Loop of Henle, Distal tubule & Collecting duct


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  • Created by: Becca
  • Created on: 27-12-13 14:19
What movement happens in the descending thin limb?
Highly permeable to water (AQP1), much less permeable to NaCl & urea, movement largely passive
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What movement happens in the ascending limb?
Impermeable to water, ~20-30% of Na+, Cl- & K+ reabsorbed. Little reabsoprtion happens in the thin ascending limb (passive), most reabsorption happens in the thick ascending limb
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What ion movement happens in the thick ascending limb?
1Na/2Cl/1K enter via apical membrane symporter, Cl leaves by passive diffusion (basolateral Cl- channels). Most K+ leaks back out (apical K+ channels), lumen becomes +ve charged, drives paracellular diffusion of Na/K/Ca/Mg
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How else do sodium ions enter cells in the thick ascending limb?
Na+ also enters cell via Na/H antiporter -> HCO3- reabsorption. Na entering ells pumped out across basolateral membrane by sodium pump, low [Na+] provides electrochemical gradient which drives movement of Na from tubular fluid into cell
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In thick limb, active transport of NaCl is not accompanied by water. What does this result in?
Ascending limb impermeable to water: reduces osmolality of tubular fluid (becomes hypo-osmotic, thick limb is "diluting segment") & makes interstitial fluid of medulla hyperosmotic (causes osmotic removal of H2O from descending limb/collecting duct)
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What happens in the early distal tubule?
Active dilution (impermeable to H2O + reabsorbs salt, osmolality falls below plasma), Na pump basolateral membrane, Na/Cl enter cell (symporter), Cl leaves (diffusion), Ca/Mg reabsorption, remaining filtered K reabsorbed, H secreted (act as buffers)
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What are the two cells in the late distal tubule/collecting duct? What is their role?
Principal cells: reabsorb Na+ & water, secrete K+, depends on activity of Na+ pump. Intercalated cells: secrete H+, reabsorb HCO3- & K+
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How are H+ ions secreted? What is their role outside of the cell?
H+ secretion mainly by H+ATPase (minor role of K+H+ATPase). Excreted as free H+ or buffered with HPO4(2-) -> H2PO4- & ammonia (NH3) -> ammonium (NH4+). Important in acid-base balance; net gain of blood HCO3- (not replacement for filtered HCO3-)
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Which hormones affect water & solute handling in late distal tubule/collecting duct? What affect do they have?
Aldosterone: increases Na+ reabsorption, K+ secretion & H+ secretion. ANP: decreases Na+ reabsorption. ADH: increase H2O reabsorption & increases urea reabsorption
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Where and how does aldosterone enhance Na+ reabsorption? What happens in absence/excess aldosterone?
Principal cells: increases number/activity of apical Na channels & increases activity of basolateral Na pump. Absence -> kidneys excrete excessive Na+. Excess -> too little Na+ excretion -> Na+ retention -> expansion of extracellular fluid volume
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Where and how does aldosterone enhance K+ reabsorption?
Principal cells: increases number & activity of apical K+ channels, increases activity of basolateral Na+ pump and increases Na+ reabsorption
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Where are H+ ions secreted? How does aldosterone enhance H+ secretion?
Intercalated cells. Aldosterone stimulates H+ATPase pump
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What are the consequences of disturbed aldosterone levels?
Primary (adrenal carcinoma) & secondary (volume depletion) hyperaldosteronism -> metabolic alkalosis & hypokalaemia (increased urinary excretion of K -> hypertension, oedema). Hypoaldosteronism -> hyperkalaemia -> muscle weakness & paralysis
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What does ADH do? What is the result of ADH being absent or present?
ADH facilitates H2O reabsorption: fluid is hyposmotic to plasma, ADH increases permeability. ADH absent: diuresis (dilute urine). ADH present: anitdiuresis (insertion of AQP2, water exits by osmosis, concentrates urine). ADH regulating ECF osmolality
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What effect does ADH have on permeability of inner medullary collecting duct (IMCD) to urea?
Increases permeability: ADH-dependent, facilitated diffusion urea transporter (UT1) in IMCD. H2O reabsorption concentrates urea, diffuses into medullary interstitium (maintain osmotic gradient), urea diffuses in des/ascending limbs -> urea recycling
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What effect does diuresis & antidiuresis have on [urea]?
Diuresis: increased urine volume -> lumen [urea] low. Antidiuresis: decreased urine volume -> lumen [urea] high
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Give examples of disorders of ADH secretion or response
Diabetes insipidus: central (inadequate secretion) or nephrogenic (tubule insensitivity), tubule impermeable to H2O, large vol dilute urine (polyuria). SIADH: excess H2O reabsorbed -> hyponatraemia. Nocturnal enuresis/bed-wetting: increased night ADH
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Other cards in this set

Card 2

Front

What movement happens in the ascending limb?

Back

Impermeable to water, ~20-30% of Na+, Cl- & K+ reabsorbed. Little reabsoprtion happens in the thin ascending limb (passive), most reabsorption happens in the thick ascending limb

Card 3

Front

What ion movement happens in the thick ascending limb?

Back

Preview of the front of card 3

Card 4

Front

How else do sodium ions enter cells in the thick ascending limb?

Back

Preview of the front of card 4

Card 5

Front

In thick limb, active transport of NaCl is not accompanied by water. What does this result in?

Back

Preview of the front of card 5
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