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Human Physiology > Acid-base Balance and Ca2+ Homeostasis > Flashcards

Acid-base Balance and Ca2+ Homeostasis Flashcards

1
Q

If the pH is less than ___ or greater than ___ life cannot be sustained because proteins will stop working.

A

6.8; 7.8

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2
Q

Why is too much acid the greatest concern?

A

because the body takes in (and/or produces) more acid than base

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3
Q

What two forms of acid should we be concerned about?

A
  1. 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)
  2. nonvolatile acids - arise from metabolism or the diet (phosporic, latic, and sulfuric acids and ketones)
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4
Q

Nonvolatile acids must be neutralized with ___, are regulated by the ___ system, and neutralization requires continual replenishment of ___

A

HCO3-; renal; HCO3-

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5
Q

The amount of acid in the urine should equal the nonvolatile acid load. How does the kidney accomplish this?

A

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.

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6
Q

How do buffers function in the urine?

A

They bind to excess of free H+ to increase acid carried in urine without decreasing pH

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7
Q

The kidney can produce ___ to act as a buffer, but it also adds ___ and ___ to the filtrate to increase the amount of H+ excreted

A

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

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8
Q

___ ___ ___ (NAE) should remove all nonvolatile acid. What are the three components or forms excreted?

A

free H+, HPO4-; and NH4+

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9
Q

What does urine contain?

A

both titratable acids (H+ and HPO4-) and NH4+.

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10
Q

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.

A

False, NH4+ is not titratable (pKa ~9), however H+ and HPO4- can be measured by titration with a base to a pH=7.4.

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11
Q

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.

A

True.

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12
Q

What are the three options for renal regulation of body pH that will produce urine with different pH?

A
  1. decrease body pH by not reabsorbing all HCO3- to produce an alkaline urine and acidifies body fluids
  2. no effect on body pH by reabsorbing all HCO3- (not common)
  3. increase body pH by reabsorbing all and producing more HCO3- to produce an acidic urine and alkalinizes body fluids (most common)
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13
Q

___ is not directly transported from tubular fluid into the blood so its production and reabsorption results in ___ secretion.

A

HCO3-; H+

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14
Q

Bicarbonate reabsorption begins in the ___ ___ and ___% of filtered HCO3- is reabsorbed here. How?

A

proximal tubule; 80

  1. CA activity in the tubular epithelium produces H+ and HCO3-.
  2. H+ is secreted via Na+/H+ antiporter. There is also the H+ ATPase pumps (apical) and H+/K+ ATPase pumps operating to secrete H+
  3. HCO3- is transported/reabsorbed across the basolateral membrane
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15
Q

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.

A

True.

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16
Q

T/F. In the late distal tubule, and the collecting duct, CA activity in the tubular epithelium produces H+ and HCO3-

A

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

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17
Q

How is secreted H+ buffered in the distal tubule or collecting duct?

A

by HCO3-, HPO4-; or ammonia (NH3)

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18
Q

A less common type of ___ ___ reverses the position of the H+ and HCO3- transporters to the ___ and ___ membranes, respectively. These cells ___ H+ and ___ HCO3-.

A

intercalated cell; basolateral; apical; reabsorb; secrete

activity of this cell type is normally very low

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19
Q

If the body is alkaline, what does the kidney do?

A

it produces alkaline urine which requires incomplete reabsorption of HCO3- by not neutralizing all the HCO3- that is in the tubular fluid

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20
Q

Cells in the ___ tubule can detect intracellular pH and can alter ___ activity accordingly.

A

proximal; CA

increase pH - decrease CA activity, not reabsorbing HCO3- therefore more excreted

decreased pH - increase CA activity, more HCO3- reabsorbed and less excreted.

21
Q

If the body is acidic, use ___ as an additional buffer to increase excretion of ___.

A

phosphate (HPO4-); H+

22
Q

After all the HCO3- has been reabsorbed and HPO4- is depleted, what does the kidney do?

A

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

23
Q

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.

A

proximal; glutamine; HCO3-

24
Q

How is the production of NH4+ produced in the proximal tubular cells regulated?

A

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+

25
Q

More NH4+ can be added to the urine by ___ ___.

