session 1- introduction

Question 1

which kidney hangs lower and why

Answer 1

the right kidney hangs lower because of the large liver

Question 2

what are the functions of the kidney

Answer 2

regulation- controls concentration of key substances in ECF
excretion- excretes waste prodcuts
endocrine- synthesis of renin, eryhtropoietin, prostaglandins
metabolism- active form of vitamin D, catabolism of insulin, PTH caclitonin

Question 3

in a 70kg male what much water do they contain
How much is in ICF
and in ECF

Answer 3

42L
28L
14L

Question 4

What is the composition of electrolytes in ICF

and ECF

Answer 4

ICF- high potassium, low sodium, many large organic anions

ECF- low potassium, high sodium main anions are chloride and hydrogen carbonate

Question 5

how many liters of ECF does the kidney filter per day

and how many liters exits as urine per day

Answer 5

180L

1.5L

Question 6

Where does filtration take place

Answer 6

at the glomerulus
proximal convoluted tubule
loop of henle
distal convulted tubule
collecting duct

Question 7

in a healthy person who is normal and electrolyte balance, what percentage of water, sodium and chloride ions is recovered

Answer 7

99%

Question 8

in a healthy person who is normal and electrolyte balance, what percentage of bicarbonate, amino acids and glucose is recovered

Answer 8

100%

Question 9

what is filtered through the glomerulous

Answer 9

water, electrolytes and small molecules are forced through it by a constant filtration pressure in the capillaires

Question 10

what is the major site of re-absorption

Answer 10

PCT

Question 11

What are the cellular mechanisms behind reabsorption

Answer 11

tubules are lined with epithelial cells which are polarised- this allows sodium potassium pump to move sodium from the tubular cell into the ECF and potassium from the ECF into the lumen
sodium enters across the luminal membrane down concentration gradient,
energy from sodium movement drives re-absorption of glucose
water folows electrolytes osmotically

Question 12

what is reabsorbed at the loop of henle and what is its function
what is the fluid leaving the loop of henle like

Answer 12

further salt re-absorption
major function is to create a gradient of increasing osmolarity in the medulla by counter current multiplication to allow the formation of concentrated urine if water has to be conserved
fluid leaving loop of henle is hypotonic

Question 13

what is reabsorbed at the DCT

what does it actively secrete

Answer 13

major site of variable re-absorption of electrolytes and water
as fluid leaving the loop of henle is hypotonic
distal tubule removes more sodium and chloride

actively secretes hydrogen ions
water may or may not follow re-absorption of electrolytes
if it does not then large volumes of dilute urine are formed (diuresis)

Question 14

how does the re-absorption in the collecting duct place

Answer 14

the collecting duct passes through the high osmolarity environment of the medulla (created by the loop of henle)
if water can cross the epithelium, it will leave the urine down the osmotic gradient- producing a low volume of concentrated urine
if it cannot the urine remains diluted

this is all controlled by the amount of ADH present

Question 15

what is the action of the distal nephron and what systems is it controlled by

Answer 15

sodium recovery - controlled by RAAS (controls ECF volume)
water recovery- controlled by ADH (controls permeability of DCT and collecting duct to water which controls ECF osmolarity

Question 16

where do loop diuretics act and what channel do they affect

Answer 16

loop diuretics act in the thick ascending limb
they work by blocking the NKCC2 channel
this reduces sodium uptake from the lumen into the cell and so reduces water uptake
so an increased volume of urine is formed

Question 17

where do thiazides act and what channel do they affect

Answer 17

thiazides act in the distal convoluted tubule
they work by blocking the NCCT
This reduces the entry of sodium and chloride into the cell from the lumen so less water follows
so an increased volume of urine is formed

Question 18

where does amiloride act and what channel does it affect

Answer 18

amiloride acts in the Distal convoluted tubule and cortical collecting duct
it works by blocking the eNaC
this reduces the entry of sodium into the cell from the lumen so less water follows
so an increased volume of urine is formed

