Tubular Transport of NaCl and H2O Flashcards
For water and NaCl
a) amount filtered of each
b) percent of filtered amount that is reabsorbed
overall, how significant is regulation for reabsorption
Water
a) 190L
b) > 86% reabsorbed
NaCl
a) 1500 g
b) > 98% reabsorbed
most filtered water + salt is reabsorbed so small fraction under homeostatic control –> regulation only affects 14% water, < 2% NaCl not auto reabsorbed
Movement of
1) Na+
2) Cl-
3) H2O (2 routes)
1) Na+ flows down gradient passively then pumped out other side (serosal)
2) Cl- travel through tight junction following Na+ (paracellular)
3) Osmotic pressure of Na+, Cl-, causes water to follow via either aquaporis on apical/basolateral or through tight junctions in proximal tubule (paracellular or transcellular)
Movement of glucose and other active metabolites
Filtered
Cotransporter using energy from Na+ downhill gradient coupled to flow of glucose against gradient (2ndary active transport)
Glucose then passively diffued across
All energy fro ion and H2O movement is derived from ___
Na+/K+ ATPase
Epithelial transport mechanism of Prox Tubule
1) What gets transported and how?
2) max ____ rate for each substance because?
3) tubular fluid is ___
1) Na+ transferred from lumen of epith cell to serosa (basolateral) via Na+/K+ ATPase
2) Na+ passive from lumen into cell
3) Cl- follow Na+ via tight junction
4) water follows due to osmosis from Na+ and Cl-
5) also glucose + other metab (AA and HCO3-) using Na+ gradient
_____
2) reabsorption rate because discrete # of transporter
____
ISOTONIC FLUID
EPITHELIAL TRANSPORT MECHANISM FOR LOOP OF HENLE!
1) what gets transferred and how
2) tubular fluid becomes ___ and interstitium becomes ___
1) NaCl reabsorption in ascending loop via Na+/K+/2cl- cotransporter on lumen side and Na+/K+ ATPase on serosal side
ASCENDING = IMPERMEABLE TO H2O
2) NaCl reabsorbed in descending loop and water reabsorbed due to osmosis and incr permeability but GREATER NACL REABSORB COMPARED TO WATER
____
TUBULAR FLUID = hypotonic
interstitium = hypertonic (more NaCl reabsorbed)
Mechanism of epithelial transport in distal tubule and collecting ducts
1) what is transported and how
2) how is this segment different from other loop of henle and proximal tubule
same exactly as prox tubule ==> Na+, Cl-, and Water reabsorbed
____
2) differs because reabsorption is varied by circulating hormones and there are tight junctions between individual cells so most reabsorption occurs TRANSCELLULARLY
Aldosterone and ADH incr NaCl and H2O reabsorption
What is a common target of loop diuretics
Na+/K+/2Cl- channel in loop of henle
Effect of aldosterone in fine tuning distal tubule/collecting duct
Creates more Na+ pumps and channels in DT/CD –> incr Na+ reabsorption
incr ATP synthesis for the pumps
Mechanism of how aldosterone incr Na+ pumps
1) Aldosterone enters cell and hits receptor
2) aldosterone + receptor –> nucleus to turn on genes and make more Na+ pumps on BASOLATERAL surface and channels on APICAL surface–> INCR NA+ REABSORBED
also vesicles already making pumps/channels that can be integrated more quickly than making new channels/pumps
HOURS!!!!
Mechanism of ADH/vasopressin on channels in cell
1) ADH + ADH receptor cause pre-formed vesicles with aquaporins to enter into apical (lumenal) membrane TO INCR REABSORPTION OF H2O
2) interstitium is hypertonic because 25% of Na+ reabsorption in ascending limb (IMPERMEABLE TO WATER) drives water gradient
RAPID AND SHORT
Amount of H2O reabsorpton in
1) proximal tubule
2) descending lop
3) ascending lop
4) fine tuning (obligatory vs. hormones)
1) 65%
2) 15%
3) 0%
4) 6% obligator
14% hormones
Amount of NaCl reabsorpton in
1) proximal tubule
2) descending lop
3) ascending lop
4) fine tuning (obligatory vs. hormones)
1) 65%
2) 0%
3) 25%
4) 8% obligatory
2% hormones
Unique permeability traits of
1) proximal tubule
2) descending loop
3) ascending loop
1) isotonic, also glucose, AA, bicarb reabsorbed
2) impermeable to NaCl
3) impermeable to H2O
proximal tubule and loop of henle are responsible for the ___, ____ reabsorption of salt and H2O
distal tubule and collecting duct responsible for the ____ in maintaining homeostaiss and a degree of ___
obligatory, unregulated
regulatory control of reabsorption; fine tuning
where do adh/vasopressin and aldosterone act?
