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Digestion and Excretion > Proximal Tubular reabsorption and secretion > Flashcards

Proximal Tubular reabsorption and secretion Flashcards

1
Q

Where is the PCT mainly found?

A

Cortex

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2
Q

What increases surface area for reabsorption of the proximal tubule?

A

Microvilli on luminal surface

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3
Q

What does the proximal tubule reabsorb?

A

Na+
Cl-
Glucose
Protein/AA
HCO3-
Water

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4
Q

What is paracellular reabsorption?

A

Leakiness of tight junctions

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5
Q

What is transcellular reabsorption?

A

Dependent on presence of transporters

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6
Q

How do solutes move from the lumen to the interstitial fluid?

A

Concentration gradients
Electrochemical gradients
Na+K+ ATPase pump

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7
Q

How do solutes move from the interstitial fluid to vasculature?

A

Passive diffusion
Oncotic pressure

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8
Q

How is Na+ cleared?

A

Freely filtered, actively reabsorbed, not secreted

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9
Q

How is Na+ reabsorbed in the first half of the PCT?

A

With HCO3- and glucose

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10
Q

How is Na+ reabsorbed in the second half of the PCT?

A

With Cl- and glucose

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11
Q

Where is Na+K+ATPase pump restricted to?

A

Basolateral side of the cell

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12
Q

How does Na+ enter the cell from the lumen in the first half of PCT?

A

Via the Na+-H+ antiporter

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13
Q

How does Na+ enter the ISF from the cell in the first half of PCT?

A

Na+/K+ATPase pump
Na+-HCO3- symporter

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14
Q

How is the lumen negative potential difference across cells in early PCT created?

A

By Na+ cotransporters - bring net +ve charge into cell leaving -ve charge behind

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15
Q

How is glucose reabsorbed in PCT?

A

Na+ dependent - no transepithelial or electrochemical gradient present for glucose

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16
Q

How does glucose enter the cell from the lumen?

A

SLGT2 symporters

17
Q

How does glucose enter the ISF from the cell?

A

Glucose uniporters (GLUT2)

18
Q

Why does tubular Cl- fluid rise along length of PCT?

A

More water being reabsorbed than Cl-
Preferential reabsorption of Na+ with HCO3-

19
Q

How does Cl- enter the cell from the lumen in the second half of PCT?

A

Cl- anion antiporter

20
Q

How does Cl- enter the ISF from the cell in the second half of the PCT?

A

K+-Cl_ symporter

21
Q

What are the glucose transporters in the second half of the PCT?

A

SGLT1
GLUT1

22
Q

How is water reabsorbed in the PCT?

A

Aquaporin water channels on apical and basolateral membrane

23
Q

What is solvent drag in the PCT?

A

Osmotic water flow results in reabsorption of some solutes, eg. K+, Ca2+ and Mg2+, by solvent drag along paracellular routes

24
Q

What does the PT secrete?

A

Organic anions and cations (metabolism products)
Exogeneous organic compounds (drugs and toxic chemicals)

25
Q

Where do secreted substances originate from?

A

Crossing epithelial layer from renal interstitium
Synthesis within epithelial cells

26
Q

Does paracellular secretion occur?

A

No

27
Q

What is tubular secretion coupled to?

A

Reabsorption of Na+

28
Q

Where does tubular secretion move substances from?

A

Peritubular capillaries into tubular lumen

29
Q

How are anions moved into the cell from the ISF?

A

Basolateral OAT antiporters move anions in exchange for endogenous dicarboxylic acid eg. alpha ketoglutarate

30
Q

How do alpha ketoglutarate move into the cell?

A

Via sodium dicarboxylate symporters (NaDC3)

31
Q

How are anions transported across apical membrane?

A

By OAT and MRP proteins along conc. gradients

32
Q

What can cause gout?

A

Elevated plasma conc. of urate

33
Q

What is apical cation transport fuelled by?

A

Na+/K+ATPase pump

34
Q

What drives H+ out of the cell into the lumen?

A

Sodium gradient by NHE3

35
Q

How are small cations moved out of the cell into the lumen?

A

Apical OCTN proteins in exchange for H+

36
Q

How are larger cations transported out of the cell?

A

Via MDR1 ATPase transporter on apical membrane

37
Q

How are cations transported across basolateral membrane?

A

Passive diffusion
Different OCT proteins along conc. gradients

38
Q

What is the transport maximum of a system?

A

Amount of solute delivered to the tubule per minute that just saturates its transport process

39
Q

What is the Tm for glucose?

A

380mg/min

Digestion and Excretion (22 decks)

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