Tubular function 2

Question 1

Is filtrate hyper, hypo, or isosmotic with plasma after passing PCT?

Answer 1

Isosmotic

goes into loop of henle

Question 2

Which limb of Loop of Henle is permeable to water? What is the aquaporin channel responsible?

Answer 2

Descending thin limb

AQP1

Question 3

Descending limb is less permeable to what 2 molecules?

Answer 3

NaCl and urea

Question 4

What is reabsorbed in ascending limb? 3 molecules.

Answer 4

Na+, Cl- and K+

Question 5

Thin ascending limb – passive? Active? How much?

Answer 5

Passive
little reabsorption
mostly Na+

Question 6

The protein channel that transports 3 molecules? Where do they go? Which membrane are they located on?

Answer 6

Symporter protein, located on apical membrane.

Go into cell.

Question 7

How does Cl- leave the cell?

Answer 7

Passive diffusion through basolateral Cl- channels

Question 8

About how much (Minority/majority?) of K+ leaves the cell. To which side? How? What effect does this have?

Answer 8

Majority leaks back into lumen via apical K+ channels.
Tubular lumen becomes +ve charge
Drives paracellular diffusion of Na+, Ca2+ and Mg2+

Question 9

How does Na+ leave the cells?

Answer 9

Sodium pump via electrochemical gradient

Question 10

What are 2 consequences of the ascending loop of Henle being impermeable to water?

Answer 10

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)

Question 11

Which protein channel do loop diuretics work on?

Answer 11

Sodium comes in by co-transport with K+ and 2Cl- (sodium pump?)

Question 12

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?

Answer 12

Hypoosmotic when it enters the DCT (more dilute)

Question 13

What happens in the early DCT?

What are the ions involved?

Answer 13

Continues active dilution
Impermeable to water
Na+, Cl-, Ca2+, Mg2+, K+, H+

Question 14

Which protein channel do Thiazides act on?

Answer 14

Sodium and chloride symporter proteins

Question 15

What are 2 buffer naturally present in the luminal fluid?

DCT

Answer 15

HPO42- or NH3

Question 16

What are 2 cells present on the late DCT? What do each of them do?

Answer 16

Principle cells - reabsorb Na+ and water, secrete K+

Intercalated cells - secrete H+, reabsorb HCO3- and K+

Question 17

What are 3 hormones that regulate kidney function? What do each of them do?

Answer 17

Aldosterone: INCREASE Na+ reabsorption, K+ and H+ secretion
ANP: DECREASE Na+ reabsorption
ADH/vasopressin: INCREASE H2O and urea reabsorption

Question 18

Where is aldosterone secreted from?

Answer 18

From zona glomerulosa of adrenal cortex

Question 19

Explain the 3 functions of Aldosterone

Answer 19

1. Enhances Na+ reabsorption - inc number and activity of apical Na+ channels, and activity of basolateral Na+ pump.
2. Enhances K+ secretion in principal cells: Inc, number and activity of apical K+channels, basolateral Na+ pump and Na+ reabsorption
3. Enhances H+ secretion in intercalated cells - stimulates H+ATPase pump.

Question 20

Is the DCT and Collecting duct naturally permeable or less permeable to water?

Answer 20

naturally less permeable

Question 21

What does ADH do? Which aquaporin does it stimulate?

Answer 21

facilitates reabsorption of water

activates AQP2

Question 22

Explain the biochemical pathway of ADH action. What is the secondary messenger?

Answer 22

acts on receptors in basolateral membrane

uses cAMP as secondary messenger to insert AQP2 on apical side

Question 23

Where are AQP3 and 4 located?

Answer 23

basolateral membrane

Question 24

What is the 2nd key role of ADH?

Answer 24

increases permeability of IMCD to urea (inner medullary collecting duct)

Question 25

Normally, what parts of the nephron are permeable to urea?

Answer 25

proximal tubule and inner medulla

Question 26

What is the name of the transporter than allows urea transport in the presence of ADH?

Answer 26

Urea transporter (UT1)

Question 27

Urea recycling: which parts of the nephron does urea diffuse into?

Answer 27

eventually into descending and ascending lims of loop of henle

Question 28

What are 3 disorders of ADH?

Answer 28

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)