MS

• what is osmolality?


  concentration of molecules per weight of water
• when are diuretics needed?

  to reduce fluid overload in circulation by getting rid of more fluid in the urine
• how do diuretics promote fluid excretion?

  preventing salt reabsoprtion
• what is osmotic diuresis?

  - when there is an excess of plasma glucose, it will not all be reabsorbed

  - the remaining glucose in the urine draws water in by osmosis

  - therefore more fluid is excreted in the urine
• what substance is used to clinical 'mimic' osmotic diuresis?

  mannitol
• where would mannitol work?

  pct
• where do carbonic anhydrase inhibitors act?

  pct
• what transporter usually allows reabsorption of Na+ in the pct?

  Na+/H+ antiporters
• what happens to H+ ions after Na+/H+


  reacts with HCO3- and generates CO2 then reconverted back to H+ and HCO3- by carbonic anhydrase
• what effect do carbonic anhydrase inhibitors have on excretion?

  inhibits the reconversion back to H+ and HCO3- so less Na+ is secreted via Na+/H+ antiporters and more remains in the tubular fluid, meaning more fluid also remains in tubular fluid
• where do loop diuretics work?

  thick ascending loop of henle
• what do loop diuretics do?

  inhibit Na+/2Cl-/K+ transporters
• what is the effect of inhibiting Na+/2Cl-/K+ transporters?

  less Na+ reabsorbed and more remains in tubular lumen, hence more fluid also remains in tubular lumen
• where is the main centre for renal control of fluid balance?

  osmoreceptive complex
• what two nuclei receive input from the osmoreceptive complex?


  - supraoptic (SO)

  - paraventricular (PVN)
• where are the supraoptic and paraventricular nuclei located?

  hypothalamus
• what do the supraoptic and paraventricular nuclei do?

  synthesise 2 peptide hormones
• what 2 peptide hormones do the supraoptic and paraventricular nuclei synthesise?

  - vasopressin/ADH

  - oxytocin
• what receptors can vasopressin bind to?

  - V1a

  - V1b

  - V2
• where are V1a and V2 receptors found?

  in peripheries
• where are V1b receptors?

  central nervous system
• where exactly are V2 receptors located?

  basolateral membrane of principal cells in collecting ducts
• where does vasopressin bind when entering the kidneys?

  V2 receptors on principal cells
• what happens when vasopressin binds to V2 receptors?

  causes increase in number of AQP2 channels in apical membrane
• what channels are already located on basolateral membrane of principal cells?

  AQP3 and AQP4
• what are the three most water permeable areas of the nephron?

  - proximal convoluted tubule

  - descending limb

  - inner medullary collecting duct
• how much water is reabsorbed in the pct?

  65%
• how much water is reabsorbed in the descending thin limb?

  15%
• how much water is reabsorbed in the collecting duct?


  remainder - depending on vasopressin
• what are the 3 places of most passive NaCl permeability?

  - pct

  - descending limb

  - ascending thin limb
• where is the main place for active NaCl transport?

  thick ascending limb
• where does the the nephron become impermeable to urea?

  from thick ascending limb to inner medullary collecting duct
• what is happens to the osmolarity from the cortex to tip of medulla?

  increases
• what is the counter-current hypothesis?

  loop of henle creates a system where fluid is flowing in different directions but with different permeabilities and transport properties
• what is the permeability to water in the thin descending limb?

  high permeability
• what is the permeability to water in the thin ascending limb?

  lower permeability
• what is the permeability to water in the thick ascending limb?

  very low permeability
• do many substances get transported out the descending limb?

  no
• what substances get transported out of the thick ascending limb?


  Na+, K+ and Cl-
• what happens to the Na+ Cl- transported out of the thick ascending limb?

  get absorbed into descending limb