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PHYSIOLOGY II > Lecture 4: Tubular Transport > Flashcards

Lecture 4: Tubular Transport Flashcards

1
Q

why is the rate of reabsorption and secretion of substances variable throughout the tubular system

A

b/c of differences in permeability and transporters / channels

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2
Q

what facilitates transport across tubular epithelial cells

A

an enlarged surface area on the apical side (brush border) and basolateral side (micropedici)

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3
Q

epithelial cells are connected to eachother by _____ ?

A

tight junctions. they limit paracellular transport

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4
Q

what portion of the tubule system reabsorbs 80% of water

A

Proximal tubule and descending limb of the LoH

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5
Q

what part of the tubular system has thick ascending limbs and reabsorbs 30% of the NaCl filtered by the glomerulus

A

Ascending limb of the LoH and early distal tubule

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6
Q

how do NaCl and K enter the cell

A

via NKCC-2

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7
Q

what is the function of the distal convoluted tubule

A

reabsorbing NaCl via NCC

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8
Q

what does the collecting duct have a role in

A

adjusting the final urine composition

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9
Q

where does glucose and amino acid reabsorption occur

A

the proximal tubule

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10
Q

what transporters are present in the apical membrane of the PT

A

sodium dependent transporters (SGLT1 & SGLT2) for glucose and EAAT3, SIT1 for amino acids

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11
Q

what type of transport is utilized in the reabsorption of glucose from the lumen of the nephron back into the cells of the PT

A

secondary active transport, linked to sodium ions

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12
Q

Once back inside the PT cells how does glucose diffuse into the interstitial space

A

via facilitated diffusion proteins located in the basal membrane of PT cells

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13
Q

what drives small glucose molecules to diffuse into peritubular capillaries

A

protein oncotic pressure

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14
Q

what is tubular maximum (mg/min)

A

the max rate of reabsorption that is reached when all membrane transport proteins are saturated

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15
Q

below tubular maximum, what happens to the filtered load

A

it is all reabsorbed

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16
Q

what happens to the filtered load when TM is exceeded

A

it is excreted

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17
Q

where are tubular maximum primarily found

A

PT

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18
Q

where does the reabsorption of bicarbonate take place

A

PT

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19
Q

CO2 can move into epithelial cells via what methods

A

via transmembrane diffusion or AQP1

20
Q

where are sodium dependent transporters (NHE3) that remove protons during the reabsorption of bicarbonate found

A

in the apical membrane of the proximal tubule

21
Q

what transporters are present in the proximal tubule that help effectively reabsorb glucose?

A

SGLT1

22
Q

what is the difference b/w carrier-mediated transport of glucose vs simple diffusion of glucose

A

carrier-mediated transport can max out (b/c it is sodium-dependent) whereas transport by simple diffusion doesn’t really max out, but is somewhat dependent on available SA

23
Q

why is glucose usually not present in urine

A

b/c transport rate is not maxed out
– as long as max rate (TM) isn’t reached, glucose is able to be fully reabsorbed

24
Q

what happens when tubular max is reached

A

glucose appears in urine

25
Q

since bicarbonate cannot be directly absorbed through the apical membrane, what is required to convert it into CO2 (a form that can cross membrane)

A

carbonic anhydrase

26
Q

unlike at the apical membrane, bicarbonate can be directly transferred from inside the cell across the basolateral membrane by what transporter

A

Na/K ATPase pump

27
Q

where does reabsorption of bicarbonate occur

A

proximal tubule

28
Q

the reabsorption of bicarbonate via the Na/H exchanger (NHE3) depends on the activity of what enzyme

A

carbonic anhydrase

29
Q

the reabsorption of sodium occurs in what parts of the tubule system

A

PT
LoH
DCT
CD

30
Q

what regulates the secretion of potassium secretion

A

K+ homeostasis

31
Q

where does potassium secretion occur mainly and how

A

in the collecting duct via apical K+ channels (ROMK< BK)

32
Q

where does potassium absorption occur

A

DCT and CD

K is reabsorbed in exchange for H by an ATP dependent pump, the H/K ATPase

33
Q

where does reabsorption of chloride occur and through what mechanisms

A

in all segments of the nephron

  • via paracellular pathway (through tight junctions)
  • via transcellular mechanisms (chloride couples transporters and chloride channels such as pendrin, NCC, NKCC-2)
34
Q

what factors upregulate phosphate transporter expression

A

dietary phosphate deficiency, TH, IGF

35
Q

what factors downregulate phosphate transporter expression

A

PTH (secreted in response to low blood Ca levels)

dietary potassium deficiency, metabolic acidosis, high phosphate diet, estrogen, glucocorticoids

36
Q

where does reabsorption of urea occur and how

A

in the PT and LoH via simple diffusion
in the CD by urea transporter

37
Q

where does urea accumulate

A

in the inner medulla

*establishes high tonicity in the medulla that allows for water reabsorption

38
Q

what limb of the LoH is impermeable to water

A

thick ascending limb

39
Q

the proximal tubule has what transporters for glucose and amino acid uptake

A

SGLT1 and SGLT2 for glucose and EAAT3, SIT1 for amino acids

40
Q

water reabsorption in the collecting duct is dependent on what

A

the presence of vasopressin (ADH) (hormone)

41
Q

what is the method of Na absorption in the PT

A

Na+ dependent solute transporter and Na/H exchanger

42
Q

what is the method of Na absorption in the LoH

A

NKCC-2 co-transporter in the apical membrane

43
Q

what is the method of Na absorption in the DCT

A

NCC co-transporter

44
Q

what is the method of Na absorption in the CD

A

ENac promotes sodium uptake

45
Q

what segments of the tubular system are impermeable to water

A

LoH, TAL, DCT

PHYSIOLOGY II (17 decks)

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