A

diffusion trapping

26
Q

T/F. Much of the NH4+ leaving the proximal tubule is reabsorbed by the descending limb of the loop of Henle.

A

False, Much of the NH4+ leaving the proximal tubule is reabsorbed by the ASCENDING limb of the loop of Henle.

27
Q

NH4+ substitutes for ___ in the Na+/K+/Cl- symporter and enters the ___ fluid in the ___ where it is in equilbrium with NH3.

A

K+; interstitial; medulla

28
Q

Because it is a ___ molecule, NH4+ is “trapped” in the ___ fluid but NH3 (being ___) can diffuse into the lumen of nearby collecting ducts.

A

polar; interstitial; nonpolar

29
Q

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.

A

True.

30
Q

T/F. Respiratory system keeps PCO2 constant (takes care of volatile acids) and the kidneys regulate bicarbonate (takes care of nonvolatile acids).

A

True.

31
Q

T/F. The kidneys typically produce an acidic urine.

A

True.

32
Q

T/F. Net acid excretion occurs before all filtered bicarbonate is reabsorbed.

A

False, Net acid excretion occurs AFTER all filtered bicarbonate is reabsorbed.

33
Q

T/F. Additional H+ must be buffered to remove significant amounts of it.

A

True.

34
Q

T/F. New bicarbonate can be produced in the distal tubule by the production of NH4+ from alanine.

A

False, New bicarbonate can be produced in the PROXIMAL tubule by the production of NH4+ from GLUTAMINE.

35
Q

T/F. NH4+ produced in the proximal tubule facilitates H+ excretion in the collecting duct as a consequence of diffusion trapping.

A

True.

36
Q

What condition has a low pH due to CO2 buildup in the lungs due to impaired pulmonary function? How does the kidney compensate?

A

respiratory acidosis

renal produces new HCO3- to increase reabsorption of HCO3-

37
Q

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?

A

respiratory alkalosis

excrete HCO3-

38
Q

T/F. Metabolic acidosis and alkalosis both involve CO2.

A

False, they have nothing to do with CO2

39
Q

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?

A

acidosis

respiratory: hyperventilate to decrease PCO2, trying to blow off CO2
renal: produce new HCO3-

40
Q

Metabolic ___ has a high pH due to excess HCO3- due to vomiting, antacids, and hemorrhage. How does the respiratory and renal systems compensate?

A

alkalosis

respiratory: hypoventilate to increase PCO2 in the blood to maintain the pH
renal: excrete HCO3-

41
Q

What three places and in what capacity is calcium found in the body?

A
  1. intracellular fluid (1%)
  2. 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
  3. bone (99%)
42
Q

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.

A

true

43
Q

Why is it important to regulate calcium?

A

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

44
Q

A ___ in plasma pH will increase the amount of free ___ which can be filtered and excreted, so alkalosis can lead to ___.

A

decrease; Ca2+; hypocalcemia

45
Q

Calcium is regulated by ___ hormones all of which are regulated by a ___ ___ ___ found in plasma membrane of what cells?

A

three; calcium sensing receptor (CaSR)

  1. parathyroid gland
  2. thyroid parafollicular cells
  3. cells of the proximal tubule
46
Q

The parathyroid hormone is released in response to ___. What does it do?

A

hypocalcemia

  1. increases bone resorption (liberate Ca2+)
  2. increases renal Ca2+ reabsorption
  3. stimulates calcitriol production
47
Q

___ (___)’s metabolism is stimulated by hypocalcemia and/or hypophosphatemia. What does it do?

A

Calcitriol (1,25 dihydroxycitamin D)

  1. stimulates active transport mechanism for Ca2+ absorption in the small intestine
  2. facilitates action of PTH and increases renal Ca2+ transport
48
Q

When is calcitonin released? What does it do?

A

It is released in response to hypercalcemia

increases bone deposition

49
Q

Describe where are how calcium is reabsorbed in the nephron.

A
  1. proximal tubule - by paracellular transport/solvent drag (70%)
  2. thick ascending limb - transcellular and paracellular transport by paracellular NOT solvent drag (20%)
  3. 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+.
  4. collecting duct - not involved in Ca2+ reabsorption

Human Physiology (22 decks)

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