Question 19

where does anti diuretic hromone act and what channel does it affect

Answer 19

ADH acts in the cortical collecting duct
it works by inserting aquaporin channels into the apical membrane
this means more water in the lumen enters the cell
so there is less water that is filtered out in the urine
so a decreased volume of urine is formed

Question 20

where does aldoesterone act and what channel does it affect

Answer 20

aldosterone acts in the cortical collecting duct
it works by increasing sodium rebasorbtion via the epithelial sodium channel
this means more sodium enters the cell
so more water follows
and less water is excreted in urine

Question 21

where does spironolactone act and what channel does it affect

Answer 21

spironolactone acts in the cortical collecting duct
it is an aldosterone antagonist
spironolactone blocks aldosterone working on eNaC
this means less sodium can enter the cell from the lumen
so less water follows
so more water is excreted in urine

Question 22

how is sodium and bicarbonate reabsorbed in the early proximal tubule

Answer 22

carbonic anhydrase causes hydrogen bicarbonate to become water and carbon dioxide in the lumen
this allows it to be transporters across the apical membrane
in the cell carbonic anhydrase recombines water and crabon dioxide to form bicarbonate
it dissociates into hydrogen carbonate and hydrogen
the hydrogen carbonate is transported into the capillary via the anion exchanger

Question 23

how is chloride reabsorbed throughput the proximal tubule

Answer 23

via the anion exchanger chloride enters the cell via the lumen
chloride leaves basolateral membrane via KCl co-transporter

Question 24

describe the uptake of sodium and chloride in the late proximal tubule

Answer 24

they diffuse through tight junctions

Question 25

describe phosphate reuptake in the proximal tubule

what hormones is it regulated by

Answer 25

phosphate is transported across the apical membrane via a sodium dependent phosphate transporter
then it is passively transported across via passive phosphate transporters across the basolateral membrane and into the capillary
regulated by pararthyroid hormone and vitamin D

Question 26

describe glucose reuptake in the proximal tubule

Answer 26

glucose is cotransported with sodium across the apical membrane SGLT2
glucose transported across basolateral membrane via the GLUT2 transporter (passive)

Question 27

describe amino acid reuptake in the proximal tubule

Answer 27

cotransported across apical membrane via sodium dependent amino acid transporters
min acid passively transported basolateral membrane

Question 28

describe urea uptake in the proximal tubule

Answer 28

soidum and urea contransported across apical membrane

urea passively transported across basolateral membrae

Question 29

describe albumin reuptake in the proximal tubule

Answer 29

uptake is via receptor mediated endocytosis across apical membrane
then amino acids are transported passively across the basolateral membrane

Question 30

describe vitamin B12 reuptake in the proximal tubule

Answer 30

receptor mediated endocytosis
vitamin b12 binds to transcobalmain in the kumen
b12 bound to transcobalmain binds to megalin receptor
enodcytosis of this unit into tubular cell
vitamin b12 dissociates

Question 31

describe vitamin D3 reuptake in the proximal tubule

Answer 31

receptor mediated endocytosis
25-(OH) Vitamin D3 binds to a vitamin D binding protein
this binds to the megalin receptor which udergoes endocytosis across the apical membrane
the inactiveform of vitamin D is converted to 1,25-(OH) the active form of vitamin D in the tubular cell

Question 32

describe calcium reuptake in the proximal tubule

Answer 32

calcium flows into the cell via Calcium Magnesium channel TRPV6 channel
then transported across basolateral membrane via NCX

Question 33

describe potassium reuptake and secretion in the thick ascending limb

Answer 33

transported across apical membrane via NKCC2 channel

transported acoss basolateral membrane via KClCT

Question 34

describe organic acid secretion in the proximal tubule

Answer 34

chloride, hydrogen carbonate, and hydorxyl are transported across the apical membrane via the acid base excahnger
acid is trasported across the basolateral membrane via the acid antiporter