) 40 mmHg
CO2 is formed continually in the body by intracellular metabolic processes
Effect of the rate of alveolar ventilation to PCO2 in extracelular fluid
Increasing alveolar ventilation decreases extracellular fluid H+ concentration and raises pH
High alveolar ventilation, blows off increased amounts of CO2, which lowers PCO2 (ALKALINE)
Vice versa is true - increased H+ conc. will stimulate alveolar ventilation
H+ concentration CONTROL by the respiratory system is what type of feedback mechanism
Negative Feedback Mechanism
Daily, the body produces ()mEq of nonvolatile acids mainly from metabolism of proteins
Nonvolatile are not H2CO3 which cannot be excreted by the lungs
80 mEq
Function of the kidney to maintain acid-base balance
(1) kidney must reabsorb virtually all filtered HCO3
(2) Must secrete into the urine the daly production of nonvolatile acids
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
Kidneys regulate extracellular fluid H+ concentration through:
1) secretion of H+
2) reabsorption of filtered HCO3-
3) procuction of new HCO3-
Bicarbonate transport across the basolateral membrane is facilitated by
- early PCT: sodium-bicarbonate co transport
- late PCT, thick ascending LOH, collecting tubules & ducts: chloride-bicarbonate exchange protein
(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
True
excess hydrogen (80 mEq/day) rids the body of nonvolatile acids produced by metabolism - excreted as phosphate and ammonia
Hydrogen secretion in the late distal tubules to the collecting ducts is via
Primary active transport
Primary active secretion of H+ occurs in what cells of the late distal tubule and in the collecting tubules
Type A Intercalated cells
(1) Most important buffers in urine
(2) other weak buffer system in urine
(1) phosphate and ammonia buffer system
(2) urate and citrate
Phosphate Buffer system carries excess H+ into the urine and generates new bicarbonate
Excretion of Excess H+ and generation of new HCO3 by ammonia buffer system
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
Glutamine is transported in which part of the kidney
(1) PCT
(2) thick ascending limb of LOH
(3) DCT
REGULATION OF RENAL TUBULAR H+ SECRETION
