Lecture 33: Tubular Reabsorption and Secretion Flashcards
Objectives – Describe the functional and histological differences of cells in different regions of the nephron – Explain the concept of renal threshold – Describe how the osmolarity of the filtrate changes during passage through the loop of Henle – Describe the differences in osmolarity within the extracellular spaces of the kidney medulla – Explain the significance of countercurrent multiplication
nephron reabs rate
99% filtrate
proximal convouted tubule does most reabs
rest of nephron does fine tuning
nephron filtrate fine tuning
solutes reabs by active and passive processes
water follows solutes (osmosis)
small proteins move across blood by pinocytosis.
tubular secretion
transfers materials from blood to tubular fliud
helps control blood pH b/c H secretion
helps eleimaten substances (NH4, creatine, K)
Paracellular reabsorbtion
50% reabs matreial moves beteween cells by diffusion in some parts of tubule
cross ONE membrane
Transcellular reabs
material moves through both basal and apical membranes of tubule by ACTIVE TRANSPORT
reabs of Na+
important!!!
several transport system exist for it
Na/K ATPase pumps sodium from tubule cell cytosal th BASOLATERAL membrane only
water reabsoprtion
Osmosis ONLY
obligatory water reabsorption
water “obliged” follow solutes being reabsorbed
moving ions from chamber A to B
facultative water reabsorption
in collecting duct under control of ADH
Reabs in PCT: Na symporters
help reabs materials from tubular filtrate
glucose, Amino acids, lactic acid, water sol vitamins
intracellular sodium levels kept low due to Na+/K+ pump on basolateral side
PCT functions
reabs of nutrrients isosmotic reabsorption (at same osmotic level of blood)
Glucosuria
when renal symporters cant reabs glucose fast enough
happens when blood glucose above 200 mg/mL–> some glucose stays in urine
caused often by diabetes mellitus b/c insulin activity defcient and blood glucose too high
osmolytes
characteristic renal threshold valules
renal clerance rates
inulin, creatinine)
symporters in loop of Henle
thick asceding has Na, K-, Cl- symportes that reabs ions. Immpermeable to water!!!!
K+ moves back into filtrate through K+ leach channles
Na pumped out on basolateral side
Cl- diffuses across cell
symporters in loop of Henle: why cations do what they do
cations passively move to vasa recta
drawn to neg charge in capp
Formation of Dilute Urine
drinking water-> dec blood osmolarity-> ADH inhibited
goal: removed excess fluid from blood by making dilute urine
formation of dilute urine in depth
blood plasma: 300 mOsm/L conc (normal for blood)
this is when we have low blood osmolarity
filterate osmolaraity INCREASES as it moves down desc. loop of henle
filtrate osmolarity decs as it moves up as loop of henlee
dec in collecting duct (impermeable to water) -> dilute urine
Formation of concentrated urine
water deprivation-> inc blood osmolarity-> ADH stim
goal: prevent water loss and make concentrated urine
formation of concentrated urine in depth
JG LHs (long ones)
in LH: similar to making dilute BUT: we are losing a lot of water so we need to get rid of solutes so we can get back to being isosmotic with blood. So we do the extra suff
in the CD: reabs more water when we have ADH (makes aquporins) (also principle cells reabs mor water when ADH present
ALSO:::: Urea RECYCLING: builds up in RENAL MEDULLA (not in tubule fluid)
ADH actions
stim Na, K, CL symporters in thick ascending loop of henlee: builds osmotic gradient in intersitial fluid
stim water reabs in upper collecting ducts
stim water reabs and urea recycling in lower collecting ducts builds osmotic gradient in ISF
result: concentrated urine
countercurrent mechanism descending loop
descending loop of henle is very permeable to water
high osmolarity of ISF outisde descending loop= water move out of tubule by osmosis,
at hairpin turn ,osmolarity of filtrate can reach 1200 mOs,/L
countercurrent mechanism ascending loop
ascending loop impermeable to water, so ions move OUT
BUT: symporters reomve Na, Cl so osmolarity of filtrate drops to 100 mOsm/L, but less filtrate left in tubule
slide 4
slide 4
which part of LH is impermeable to water?
thick ascending limb
apical membrane permeability
impermeable to water
chloride
diffuses into basolateral side fluid
potassium
goes into fluid on apical side
ISF charge
more negative than fluid in lumen
in depth concentrated urine part 2
urea recycling=urea build up in renal medulla. it passes through CD into ALH and DLH
b/c three things running in parallel loops
1. loop of henlee
2. peritubular capillaries
3. vasa recta
then put it in medulla, which has lots of urea
