Acid-base Balance and Ca2+ Homeostasis Flashcards
If the pH is less than ___ or greater than ___ life cannot be sustained because proteins will stop working.
6.8; 7.8
Why is too much acid the greatest concern?
because the body takes in (and/or produces) more acid than base
What two forms of acid should we be concerned about?
- volatile acids - these by-products of metabolism can be exhaled or dissipated by the lungs (eg CO2 is an acid because it produces H+ in the water of body fluids)
- nonvolatile acids - arise from metabolism or the diet (phosporic, latic, and sulfuric acids and ketones)
Nonvolatile acids must be neutralized with ___, are regulated by the ___ system, and neutralization requires continual replenishment of ___
HCO3-; renal; HCO3-
The amount of acid in the urine should equal the nonvolatile acid load. How does the kidney accomplish this?
By reabsorbing all of the filtered bicarbonate, and then producing enough new bicarbonate to neutralize acids produced by the body.
However, the lowest possible pH for the urine is ~4.4, which represents very little free H+ and this pH of the urine is not sufficient to excrete the nonvolatile acid load. Therefore, the kidney must excrete more acid than can be held in a solution with pH = 4.4.
How do buffers function in the urine?
They bind to excess of free H+ to increase acid carried in urine without decreasing pH
The kidney can produce ___ to act as a buffer, but it also adds ___ and ___ to the filtrate to increase the amount of H+ excreted
HCO3-; phosphate; ammonium
Phosphate is used first but its supply is limited. Ammonium production within tubular cells eliminates H+ and produces an HCO3- that is reabsorbed
___ ___ ___ (NAE) should remove all nonvolatile acid. What are the three components or forms excreted?
free H+, HPO4-; and NH4+
What does urine contain?
both titratable acids (H+ and HPO4-) and NH4+.
T/F. H+ and HPO4- are not titratable (pKa ~9), however NH4+ can be measured by titration with a base to a pH=7.4.
False, NH4+ is not titratable (pKa ~9), however H+ and HPO4- can be measured by titration with a base to a pH=7.4.
T/F. The kidney regulates the acidity of the urine by regulating HCO3- reabsorption. Under normal conditions, the kidney excretes acid equal to the nonvolatile load and replenishes the HCO3- lost due to neutralizing the nonvolatile acids.
True.
What are the three options for renal regulation of body pH that will produce urine with different pH?
- decrease body pH by not reabsorbing all HCO3- to produce an alkaline urine and acidifies body fluids
- no effect on body pH by reabsorbing all HCO3- (not common)
- increase body pH by reabsorbing all and producing more HCO3- to produce an acidic urine and alkalinizes body fluids (most common)
___ is not directly transported from tubular fluid into the blood so its production and reabsorption results in ___ secretion.
HCO3-; H+
Bicarbonate reabsorption begins in the ___ ___ and ___% of filtered HCO3- is reabsorbed here. How?
proximal tubule; 80
- CA activity in the tubular epithelium produces H+ and HCO3-.
- H+ is secreted via Na+/H+ antiporter. There is also the H+ ATPase pumps (apical) and H+/K+ ATPase pumps operating to secrete H+
- HCO3- is transported/reabsorbed across the basolateral membrane
T/F. Some HCO3- is reabsorbed in the thick ascending limb of the loop of Henle in a manner similar to the mechanism used in the proximal tubule.
True.
T/F. In the late distal tubule, and the collecting duct, CA activity in the tubular epithelium produces H+ and HCO3-
False, In the late distal tubule, and the collecting duct, CA activity in the INTERCALATED CELLS produces H+ and HCO3-.
CA is found in tubular epithelium of the proximal tubule
How is secreted H+ buffered in the distal tubule or collecting duct?
by HCO3-, HPO4-; or ammonia (NH3)
A less common type of ___ ___ reverses the position of the H+ and HCO3- transporters to the ___ and ___ membranes, respectively. These cells ___ H+ and ___ HCO3-.
intercalated cell; basolateral; apical; reabsorb; secrete
activity of this cell type is normally very low
If the body is alkaline, what does the kidney do?
it produces alkaline urine which requires incomplete reabsorption of HCO3- by not neutralizing all the HCO3- that is in the tubular fluid
Cells in the ___ tubule can detect intracellular pH and can alter ___ activity accordingly.
proximal; CA
increase pH - decrease CA activity, not reabsorbing HCO3- therefore more excreted
decreased pH - increase CA activity, more HCO3- reabsorbed and less excreted.
If the body is acidic, use ___ as an additional buffer to increase excretion of ___.
phosphate (HPO4-); H+
After all the HCO3- has been reabsorbed and HPO4- is depleted, what does the kidney do?
it will produce ammonium as a third buffer to increase the amount of H+ that can be excreted.
