L5 Proximal Tubular Reabsorption and Secretion Flashcards

1
Q

What does the proximal tubule absorb? Percentage of each?

Na+ (_____________________)

Cl- (_____________________)

Glucose (_____________________)

Protein/amino-acids (_____________________)

HCO3 (_____________________)

Water (_____________________)

A

Na+ (⅔ filtered is reabsorbed)

Cl- (⅔ filtered is reabsorbed)

Glucose (virtually all)

Protein/amino-acids (virtually all)

HCO3 (80% filtered is reabsorbed)

Water (absorbed osmotically along with solutes)

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2
Q

________ of all human genes code for transport proteins.

A

5%-10% of all human genes code for transport proteins.

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2
Q

In first half of PCT, Na+ reabsorbed primarily with ____________ and ______________

In second half of PCT, Na+ reabsorbed with ____________ and ________________

A

In first half, Na+ reabsorbed primarily with Bicarbonate (HCO3-) and Glucose

In second half, Na+ reabsorbed with Cl- and Glucose

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3
Q

In the early proximal tubule, there is a _______________________ across the cells created by Na+ cotransporters (bringing net positive charge into the cell and leaving negative charge in the lumen)

A

In the early proximal tubule, there is a lumen-negative potential difference across the cells created by Na+ cotransporters (bringing net positive charge into the cell and leaving negative charge in the lumen)

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4
Q

First Half of PCT
______________ are on the apical membrane and bring in Glucose along Na+ concentration gradient (#?)

_________________ on the basolateral surface allow glucose into the interstitial space

_____________ brings Na+ into the cell and H+ ions from cellular metabolism are secreted in the first half of the PCT

____________ transports bicarbonate from cells of the first half of the PCT into interstitial space

A

SGLT2 Glucose Symporters are on the apical membrane and bring Glucose along Na+ concentration gradient (1 Na+ w/ 1 Glucose)

Glucose Uniporters (GLUT2) on the basolateral surface allow glucose into the interstitial space

Na+/H+ Antiporter (NHE3) brings Na+ into the cell and H+ ions from cellular metabolism are secreted in the first half of the PCT

Na+/HCO3 Symporter (NBC1) transport bicarbonate from cells of the first half of the PCT into interstitial space

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5
Q

Why does the concentration of tubular Cl- along the length of PCT rise?

A

The concentration of tubular Cl- along the length of PCT RISES due to:

  • more water being reabsorbed than Cl
  • preferential reabsorption of Na+ with HCO3-in first half of PCT (NO Cl- Transporters)
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6
Q

Second half of the PCT

Tubular fluid has little ______ and high ______

____________ on the apical membrane bring Glucose along the Na+ concentration gradient into cells (#?)

_________on the basolateral surface allow glucose into the interstitial space

A

The second half of PCT Tubular fluid has little Glucose and high Cl-

SGLT1 Glucose Symporters on the apical membrane bring Glucose along Na+ concentration gradient into cells (2 Na+ w/ 1 Glucose)

Glucose Uniporters (GLUT1) on the basolateral surface allow glucose into the interstitial space

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7
Q

________________________: Antiporter on apical surface of the proximal tubule that secretes organic ANIONs into the tubule lumen

_______________________: ATPase transporter on the apical surface of the proximal tubule that secretes organic ANIONs into the tubule lumen

Example Anion?

A

Organic Anion Transporter (OAT4): Antiporter on apical surface of the proximal tubule that secretes organic ANIONa into the tubule lumen

Multidrug resistance-associated protein (MRP2): ATPase transporter on the apical surface of the proximal tubule that secretes organic ANIONs into the tubule lumen

__Example:_: PAH, Urate

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8
Q

Antiporters on apical surface of the proximal tubule that secrete organic CATIONs into the tubule lumen?

A

Multidrug resistance-associated protein (MRP1)- Large cations

Organic cation transporter (OCTN/OCT)- Small cations

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9
Q

Organic Cation secretion (PCT)

  1. Apical cation transport is fueled by Na+/K+/ATPase pump.
  2. Resulting sodium gradient drives H+ out of the cell via the ____________________.
  3. Apical OCTN proteins move small cations out of the cell in exchange for H+ while larger cations are transported out via _____________ transporter
  4. Cations are transported across basolateral membrane, via passive diffusion or _____________, along concentration gradients.

Example Cation?

A
  1. Apical cation transport is fueled by Na+/K+/ATPase pump.
  2. Resulting sodium gradient drives H+ out of the cell by the Sodium Hydrogen Antiporter (NHE3).
  3. Apical OCTN proteins move small cations out of the cell in exchange for H+. Larger cations transported out via MDR1 ATPase transporter.
  4. Cations are transported across basolateral membrane, via passive diffusion or via OCT 1,2,3, along concentration gradients.

Example: Creatine

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10
Q

________________:amount of solute delivered to the tubule per minute that just saturates its transport process

A

Transfer or Transport Maximum (Tm) ~380mg/min

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11
Q

Co-infusion of ________ w/ penicillin (BOTH ____) reduces penicillin excretion extending its biological half-life.

A

Co-infusion of Hippurates w/ penicillin (BOTH ANIONS) reduces penicillin excretion extending its biological half-life.

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12
Q

Why does elevated plasma levels of one cation (or anion) inhibit secretion of the other?

A

Because organic cations (and anions) compete for the same secretory pathways both reabsorption and secretory transport processes can become saturated i.e. tubular maximum-limited (Tm) systems

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13
Q

____________ is particularly critical for the excretion of anions and cations extensively bound to plasma proteins and not filterable at renal corpuscle

A

PCT secretion is particularly critical for the excretion of anions and cations extensively bound to plasma proteins and not filterable at renal corpuscle

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14
Q

How are most proteins reabsorbed from the urine?

A

Receptor-mediated endocytosis (aka Pinocytosis)

This mechanism reabsorbs virtually all the proteins filtered, and hence the urine is essentially protein free in the healthy kidney

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15
Q

What is Splay with regard to Glucose Titration?

A

Splay of the Excretion curve relative to plasma concentration of glucose is because of nephron heterogeneity; some nephrons can absorb more than others (due to variations in SGLT1 and SGLT2 expression)

16
Q

Renal Threshold vs. Transport Maximum

A

Renal Threshold = upper limit for reabsorption( [Plasma] ≥ 200mg/dL) => Glucosuria when exceeded

Transport maximum (Tm) for glucose, at which increased
the concentration of Plasma does not result in an increase in the reabsorption of glucose ( ~380mg/min)