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Physiology - BAM > Final: Lecture 19 > Flashcards

Final: Lecture 19 Flashcards

0
Q

What is the Venous blood pH range?

A

•7.35-7.45

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1
Q

The Arterial blood pH range is what?

A

•7.37-7.44

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2
Q

Bicarbonate Buffer System

A
  • Consists of a weak acid (H2CO3) and bicarbonate salt (NaHCO3)
  • Addition of a strong acid leads to formation of a weak acid
  • Addition of a strong base leads to formation of a weak base
  • Increased levels of HCO3 excreted by the kidneys, net result tendency for CO2 levels in blood to decrease
  • Decreased CO2 levels decrease respiration rate
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3
Q

Henderson-Hasselbalch Equation

A
  • pH=pKa + log[A-]/[HA]
  • pKa for bicarbonate buffer system = 6.1
  • Measured via pCO2 (partial pressure) and multiplied by solubility coefficient of CO2 (.03mmol/mmHg)
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4
Q

Bicarbonate concentration is regulated mainly by the _______?

A

•Kidneys**

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5
Q

pCO2 is controlled by rate of ________?

A

•Respiration**

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6
Q

What is the most important EXTRACELLULAR buffer system?

A

•Bicarbonate Buffer System*

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7
Q

Metabolic acid-base disorders result from primary change in what?

A
  • Bicarbonate concentration in extracellular fluid*
  • Metabolic acidosis: decrease HCO3 (Increase H+)
  • Metabolic alkalosis: Increase HCO3 (decrease H+)
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8
Q

Respiratory acid-base disorders result from primary change in?

A
  • pCO2*
  • Respiratory acidosis: Increase pCO2
  • Respiratory alkalosis: decrease pCO2
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9
Q

Phosphate Buffer System

A
  • Plays major role in buffering renal tubular fluid and intracellular fluids
  • Main elements: H2PO4 and HPO4
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10
Q

What are the two reasons for the importance of the Phosphate buffer system in kidney tubular fluids?

A
  1. Usually becomes greatly concentrated in the tubules

2. Lower pH of the tubular fluid brings the operating ranges of the buffer closer to the pK of the buffer system

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11
Q

Primary method for removing nonvolatile acids (don’t vaporize) is through?

A
  • Renal excretion
  • Almost all bicarbonate is reabsorbed, but it must react with secreted H+ ions to from carbonic acid before it can be reabsorbed
  • 4320 mEq of H+ must be secreted to reabsorb 4320 mEq of filtered bicarbonate
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12
Q

Where in the kidney tubules does H+ ions secretion and bicarbonate reabsorption occur?

A
  • H+ secretion via secondary active transport (coupled with Na transport) occurs in almost all parts of the tubules except the descending and ascending thin limbs of loop of Henle
  • Primary active H+ secretin begins in the late distal tubules in intercalated cells and involves H-transporting ATPase
  • About 80-90% of bicarbonate reabsorption occurs in the Proximal Tubule
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13
Q

Describe the mechanism by which bicarbonate ion is reabsorbed.

A
  • Initiated by a reaction in the tubules between bicarbonate ion filtered at the glomerulus and H+ ion secreted by tubular cells
  • Results in formation of carbonic acid, which then dissociated into CO2 and water
  • CO2 diffuses into tubular cells where it recombines with H2O to generate new carbonic acid molecule then dissociated to form bicarbonate ion and H+ ion
  • Bicarbonate then diffuses through the basolateral membrane into the interstitial fluid and then into blood
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14
Q

What role is played by carbonic anhydrase?

A

•Carbonic acid is necessary fro the formation of carbonic acid from carbon dioxide and water

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15
Q

Explain why the bicarbonate ion returned to the extracellular fluid is not the same as that filtered into the tubular lumen?

A
  • Bicarbonate taken up by pericapillary tubules is formed from dissociation of carbonic acid into H+ and bicarbonate ion
  • This carbonic acid is formed when CO2 is taken up the tubular cells and combined with H2O under the influence of carbonic anhydrase
16
Q

Explain how bicarbonate ion is normally titrated against H+ ion.

A

•Normally each time a H+ ion is formed int he tubular epithelial cells, a bicarbonate ion is also formed and released back into the blood

17
Q

In metabolic acidosis new bicarbonate ion is _______ to the extracellular fluid.

A

•Added

18
Q

In metabolic alkalosis, bicarbonate ions are _________ from extracellular fluid by renal excretion.

A

•Removed

19
Q

Active transport resulting in H+ ion secretion is carried out by __________. Where are these cells located specifically in the tubules?

A
  • Intercalated cells

* Found in the late distal renal tubules

20
Q

Describe the 2-step process of H+ secretion in intercalated cells.

A
  1. Dissolved CO2 in intercalated cells combines with water to form carbonic acid
  2. Carbonic acids then dissociates into bicarbonate, which is rapidly reabsorbed into the blood, and H+ ion, which is secreted into the tubular lumen by means of H-ATPase transporter
21
Q

How is H+ secretion carried out in the proximal tubule?

A
  • Occurs via secondary Na-H+ counter-transport
  • Located on the apical membranes of renal epithelial cells
  • Na-K+ ATPase exchangers are found on the basal membranes
22
Q

What is the lower limit of pH that can be achieved in normal kidneys?

A

•4.5*

23
Q

If H+ ions are combining with other buffers in tubular lumen, the excess bicarbonate ion is available to be returned to blood. Referred to as?

A

•New bicarbonate ion*

24
Q

What limits the amount of free H+ ions that can be excreted?

A
  • Only small amount of excess H+ an be excreted in ionic form in urine b/c minimal urine pH is 4.5
  • To excrete the 80 mEq of nonvolatile acid formed from metabolism per day, 2667 L of urine would have to be excreted if all excess H+ remained free in solution
25
Q

What buffers are important in allowing larger amounts of H+ ions to be excreted?

A
  • phosphate buffer system

* Ammonia buffer system

26
Q

How does the excretion of excess H+ lead to formation of new bicarbonate ions?

A
  • H+ eliminated through binding with phosphate or ammonia ions.
  • Bicarbonate formed when CO2 and water combines in the tubular cells and then dissociates into H+ and bicarbonate can be returned to extracellular fluid and blood
27
Q

Alkalosis

A
  • Reduction in extracellular fluid H+ concentration
  • Kidneys fail to reabsorb all the filtered bicarbonate
  • Same thing as adding H+, extracellular pH returns to normal
28
Q

Acidosis

A
  • Increase in extracellular H+
  • Kidneys reabsorb all filtered bicarbonate and produce new bicarbonate ion.
  • Added back to extracellular fluid, pH returns to normal
29
Q

Transport of carbonic acid across the basolateral membrane is facilitated by?

A
  • Na/bicarbonate co-transporter in proximal tubules

* Cl/bicarbonate exchange in late segments of proximal tubule, thick ascending, and collecting tubule/ducts

Physiology - BAM (7 decks)

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