Loop of Henle - IN Flashcards
what are the general functions of the thin descending limb
low solute/high water permeability; osmotic equilibrium of the tubular fluid with the increasingly hypertonic interstitium results in water reabsorption with little solute reabsorption.
what are the general functions of the thin ascending limb
inner medulla) relatively impermeable to water; passive NaCl reabsorption driven by the high tubular fluid [NaCl]created in the thin descending limb; passive urea secretion
what are the general functions of the thick ascending limb
(outer medulla) relatively impermeable to water, but actively reabsorbs NaCl and K (via luminal Na/K/2Cl symporters). This effectively dilutes (decreases osmolarity below 100 mOsm/L – less than plasma) the tubular fluid. (*This is a unique instance where water does NOT follow solute).
what is the solute transport engine
the active reabsorption of Na and Cl that both drives and maintains a counter current multiplication of solute concentration differences
how do loop diuretics work, like furosemide
by inhibiting the Na/K/2Cl symporters which decreases reabsorption of NA, K and Cl while simultaneously increasing their excretion in the urine. Can theoretically cause excretion of as much as 25% of the filtered Na+.
whats the deal with ADH?
secreted by the posterior pituitary in response to increased plasma osmolarity. ADH increases the water permeability of the collecting duct, permitting water reabsorption back into the circulation and excretion of concentrated urine. More water is returned to the circulation when the plasma volume is contracted and/or hyperosmotic.
what happens to the collecting duct in the ABSENCE of ADH
it is impermeable to water, permiting the excretion of dilute urine
what is the controlling variable in determining excretion of dilute/concentrated urine
ADH - as collecting duct travels down to inner kidney, ADH controls how much water is reabsorbed - note - thin and thick ascending limbs and distal convoluted tubule are all insensitive to ADH
what does urea recycling in the inner medulla contribute to
solute concentration gradient in interstitium - in inner medullary collecting ducts, ADH increases water permeability and it increases transporter function for facilitated diffusion of urea, UT1
what are the vasa recta
‘peritubular’ capillaries that serve the medulla and papilla of the kidney, they follow the same course as the loop of Henle. The vasa recta participate in countercurrent exchange
what is countercurrent multiplication
establishes the corticopapillary osmotic gradient
what is countercurrent exchange
a purely passive process that helps maintain the gradient, helping to prevent “washout” of solute from the medulla. This is achieved by a slower rate of blood flow through the vasa recta.
what is diuresis
increased excretion of urine
what happens to tubular fluid osmolarity in diuresis
volume expanded, hyposmotic -decreased plasma osmolarity; osmolarity gradient from cortex to inner medulla in the medullary interstitium is less steep.
what effect does decreased ADH have on the inner medullary collecting duct
decrease both water and urea permeability causing a reduced reabsorption of water and urea -> increased secretion in urine
