session 1- introduction Flashcards
which kidney hangs lower and why
the right kidney hangs lower because of the large liver
what are the functions of the kidney
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
in a 70kg male what much water do they contain
How much is in ICF
and in ECF
42L
28L
14L
What is the composition of electrolytes in ICF
and ECF
ICF- high potassium, low sodium, many large organic anions
ECF- low potassium, high sodium main anions are chloride and hydrogen carbonate
how many liters of ECF does the kidney filter per day
and how many liters exits as urine per day
180L
1.5L
Where does filtration take place
at the glomerulus proximal convoluted tubule loop of henle distal convulted tubule collecting duct
in a healthy person who is normal and electrolyte balance, what percentage of water, sodium and chloride ions is recovered
99%
in a healthy person who is normal and electrolyte balance, what percentage of bicarbonate, amino acids and glucose is recovered
100%
what is filtered through the glomerulous
water, electrolytes and small molecules are forced through it by a constant filtration pressure in the capillaires
what is the major site of re-absorption
PCT
What are the cellular mechanisms behind reabsorption
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
what is reabsorbed at the loop of henle and what is its function
what is the fluid leaving the loop of henle like
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
what is reabsorbed at the DCT
what does it actively secrete
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)
how does the re-absorption in the collecting duct place
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
what is the action of the distal nephron and what systems is it controlled by
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
where do loop diuretics act and what channel do they affect
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
where do thiazides act and what channel do they affect
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
where does amiloride act and what channel does it affect
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
where does anti diuretic hromone act and what channel does it affect
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
where does aldoesterone act and what channel does it affect
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
where does spironolactone act and what channel does it affect
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
how is sodium and bicarbonate reabsorbed in the early proximal tubule
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
how is chloride reabsorbed throughput the proximal tubule
via the anion exchanger chloride enters the cell via the lumen
chloride leaves basolateral membrane via KCl co-transporter
describe the uptake of sodium and chloride in the late proximal tubule
they diffuse through tight junctions
describe phosphate reuptake in the proximal tubule
what hormones is it regulated by
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
describe glucose reuptake in the proximal tubule
glucose is cotransported with sodium across the apical membrane SGLT2
glucose transported across basolateral membrane via the GLUT2 transporter (passive)
describe amino acid reuptake in the proximal tubule
cotransported across apical membrane via sodium dependent amino acid transporters
min acid passively transported basolateral membrane
describe urea uptake in the proximal tubule
soidum and urea contransported across apical membrane
urea passively transported across basolateral membrae
describe albumin reuptake in the proximal tubule
uptake is via receptor mediated endocytosis across apical membrane
then amino acids are transported passively across the basolateral membrane
describe vitamin B12 reuptake in the proximal tubule
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
describe vitamin D3 reuptake in the proximal tubule
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
describe calcium reuptake in the proximal tubule
calcium flows into the cell via Calcium Magnesium channel TRPV6 channel
then transported across basolateral membrane via NCX
describe potassium reuptake and secretion in the thick ascending limb
transported across apical membrane via NKCC2 channel
transported acoss basolateral membrane via KClCT
describe organic acid secretion in the proximal tubule
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
