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urinary system > tubular function > Flashcards

tubular function Flashcards

1
Q

processes that remove and return substances to the blood

A

filtration
reabsorption
secretion

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2
Q

why do you need reabsorption

A

need to keep 99% of ultrafiltrate
move 180L into tubular system - need to get this back
maintain plasma balance, plasma conc and pH

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3
Q

transcellular

A

substances move through the cell

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4
Q

paracellular

A

substances travel through the TJ between the cells

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5
Q

are secretion and reabsorption trans/paracellular

A

both can occur through both pathways

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6
Q

transport of lipophilic molecules

A

lipid soluble
rate only dependant on concentration - linear
protein independent

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7
Q

transport of hydrophilic molecules

A

gated through proteins

rate limited by protein transporters

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8
Q

Kinetics for active movement

A

same as for facilitative transport

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9
Q

direct AT

A

directly coupled to ATP hydrolysis

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10
Q

secondary AT

A

indirectly coupled to ATP hydrolysis

active pumping of Na out of cell creates conc gradient for Na to cotransport something into the cell

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11
Q

water transport

A

through the TJ - not that tight
move to high osmolarity
store aquaporin in cell when don’t want movement
move aqauporins to surface when you do

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12
Q

protein reabsorption

A

proteins are in primary urine - need to reabsorb all
bind to receptor - low specificity, high capacity
when bind = trapped
endocytosed into cell
when low pH in endosome - dissociate from the receptor

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13
Q

transport maxima

A

point where increasing the solute concentration wont mean that you will increase more
when it is exceeded - see solute in urine - 15mmol/l for glucose
also happens for Vit B and C

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14
Q

describe secretion

A

moves substances from peritubular capillaries to tubular lumen
constitutes a pathway into tubule
diffusion/transcellular mediated transport

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15
Q

substances that are secreted

A

most important - H+ and K+

choline, creatinine, penicillin and other drugs

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16
Q

renal tubular acidosis

A

merperchloremic metabolic acidosis
cause impaired growth and hypokalaemia
failure of proton excretion in distal tubules
less acidic urine

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17
Q

bartter syndrome

A 
excessive electrolyte secretion 
antenatal Bartter syndrome: 
premature birth
polyhydramnios 
severe salt loss = renin and ang hypersecretion - water follow salt 
moderate met alkalosis 
hypokalaemia 
because of mutation in Na/K/2Cl - responsible for uptake of 25%
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18
Q

Fanoci syndrome

A

increased secretion of uric acid, glucose, phosphate, bicarb and low molecular weight protein
disease of PCT
associated with renal tubular acidosis = unable to separate protein from receptor because cant acidify endosome
2cl- moved in and 1 H+ out - when mutated the charge gradient increases - more difficult to pump in H+ therefore cabt acidify endosome

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19
Q

percentage of water reaching different points in nephron

A

100% enter = 180L
30% reach descending limb
20% DCT
only 1 or 2L leave = «1 or 10%

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20
Q

where are most of the Na transporters

A

PCT

21
Q

amount of solute reabsorbed in the PCT

A 
60-70% all solute 
100% glucose
65% Na 
90% bicarb 
water and anions follow
22
Q

structure of PCT

A

dense brush border = large SA

a lot of mt

23
Q

structure of descending loop of henle

A

few mt

loose TJ

24
Q

structure of ascending limb

A

lot of mt - because where absorb Na
cuboidal epi
few microvilli

25
Q

structure of DCT

A

a lot of mt

squamous epi

26
Q

structure of collecting duct

A

some but less than other areas

27
Q

passive resorption

A

urea and water

28
Q

active reabsorption

A 
glucose
AA
sodium
potassium 
calcium 
Vit C 
uric acid
29
Q

consequence of reabsorption relying on ATPase

A

susceptible to metabolic poisons

30
Q

why is secretion important in the PCT

A

excretion

drugs enter tubular fluid here and act further down

31
Q

explain how active sodium transport acts as the driving force for the reabsorption of water and other ions and molecules

A

Na/K pump keeps [Na} inside cell low = large conc and electrical gradients
Na enter cell down conc grad allow uphill entry of glucose adn aa and exit of H+ by secondary AT
glucose and AA then cross basolateral membrane passively

32
Q

effect of carbonic anhydrase on Na handling

A

proton pumped out - neutralisen bicarb in tubular fluid
H2O and CO2 diffuse into cell
carbonic anhydrase catalyses formation of bicarb
bicarb then leaves the cell down conc grad
this is dependant on the Na/H+ transporter

33
Q

Na handling in DCT

A

linked to Ca reabsorption
Na pumped out
Na can enter through Na/Cl cotransporter or Ca/Na transporter

34
Q

thiazide action in DCT

A

block Na/Cl
more Na enters and Ca leaves
therefore larger Ca conc grad so Ca enters via passive system and conc in cell increases

35
Q

macula densa

A

part of juxtaglomerular apparatus
detects change in [Na] of filtrate
controls renin-ang system

36
Q

collecting duct and distal DCT

A

fine tune filtrate
Na reabsorbed depending on aldosterone
adjustment of Na, K, H, NH4
water controlled - ADH

37
Q

principle cell

A

important in Na/K and H2O balance
mediated by Na/K ATP pump
apical Na channel mediated by aldosterone, linked K channel
very TJ - little paracellular transport

38
Q

intercalated cell

A

acid base balance - mediated by H-ATP pump

39
Q

normal plasma osmolarity

A

140mmol/l

40
Q

what is the major solute and why

A

Na
most prevalent
and important
changes to regulate fluid vol

41
Q

effect of Na on body weight

A

high salt = retain more water = increased weight - go into positive balance
have less salt- negative balance = lose weight

42
Q

effect of increasing dietary Na

A

increased osmolarity
increased ECF vol - hold onto more water
increase Bp and vol

43
Q

effect of decreasing dietary Na

A

decreased osmolarity
decreased ECF - urinate more
decrease Bp and vol

44
Q

proportions of Na and where

A

reabsorb 65% in PCT - used to absorb glucose and AA
25% in ascending tubule
8% DCT
up to 2% collecting tubule

45
Q

effect if GFR on Na reabsorption

A

high GFR = high Na reabsorption
low GFR = low Na reabsorption
same proportion just physically less

46
Q

how can you change the amount of Na you excrete

A

change pressure in glomerular capillaries
change GFR
if reduce GFR more bypasses the tubular system

47
Q

method to increase Na reabsorption

A

happens when low BP - want to increase water retention
increase sympathetic activity - reduce GFR
also allows PCT to reabsorb more Na
stimulate granular cells in juxtaglomerular apparatus - secrete renin - stimulate ANG2 (vasoconstrict, increase BP, increase Na uptake in PCT) - stim aldosterone - change na uptake in dct and ct
low tubular Na in JGA - ang 2 secretion

48
Q

method to decrease Na reabsorption

A

atrial natriuretic peptide
change diameter of afferent and efferent arterioles
suppress activity in OCT, JGA and CT

urinary system (9 decks)

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