Loop of Henle, Distal tubule & Collecting duct


HideShow resource information
  • 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
1 of 17
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
2 of 17
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
3 of 17
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
4 of 17
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)
5 of 17
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)
6 of 17
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+
7 of 17
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-)
8 of 17
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
9 of 17
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
10 of 17
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
11 of 17
Where are H+ ions secreted? How does aldosterone enhance H+ secretion?
Intercalated cells. Aldosterone stimulates H+ATPase pump
12 of 17
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
13 of 17
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
14 of 17
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
15 of 17
What effect does diuresis & antidiuresis have on [urea]?
Diuresis: increased urine volume -> lumen [urea] low. Antidiuresis: decreased urine volume -> lumen [urea] high
16 of 17
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
17 of 17

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
View more cards

Comments

No comments have yet been made

Similar Medicine resources:

See all Medicine resources »See all Kidney resources »