Urinary Concentration And Dilution

Question 1

In the Loop of Henle, is sodium reabsorbed actively or passively?

Answer 1

Actively

Question 2

In the loop of henle, is water reabsorbed actively or passively?

Answer 2

Passively, solute linked

Question 3

What is the counter current multiplier?

Answer 3

Its a large gradient of increasing osmolarity in the interstitial fluid down the descending loop of henle, and then decreasing osmolarity along the length of the ascending loop of henle

(Runs from the corticomedullary border to the tip of the papilla)

Question 4

In the descending limb of the LOH, what is entering/leaving the lumen?

Answer 4

TONS of water is leaving the lumen due to the very high osmolarity of the interstitium and the presence of many aquaporins

(NO active transport of NaCl)

Question 5

Which is more permeable to water:

Descending limb or ascending limb

Answer 5

Descending by far

Question 6

Is the ascending limb permeable to water?

Answer 6

No

Question 7

Does the ascending limb reabsorb NaCl actively or passively?

Answer 7

Actively

Question 8

Where is the urine most concentrated in the loop of henle?

Answer 8

At the bottom (1200 mOsm)

Question 9

Why is urine get progressively more dilute along the ascending limb?

Answer 9

Due to ions getting actively transported into the ISF

Question 10

What is the largest osmotic gradient that can be maintained across the wall of the ascending limb?

Answer 10

200 mOsm

Question 11

What is the essential component of the countercurrent multiplier?

Answer 11

ACTIVE TRANSPORT***

Question 12

What transporter is blocked by Lasix?

Answer 12

the NKCC2 cotransporter in the thick ascending limb

Prevents reabsorption of Na+, 2Cl-, and K+, so they will stay in the urine

Question 13

What transporter is stimulated by ADH?

Answer 13

NKCC2 in the ascending limb

Question 14

What happens to the blood in the vasa recta as it flows down the hairpin loop?

Answer 14

NaCl diffuses into the blood

Water diffuses out

(Blood gets more concentrated)

Question 15

What happens to the blood in the vasa recta as it come up the hairpin loop?

Answer 15

NaCl diffuses out

Water diffuses in

(Blood gets more dilute)

Question 16

What is the effect of the blood in the vasa recta getting more concentrated as it descends and more dilute as it ascend?

Answer 16

Protects the ISF gradient (countercurrent multiplier)

Question 17

As blood in the vasa recta gets more concentrated and then more dilute, is there active transport?

Answer 17

No, the entire process is entirely passive. Diffusion only

(Descending: salt in, water out

Ascending: salt out, water in)

Question 18

What controls the permeability of the collecting duct to urea?

Answer 18

ADH

Which means that without ADH you can’t concentrate urine well

Question 19

Where is urea recycled?

Answer 19

In the medulla of the kidneys

Watch the osmosis video for this

Question 20

What happens to the urine when it gets to the Early DCT?

Answer 20

The NCC transporter reabsorbs NaCl

No water is moving in/out, so the urine gets DILUTED

Question 21

What transporter is affected by thiazide diuretics?

Answer 21

The NCC (NaCl) transporter in the early DCT

(Reason why thiazide diuretics are not as powerful as loop diuretics….this is in the cortex and does no contribute to the corticopapillary gradient)

Question 22

Is there an NKCC2 transporter in the Early DCT?

Answer 22

NO

Question 23

What are the 2 types of cells in the Late DCT and Collecting duct?

Answer 23

Principal Cells

α-Intercalated cells

Question 24

What do principal cells do?

Answer 24

Reabsorb Na+

Secrete K+

(Done via two separate channels: ENaC (epithelial Na channel) and then a K+ channel that doesn’t have a fun name)

Question 25

What kind of transporters are in principal cells?

Answer 25

ENaC (apical surface) reabsorbs

K+ channel for secretion (apical surface)

Na-K-ATPase (basal surface)

Question 26

What does aldosterone do?

Answer 26

Targets the Principal cells in the late DCT and Collecting duct: Increases the number of ENaC channels and increases the Na-K-ATPase activity

=increased Na+ reabsorption and increased K+ secretion

Question 27

What do the α-intercalated cells do?

Answer 27

Secrete H+ into the lumen (via H+ ATPase and H-K+ ATPase

Reabsorb K+

Question 28

What kind of transporters are in α-intercalated cells?

Answer 28

H+ ATPase (secretes H+)

H+, K+ ATPase (secretes one H+ and absorbs one K+)

Question 29

What controls the permeability of the collecting duct to water and urea?

Answer 29

ADH

Question 30

If there is no ADH, will water or urea leave the collecting duct?

Answer 30

No

Question 31

How does ADH increase water permeability in the collecting duct?

Answer 31

It causes the insertion of aquaporins into the apical membranes of CD cells

Question 32

If you are very dehydrated, a lot of water will be reabsorbed out of the collecting duct and late DCT. What 2 mechanisms allow this?

Answer 32

1. ADH made the aquaporins

2. Concentration gradient made by the Loop of Henle

Question 33

In the ascending limb of the LOH, is the urine hyperosmotic or hyposomotic?

Answer 33

Hyposmotic (slightly)

Question 34

In the early distal tubule, is the urine hyperosmotic or hyposmotic?

Answer 34

Hyposmotic

No water reabsorption in early DCT with some NaCl reabsorption

Question 35

In the late DCT and collecting ducts, Na+ reabsorption is regulated by ___________

Answer 35

Aldosterone

Question 36

In the presence of ADH, is urine hypersomotic or hyposmotic

Answer 36

Hyperosmotic

Question 37

What does amiloride do?

Answer 37

It blocks the ENaC channel in the late distal tubule and collecting duct.

(prevents the reabsorption of Na+)