distal tubule/collecting duct
STARLING EQUATION FOR flow of sodium from renal interstitium to peritubular capillaries
when does it apply?
what is the main driving force for flow?
after H2O and salt reabsorbed from nephron –> must reach capillaries
Fic = K’ (Pint + πcap – Pcap – πint)
colloid oncotic pressure (πcap) due to extraction of H2O from plasma upstream from capillary through glomerular filtration
Define variables in Starling equation and give values for each
Fic= flow from interstitium to capillary = ΔP/R, 1/R = K’
Pint= pressure in interstitium from all the H2Oin that space=7mmHg
Pcap= pressure in the capillary resisting the pressure in the interstitium = 11 mmHg
πcap= osmotic capillary pressure drawing fluid into the capillary = 35 mmHg
πint= osmotic pressure in interstitium keeping fluid in the interstitium = 6 mmHg
Net filtration pressure (NFP) for reabsorbtion = 25 mmHg
Starling force is entirely ___ generated flow because of albumin in blood leftover
osmotically
capillary very permeable to Na+
What is the effect of incr and decr tubular flow on water and sodium excretion and reabsorption
1) incr tubular flow, decr reabsorption, incr excretion of substances (ex = diuretics)
flow too fast in tubule so less chance to interact with transporters for reabsorption
so more substance escape reabsorption
2)decr tubular flow, incr reabsorption, decr excretion of substances
what is purpose of glomerulotubular balance and tubuloglomerular feedback
maintaining constant delivery of water and NaCl to distal tubule and collecting duct despite changes in GFR
Define glomerulotubular balance
ability of obligatory reabsorption in proximal tubule to compensate for changes in filtered load
ex:proximal tubule reabsorption readjusts to filtration changes so FIXED PROPORTION OF FILTERED WATER AND NaCl ALWAYS REABSORBED = 65%
xDefine tubuloglomerular feedback
regulates GFR in each nephron in response to changes in NaCl concentration by special epithelial cells = macula densa
contact afferent arteriole–> cause arteriole to constrict or dilate
Describe macula densa cells
in contact with afferent arteriole –> cause constrict or dilate
start of distal tubule –> monitor status of obligatory reabsorption just before fluid enters fine tuning segments
what is the effect of incr GFR on tubular fluid flow
mechanism of tubuloglomerular feedback
1) initial incr GFR, incr in tubular fluid flow in ascending limb
2) decr % NaCl reabsorption in loop –> compensation by glomerulotubular balance in prox tubule (incr [NaCl] in lumen)
uncompensated part causes fluid to move faster in loop of henle
3) decr [NaCl] reabsorbed in ascending limb so NaCl incr in lumen of ascending and transported to macula densa
4) when fluid leaves loop, contacts macula densa –> senses incr in NaCl –> incr signaling to JGA –> causes afferent arteriole to contract
5) incr secretion of AGII and adenosine to constrict afferent arteriole
6) decr Pgc to return GFR back to normal
Causes of water intoxication
impaired GFR
using ecstasy
(ingest large volume of water overwhelming excretory abiility)
primary energetic event
Na+ pump out across basolateral via Na/K ATPase
Why is there a transport maximum for a given substance
glucosuria is a diagnostic indicator of ___
because fixed number of transporters in prox tubule
diabetes mellitus
Unique features of distal tubule
1) tight junctions = TIGHT so majority reabs through transcellular with selective transporter
2) rate of transport varied by circulating hormones
Action of ADH
1) phosphorylation cascade to initate synthesis of aquaporins
2) release of premade aquaporins from small vesicles into apical membrane
main driving force for reabsorption fo fluid is
why?
osmotic pressure of capillary plasma = 35 = colloid osmotic pressure of plasma
plasma has significant amount of water extracted upstream due to glomerular filtration
Effect of diuretics on tubular flow and excreteion
Diuretics incr urine output by decr water reabsorption
incr tubular flow rate past transporters
incr excretion rate of Na, K, Cl indirectly
What happens if imperfect autoregulation resulted in small 1 mm incr in Pgc at glomerulus
incr NFP from 6 –> 7
incr GFR by 17%
incr delivery of tubular fluid to fine tuning segments and majority escape reabsorption to be excreted
what happens if decr GFR and constant reabsorption
Pgc decr by 1 mm
complete obligatory reabsorption of filtered load
no excretion
