5 - reabsorption & secretion

Question 1

what is the result of 20% plasma being in the bowman’s capsule for filtration?

Answer 1

blood in the efferent arteriole and peritubular capillaries has higher plasma proteins conc and increased oncotic pressure

Question 2

what is the balance of starlings forces in these vessels and what does this mean?

Answer 2

decreased PC pressure and increased oncotic P

leads to reabsorption being favoured in PCs

Question 3

where is H2O, GLC etc. filtered and where is it then reabsorbed?

Answer 3

filtered in the glomerulus, reabsorbed in the proximal convoluting tubule

Question 4

name 3 substances that are reabsorbed by carrier mediated transport systems?

Answer 4

GLC
amino acids
phosphate

Question 5

why do carriers have a Tm?

Answer 5

saturation of carriers

Question 6

what is Tm?

Answer 6

maximum transport capacity

Question 7

result of Tm being exceeded?

Answer 7

excess substrate enters urine

Question 8

function of carrier molecules?

Answer 8

allow larger molecules (e.g. GLC) to cross the membrane for reabsorption

Question 9

how is Tm decided?

Answer 9

by the number of carriers

Question 10

what is the renal threshold?

Answer 10

plasma threshold @ which saturation occurs

Question 11

relationship between GLC plasma conc and how much is filtered?

Answer 11

whatever the GLC plasma conc, that amount will be filtered out

Question 12

what is the renal threshold for GLC?

Answer 12

10mmol/L

Question 13

Tm for GLC?

Answer 13

10mmol/L

Question 14

once it has all been filtered, what happens to GLC?

Answer 14

vast majority will be absorbed, if it exceeds 10mmol/L - some will be excreted

Question 15

normal plamsa GLC?

Answer 15

5 mmol/L

Question 16

how is GLC regulated?

Answer 16

insulin and counter regulatory hormones

Question 17

what is the benefit of Tm for GLC being set at 10 when the normals plasma GLC is only 5?

Answer 17

ensures that GLC is all reabsorbed as it is a precious energy source

Question 18

what is glycosuria?

Answer 18

GLC in urine

Question 19

what is glycosuria a result of?

Answer 19

failed insulin control, not failed kidneys

Question 20

why are sulphate and phosphate ions not regulated by Tm?

Answer 20

Tm is set at a level whereby normal blood plasma conc causes saturation of carriers

Question 21

what is the result of any increase in phosphate or sulphate molecules?

Answer 21

excretion

Question 22

effect of PTH on reabsorption of GLC?

Answer 22

decreased reabsorption

Question 23

describe 3 renal processes?

Answer 23

1 - substances reabsorbed by ,mediated transport systems

2 - reabsorption of Na+ ions

3 - tubular secretion

Question 24

where is Na+ most abundant?

Answer 24

ECF

Question 25

where is ~75% of Na+ reabsorption?

Answer 25

proximal tubule

Question 26

how is Na+ regulated?

Answer 26

by active transport, creating a gradient for Na+ to cross the tubule wall

Question 27

what drives the reabsorption of Na+?

Answer 27

Na+ pumps

Question 28

location of the Na+pumps?

Answer 28

on basolateral surfaces - i.e. high density of mitochondria

Question 29

how does Na+ move into cells?

Answer 29

passively

Question 30

why do Na+ ions move into cells passively?

Answer 30

due to brush border of proximal tubule cells having increased permeability to Na+ ions than other membranes

Question 31

why do proximal tubule cells have increased permeability to Na+ions?

Answer 31

due to microvilli (increased surface area) and increased number of Na+ ion channels