Tubular function 2 Flashcards
Is filtrate hyper, hypo, or isosmotic with plasma after passing PCT?
Isosmotic
goes into loop of henle
Which limb of Loop of Henle is permeable to water? What is the aquaporin channel responsible?
Descending thin limb
AQP1
Descending limb is less permeable to what 2 molecules?
NaCl and urea
What is reabsorbed in ascending limb? 3 molecules.
Na+, Cl- and K+
Thin ascending limb – passive? Active? How much?
Passive
little reabsorption
mostly Na+
The protein channel that transports 3 molecules? Where do they go? Which membrane are they located on?
Symporter protein, located on apical membrane.
Go into cell.
How does Cl- leave the cell?
Passive diffusion through basolateral Cl- channels
About how much (Minority/majority?) of K+ leaves the cell. To which side? How? What effect does this have?
Majority leaks back into lumen via apical K+ channels.
Tubular lumen becomes +ve charge
Drives paracellular diffusion of Na+, Ca2+ and Mg2+
How does Na+ leave the cells?
Sodium pump via electrochemical gradient
What are 2 consequences of the ascending loop of Henle being impermeable to water?
Osmolality of tubular fluid will decrease (solutes removed but water can’t move with it - more water in tubular fluid)
Interstitual fluid gets more concentrated (hyperosmotic)
Which protein channel do loop diuretics work on?
Sodium comes in by co-transport with K+ and 2Cl- (sodium pump?)
Is the interstitial fluid of medulla hyper, iso, or hypoosmotic as a result of the actions of the ascending limb of loop of henle? What is the effect of this?
Filtrate entering the DCT is now hyper, hypo, or isosmotic?
Hypoosmotic when it enters the DCT (more dilute)
What happens in the early DCT?
What are the ions involved?
Continues active dilution
Impermeable to water
Na+, Cl-, Ca2+, Mg2+, K+, H+
Which protein channel do Thiazides act on?
Sodium and chloride symporter proteins
What are 2 buffer naturally present in the luminal fluid?
DCT
HPO42- or NH3
What are 2 cells present on the late DCT? What do each of them do?
Principle cells - reabsorb Na+ and water, secrete K+
Intercalated cells - secrete H+, reabsorb HCO3- and K+
What are 3 hormones that regulate kidney function? What do each of them do?
Aldosterone: INCREASE Na+ reabsorption, K+ and H+ secretion
ANP: DECREASE Na+ reabsorption
ADH/vasopressin: INCREASE H2O and urea reabsorption
Where is aldosterone secreted from?
From zona glomerulosa of adrenal cortex
Explain the 3 functions of Aldosterone
- Enhances Na+ reabsorption - inc number and activity of apical Na+ channels, and activity of basolateral Na+ pump.
- Enhances K+ secretion in principal cells: Inc, number and activity of apical K+channels, basolateral Na+ pump and Na+ reabsorption
- Enhances H+ secretion in intercalated cells - stimulates H+ATPase pump.
Is the DCT and Collecting duct naturally permeable or less permeable to water?
naturally less permeable
What does ADH do? Which aquaporin does it stimulate?
facilitates reabsorption of water
activates AQP2
Explain the biochemical pathway of ADH action. What is the secondary messenger?
acts on receptors in basolateral membrane
uses cAMP as secondary messenger to insert AQP2 on apical side
Where are AQP3 and 4 located?
basolateral membrane
What is the 2nd key role of ADH?
increases permeability of IMCD to urea (inner medullary collecting duct)
Normally, what parts of the nephron are permeable to urea?
proximal tubule and inner medulla
What is the name of the transporter than allows urea transport in the presence of ADH?
Urea transporter (UT1)
Urea recycling: which parts of the nephron does urea diffuse into?
eventually into descending and ascending lims of loop of henle
What are 3 disorders of ADH?
Diabetes insipidus (inadequate secretion or response to ADH -> polyuria, polydipsia)
SIADH (inappropriate secretion of ADH -> hyponatremia)
Nocturnal enuresis/bed-wetting (ADH secretion in circadian rhythm increases at night)