Note - it is important to keep NH4+ from entering body where it would be converted to urea and produce H+ as a result
NH4+ is produced in the ___ tubule by metabolism of ___. The NH4+ that is produced is transported into the tubular fluid and the ___ moves into blood.
proximal; glutamine; HCO3-
How is the production of NH4+ produced in the proximal tubular cells regulated?
by systemic pH. Acidosis upregulates synthesis of enzymes for glutamine metabolism, but not that this takes time (as does all protein synthesis). This causes a drop in pH and stimulates reactions to produce more NH4+
More NH4+ can be added to the urine by ___ ___.
diffusion trapping
T/F. Much of the NH4+ leaving the proximal tubule is reabsorbed by the descending limb of the loop of Henle.
False, Much of the NH4+ leaving the proximal tubule is reabsorbed by the ASCENDING limb of the loop of Henle.
NH4+ substitutes for ___ in the Na+/K+/Cl- symporter and enters the ___ fluid in the ___ where it is in equilbrium with NH3.
K+; interstitial; medulla
Because it is a ___ molecule, NH4+ is “trapped” in the ___ fluid but NH3 (being ___) can diffuse into the lumen of nearby collecting ducts.
polar; interstitial; nonpolar
T/F. Because there is excess H+ in fluid, NH3 in lumen is protonated to NH4+, which is once again trapped and gets eliminated with the urine.
True.
T/F. Respiratory system keeps PCO2 constant (takes care of volatile acids) and the kidneys regulate bicarbonate (takes care of nonvolatile acids).
True.
T/F. The kidneys typically produce an acidic urine.
True.
T/F. Net acid excretion occurs before all filtered bicarbonate is reabsorbed.
False, Net acid excretion occurs AFTER all filtered bicarbonate is reabsorbed.
T/F. Additional H+ must be buffered to remove significant amounts of it.
True.
T/F. New bicarbonate can be produced in the distal tubule by the production of NH4+ from alanine.
False, New bicarbonate can be produced in the PROXIMAL tubule by the production of NH4+ from GLUTAMINE.
T/F. NH4+ produced in the proximal tubule facilitates H+ excretion in the collecting duct as a consequence of diffusion trapping.
True.
What condition has a low pH due to CO2 buildup in the lungs due to impaired pulmonary function? How does the kidney compensate?
respiratory acidosis
renal produces new HCO3- to increase reabsorption of HCO3-
What condition has a high pH due to low PCO2 in blood due to hyperventilation, anxiety, altitude, fever or drugs? How does the kidney compensate?
respiratory alkalosis
excrete HCO3-
T/F. Metabolic acidosis and alkalosis both involve CO2.
False, they have nothing to do with CO2
Metabolic ___ occurs with low pH due to low HCO3- due to diabetic ketosis, diarrhea, and renal failure. How does the respiratory and renal systems respond?
acidosis
respiratory: hyperventilate to decrease PCO2, trying to blow off CO2
renal: produce new HCO3-
Metabolic ___ has a high pH due to excess HCO3- due to vomiting, antacids, and hemorrhage. How does the respiratory and renal systems compensate?
alkalosis
respiratory: hypoventilate to increase PCO2 in the blood to maintain the pH
renal: excrete HCO3-
What three places and in what capacity is calcium found in the body?
- intracellular fluid (1%)
- extracellular fluid (0.1%) - a little more that 1/2 of ECF calcium is free or complexed with anions, and therefore, can be filtered in the glomerulus
- bone (99%)
T/F. Calcium (and phosphate) are important for many cellular processes and are regulated by renal and digestive systems so that gastrointestinal absorption is balanced by renal excretion.
true
Why is it important to regulate calcium?
hypocalcemia increases excitability of neural and muscle tissues (tetany) - decrease Ca2+ = decrease threshold of channels
hypercalcemia can cause cardiac arrhythmia and disorientation that can lead to death - harder to open voltage gated Na+ channels
A ___ in plasma pH will increase the amount of free ___ which can be filtered and excreted, so alkalosis can lead to ___.
decrease; Ca2+; hypocalcemia
Calcium is regulated by ___ hormones all of which are regulated by a ___ ___ ___ found in plasma membrane of what cells?
three; calcium sensing receptor (CaSR)
- parathyroid gland
- thyroid parafollicular cells
- cells of the proximal tubule
The parathyroid hormone is released in response to ___. What does it do?
hypocalcemia
- increases bone resorption (liberate Ca2+)
- increases renal Ca2+ reabsorption
- stimulates calcitriol production
___ (___)’s metabolism is stimulated by hypocalcemia and/or hypophosphatemia. What does it do?
Calcitriol (1,25 dihydroxycitamin D)
- stimulates active transport mechanism for Ca2+ absorption in the small intestine
- facilitates action of PTH and increases renal Ca2+ transport
When is calcitonin released? What does it do?
It is released in response to hypercalcemia
increases bone deposition
Describe where are how calcium is reabsorbed in the nephron.
- proximal tubule - by paracellular transport/solvent drag (70%)
- thick ascending limb - transcellular and paracellular transport by paracellular NOT solvent drag (20%)
- distal tubule by transcellular reabsorption, which is regulated because expression of Ca2+ transporters is regulated by PTH. If no PTH, there will be no activated channels to excrete Ca2+.
- collecting duct - not involved in Ca2+ reabsorption
