Physiology 4 & 5

Question 1

where does most of tubular reabsorption occur

Answer 1

the proximal tubule of the nephron

Question 2

why is tubular reabsorption necessary

Answer 2

because the kidneys filter 180 litres per day so without it we would pee out our plasma volume 65 times a day

Question 3

what do the kidneys reabsorbed (important ones) (and percentages)

Answer 3

99% of fluid 
99% of salt 
100% of glucose 
50% of urea 
0% of creatinine

Question 4

why is reabsorption specific for different molecules

Answer 4

because it relies on specific transporter proteins for specific molecules

Question 5

how much filtered fluid is reabsorbed in the proximal tubule

Answer 5

80ml/min

Question 6

what substances are reabsorbed in the proximal tubule

Answer 6

sugar 
amino acids 
phosphate 
sulphate 
lactate

Question 7

what substances are secreted into the proximal tubule

Answer 7

H+ ions 
Hippurates 
Neurotransmitters
Bile pigments 
Uric acid 
Drugs (atropine, morphine, penicillin) 
toxins

Question 8

what is transcellular reabsorption

Answer 8

reabsorption which involves the molecule traveling through the epithelial cells of the tubule and out the other side into the interstitial fluid and then into the capillary

Question 9

at what points does transcellular reabsorption need transporter proteins

Answer 9

between lumen of the tubule and the epithelial cell membrane

between the epithelial cell membrane and the interstitial fluid

Question 10

what is paracellular reabsorption

Answer 10

when the molecule being absorbed travels through the gaps in between the epithelial cells

(depends on how tightly they cells are pushed together, some segments of the tubule are tighter than others)

Question 11

what are the 3 types of carrier mediated membrane transport

Answer 11

primary active transport
secondary active transport
facilitated diffusion

Question 12

what is primary active transport

Answer 12

when a transporter protein uses ATP to transport a molecule against its concentration gradient (Na/K pump)

Question 13

what is secondary active transport

Answer 13

couples the movement of an ion (Na) down its concentration gradient with another ion needing moved

can be symport - same direction or antiport - opposite direction

Question 14

what is facilitated diffusion

Answer 14

movement of a substrate down its existing concentration gradient

uses a transport protein instead of relying on diffusion across the membrane

Question 15

what transport allows salt reabsorption in the proximal tubule

Answer 15

primary active transport with a Na/K pump

Question 16

how is salt moved from the tubule into the blood

Answer 16

Na/k pump keeps the Na level inside the cell less than out in the insterstitial fluid

this concentration gradient is used to drive sodium out the capillary and into the cell

Na/k pump pumps it out of the cell into the interstitial fluid

this sets up an electrical gradient allowing Cl- ions and water to pass in paracellularly

oncotic drag then pulls the salt and water into the capillary

Question 17

what route of reabsorption does water take out of the tubule and into the interstitial fluid

Answer 17

transcellular route following the concentration gradient set up by Na in the interstitial fluid

Question 18

what is oncotic drag

Answer 18

when the capillary is full of plasma proteins because it has lost all of its plasma to filtration it has a v high osmolarity

this causes it to pull salt and water out of the interstitial fluid in

Question 19

what transporter moves glucose in reabsorption

Answer 19

Glucose Na transporter - symporter (couples movement of glucose to sodium as it comes into the cell)

water then follows this paracellularly

water and glucose then pulled into the capillary via oncotic drag

Question 20

why is there glucose in the urine of diabetics

Answer 20

because when blood glucose is v high the the transport membranes become saturated and cannot reabsorb all the glucose coming through

it then passes through the tubules and is excreted in the urine

Question 21

what does para-aminohippurate acid (PAH) measure

Answer 21

renal plasma flow

Question 22

what is the cortico-medullary concentration gradient

Answer 22

a gradient that exists within the interstitial fluid - becoming more concentrated as you follow the loop of Henle down into the medulla

Question 23

what is the purpose of the cortico-medullary concentration gradient

Answer 23

to allow concentrated urine to be produced

Question 24

what allows juxtamedullary nephrons to produce more concentrated urine

Answer 24

their loop of Henle is longer so they are more exposed to the aortic-medullary concentration gradient

Question 25

what is reabsorbed in the descending limb of the loop of Henle

Answer 25

water NOT SALT

Question 26

what is reabsorbed in the ascending limb of the look of Henle

Answer 26

SALT not water

Question 27

what does the triple co-transporter on the luminal membrane of the ascending tubule do

Answer 27

moves Na, K and Cl ions from the tubular fluid into the epithelial cell

Question 28

what stops water from being absorbed in the ascending tubule

Answer 28

the epithelial cell junctions are too tight so it can't cross paracellularly

Question 29

what happens to potassium ions than come into the epithelial cell via the triple co-transporter

Answer 29

some are recycles and put back into lumen excess k and Cl move into interstitial fluid via K Cl transporter

Question 30

what do loop diuretics do

Answer 30

stop the activity of the triple co-transporter so stop salt reabsorption in the kidneys (so you have less salt and K in the blood)

Question 31

what causes water to leave the descending limb

Answer 31

the high osmolarity of the interstitial fluid caused by the NaCl from the ascending limb being pumped in?

Question 32

what happens to the interstitial fluid the further down the loop of Henle you go

Answer 32

it gets more concentrated

Question 33

What is the ideal concentration gradient between the ascending limb and the interstitial fluid

Answer 33

200 mili osmols

Question 34

how does the ascending limb achieve this gradient

Answer 34

by pumping out sodium into the interstitial fluid (as soon as new filtrate comes in)

Question 35

what does the descending limb do in response to the increases osmolarity of the interstitial fluid (due to the increase in salt put there by the ascending limb)

Answer 35

matches it by loosing water via osmosis

Question 36

in the steady state what is the highest concentration achieved by the cortico-medullary concentration gradient

Answer 36

1200 mili osmols

Question 37

What is the ideal concentration gradient between the ascending limb and the interstitial fluid

Answer 37

200 mili osmols

Question 38

how does the ascending limb achieve this gradient

Answer 38

by pumping out sodium into the interstitial fluid (as soon as new filtrate comes in)

Question 39

what does the descending limb do in response to the increases osmolarity of the interstitial fluid (due to the increase in salt put there by the ascending limb)

Answer 39

matches it by loosing water via osmosis

Question 40

in the steady state what is the highest concentration achieved by the cortico-medullary concentration gradient

Answer 40

1200 mili osmols