tubular function

Question 1

processes that remove and return substances to the blood

Answer 1

filtration
reabsorption
secretion

Question 2

why do you need reabsorption

Answer 2

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

Question 3

transcellular

Answer 3

substances move through the cell

Question 4

paracellular

Answer 4

substances travel through the TJ between the cells

Question 5

are secretion and reabsorption trans/paracellular

Answer 5

both can occur through both pathways

Question 6

transport of lipophilic molecules

Answer 6

lipid soluble
rate only dependant on concentration - linear
protein independent

Question 7

transport of hydrophilic molecules

Answer 7

gated through proteins

rate limited by protein transporters

Question 8

Kinetics for active movement

Answer 8

same as for facilitative transport

Question 9

direct AT

Answer 9

directly coupled to ATP hydrolysis

Question 10

secondary AT

Answer 10

indirectly coupled to ATP hydrolysis

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

Question 11

water transport

Answer 11

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

Question 12

protein reabsorption

Answer 12

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

Question 13

transport maxima

Answer 13

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

Question 14

describe secretion

Answer 14

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

Question 15

substances that are secreted

Answer 15

most important - H+ and K+

choline, creatinine, penicillin and other drugs

Question 16

renal tubular acidosis

Answer 16

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

Question 17

bartter syndrome

Answer 17

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%

Question 18

Fanoci syndrome

Answer 18

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

Question 19

percentage of water reaching different points in nephron

Answer 19

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

Question 20

where are most of the Na transporters

Answer 20

PCT

Question 21

amount of solute reabsorbed in the PCT

Answer 21

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

Question 22

structure of PCT

Answer 22

dense brush border = large SA

a lot of mt

Question 23

structure of descending loop of henle

Answer 23

few mt

loose TJ

Question 24

structure of ascending limb

Answer 24

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

Question 25

structure of DCT

Answer 25

a lot of mt | squamous epi

Question 26

structure of collecting duct

Answer 26

some but less than other areas

Question 27

passive resorption

Answer 27

urea and water

Question 28

active reabsorption

Answer 28

``` glucose AA sodium potassium calcium Vit C uric acid ```

Question 29

consequence of reabsorption relying on ATPase

Answer 29

susceptible to metabolic poisons

Question 30

why is secretion important in the PCT

Answer 30

excretion | drugs enter tubular fluid here and act further down

Question 31

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

Answer 31

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

Question 32

effect of carbonic anhydrase on Na handling

Answer 32

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

Question 33

Na handling in DCT

Answer 33

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

Question 34

thiazide action in DCT

Answer 34

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

Question 35

macula densa

Answer 35

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

Question 36

collecting duct and distal DCT

Answer 36

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

Question 37

principle cell

Answer 37

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

Question 38

intercalated cell

Answer 38

acid base balance - mediated by H-ATP pump

Question 39

normal plasma osmolarity

Answer 39

140mmol/l

Question 40

what is the major solute and why

Answer 40

Na most prevalent and important changes to regulate fluid vol

Question 41

effect of Na on body weight

Answer 41

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

Question 42

effect of increasing dietary Na

Answer 42

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

Question 43

effect of decreasing dietary Na

Answer 43

decreased osmolarity decreased ECF - urinate more decrease Bp and vol

Question 44

proportions of Na and where

Answer 44

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

Question 45

effect if GFR on Na reabsorption

Answer 45

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

Question 46

how can you change the amount of Na you excrete

Answer 46

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

Question 47

method to increase Na reabsorption

Answer 47

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

Question 48

method to decrease Na reabsorption

Answer 48

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