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VET 409: Renal > Tubular Reabsorption & Secretion > Flashcards

Tubular Reabsorption & Secretion Flashcards

1
Q

steps of solute/water reabsorption

A

tubule –> interstitium –> capillaries

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2
Q

is reabsorption the same across the entire nephron

A

no - spatial; different components get reabsorbed at different points along the tubule

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3
Q

types of transport

A

paracellular (between cells)
transcellular (through cells)

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4
Q

what does it mean that transporter mediated transport is saturable?

A

reabsorption is dependent on the number of available transporters - will reach a maximum rate when all transporters occupied

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5
Q

is filtration saturable

A

NO - filtration only depends on GFR and plasma concentration

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6
Q

what does it mean if there is no solute detected in the urine

A

filtration of solute = reabsorption of solute

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7
Q

does reabsorption increase with filtration

A

yes - reabsorption and filtration will increase at the same rate until plasma concentration of the solute gets too high and all transporters are occupied (causes filtration to continue increasing while reabsorption plateaus)

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8
Q

what does reabsorption depend on

A

plasma concentration
GFR
Tm

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9
Q

what is transport maximum (Tm)

A

the maximum rate of reabsorption (mass of solute that can be transported per minute)

appears as a constant Y value (horizontal line)

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10
Q

what is renal threshold

A

the plasma concentration of a substance at which it begins to appear in urine (when reabsorption < filtration)

appears as a constant X value (vertical line)

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11
Q

how does decreasing GFR affect Tm and renal threshold

A
  • NO EFFECT on Tm
  • increases renal threshold (more time available to clear transporters)
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12
Q

what are the starling forces entering peritubular capillaries

A

efferent arterioles: low hydrostatic and high oncotic –> favors reabsorption

peritubular cap: high hydrostatic pressure of interstitium and oncotic pressure of capillaries; low hydrostatic pressure of capillaries and oncotic pressure of interstitium

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13
Q

what transport mechanisms are in the proximal convoluted tubule

A

Na/K ATPase
Na/Glu cotransporter
Na/H antiporter
Na/PO4 cotransporter
Paracellular Cl, Ca, Mg
Urea transporters
Aquaporins

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14
Q

what is the osmolarity of filtrate going through the PCT

A

isotonic - equal amounts of solute and water reabsorbed

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15
Q

what transport mechanisms are in the descending loop of henle

A

Aquaporins
Urea transporters - secretes urea INTO filtrate from interstitium

IMPERMEABLE to NaCl

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16
Q

what is the osmolarity of the filtrate going through the descending loop

A

osmolarity INCREASES down descending loop

urea concentration INCREASES down descending loop

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17
Q

what transport mechanisms are in the ascending loop of henle

A

Na/K ATPase
NKCC (Na/K/2Cl) cotransporter
Paracellular Ca, Mg

IMPERMEABLE to water

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18
Q

what is the osmolarity of the filtrate as it goes through the ascending loop

A

osmolarity DECREASES up ascending loop

19
Q

what transport mechanisms are in the distal convoluted tubule

A

Na/K ATPase
TRPV5 (Ca from lumen –> cytosol)
NCX1 (Ca reabsorption)

Early DCT:
- NCC (Na/Cl cotransporter)
- ROMK (K excretion)

Late DCT:
- ENaC (Na transporter)
- ROMK (K excretion)
- some NCC

20
Q

what is the osmolarity of the filtrate going through the DCT

A

hypo-osmotic filtrate enters but DCT is load sensitive

if filtrate Na concentration is HIGH - will increase reabsorption
if filtrate Na concentration is LOW - will decrease reabsorption

21
Q

what transport mechanisms are used in the collecting ducts

A

Na/K ATPase
ENaC
ROMK
Urea transporters (ADH dependent) - reabsorbs out of filtrate ONLY when ADH is present

22
Q

is reabsorption rate constant regardless of changes in GFR

A

NO - reabsorption rate changes with GFR to prevent excess losses

dependent on starling forces in peritubular capillaries

23
Q

antidiuretic hormone action

A

ADH responds to high NaCl or low BP

produced in hypothalamus and secreted by pituitary

causes translocation of aquaporins and urea transporters to CD membrane

effect: increases water and urea reabsorption

24
Q

how does ADH secretion vary based on hydration state

A

dehydrated: increase ADH
hydrated: decrease ADH

25
Q

how does urea contribute to medullary hyperosmolarity

A

urea concentration in the filtrate increases from PCT –> DCT

when ADH is present: urea gets reabsorbed which decreases osmolarity of the tubule, leading to increased water reabsorption

26
Q

what is countercurrent multiplication

A

creates and maintains medullary interstitial osmotic gradient

descending LoH: interstitium is hyperosmotic –> pulls water out of filtrate –> causes filtrate osmolarity to increase down descending loop

ascending LoH: hyperosmotic filtrate causes NaCl reabsorption into interstitium –> decreases filtrate osmolarity as it enters DCT

effect of differences in Na and water concentration get multiplied as fluid moves counter currently

27
Q

RAAS signal

A

low NaCl and low BP/ECFV

sensed by baroreceptors, macula densa cells, and sympathetic nervous system

28
Q

RAAS mechanism of action

A

sensors signal to JG cells –> increase renin secretion

renin cleaves angiotensinogen –> ANG I

ACE cleaves ANG I –> ANG II

ANG II –> binds to AT1 receptors on targets

29
Q

angiotensin II targets

A
  • efferent > afferent arterioles
  • Na/K ATPase
  • NCC transporter
  • ROMK transporter
  • adrenal gland
30
Q

angiotensin II effects

A
  • vasoconstriction (dec. RBF/GFR/P(GC)/NFP)
  • increased Na reabsorption
  • increased aldosterone secretion
31
Q

aldosterone targets

A
  • NCC
  • ENaC
  • ROMK
32
Q

aldosterone effects

A
  • increase Na reabsorption
  • increase K excretion
33
Q

what is the main nephron region targeted by aldosterone

A

collecting ducts

34
Q

what are the different cell types in collecting ducts and why are there different types?

A

principal cells, intercalated cells

different types allow for separate regulation of Na reabsorption and K excretion / acid/base balance

35
Q

principal cells

A

Na and K regulation

36
Q

intercalated cells

A

H+ secretion and acid/base balance

37
Q

where is the main nephron region of PO4 reabsorption

A

proximal convoluted tubule

Na/PO4 cotransporter
(driven by Na/K ATPase)

38
Q

what stimulates PO4 reabsorption

A

calcitriol
low dietary PO4

39
Q

what inhibits PO4 reabsorption

A

PTH
FGF-23
high dietary PO4

40
Q

where is the main site of Ca reabsorption

A

proximal convoluted tubule

paracellular transport - regulated by CaSR/claudins and driven by electrical gradients

41
Q

what stimulates Ca reabsorption

A

PTH
calcitriol
hypocalcemia
thiazide diuretics

42
Q

what inhibits Ca reabsorption

A

hypercalcemia
furosemide

43
Q

where is the main site of Mg reabsorption

A

thick ascending LoH

paracellular - regulated by CaSR/claudins and driven by electrochemical gradients from NKCC2

VET 409: Renal (21 decks)

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