Lecture 17 - Urine [ ] & Dilution

Question 1

What is the major function of the kidney?

Answer 1

To control ECF Osmolarity

Question 2

What segment is described by the following?

Active NaCl transport, highly permeable to water, permeable to NaCl and urea

A. PCT
B. Thin descending limb of LoH
C. Thin ascending limb of LoH
D. Thick ascending limb of LoH
E. DCT
F. Cortical collecting tubule
G. Medullary collecting duct

Answer 2

A. PCT

Question 3

Water excreted by kidneys when excess water exists. 
A. 10 L/day
B. 20 L/day
C. 30 L/day
D. 40 L/day

Answer 3

B. 20 L/day

Question 4

Region of the nephron impermeable to water under all circumstances.

A. PCT
B. Desc limb of Loop of Henle
C. Ascending limb of loop of Henle
D. Distal Convoluted Tubule

Answer 4

C. Ascending limb of loop of Henle

Question 5

The _______ has numerous NaCl transporters that utilize active transport.

A. PCT
B. Thin descending Loop
C. Thick ascending Loop
D. DCT

Answer 5

C. Thick ascending Loop

Question 6

Concentrated urine formation occurs in the _______ in the presence of ________.

A. Loop of Henle; ADH
B. Loop of Henle, PTH
C. DCT; ADH
D. DCT; PTH

Answer 6

C. DCT; ADH

ADH acts here to increase resorption of water. This results in an increase in urine Osmolarity. Osm=[solute]/[H2O]

Question 7

ADH regulates the reabsorption of water in the ______.

Answer 7

Distal convoluted tubule

Question 8

The thick ascending limb of the Loop of Henle is impermeable to water. What does this do to the osmolarity of tubular fluid and how is this accomplished?

Answer 8

Becomes more dilute; the thick ascending limb sees many solutes being reabsorbed and no permeability to water (lowers osmolarity overall); ADH does not act here

Question 9

ADH acts upon the ______ causing water _____

Answer 9

DCT; reabsorption

Question 10

What is the maximum urine concentration possible?

a. 1000-1200 mOsm/L
b. 1200-1400 mOsm/L
c. 1400-1600 mOsm/L
d. 1500-1800 mOsm/L

Answer 10

B. 1200-1400 mOsm/L

Question 11

What is required for the formation of a concentrated urine?

Answer 11

1) Presence of ADH (allows for reabsorption of water at the DCT increasing tubular osmolarity)
2) High osmolarity of renal medullary interstitial tubule (allows for cross current multiplication)

Question 12

mOsm of solutes that must be excreted each day to maintain normal mOsm of blood.

Answer 12

600 mOsm/day

Question 13

Obligatory urine volume

Answer 13

0.5 L/day

Question 14

65% of filtered electrolytes are reabsorbed in the _______

A. PCT
B. DCT
C. Ascending Loop
D. Medullary collecting duct

Answer 14

A. PCT

Question 15

What regions of the nephron are highly permeable to water?

Answer 15

PCT; desc. loop of Henle

In the presence of ADH - late DCT and cortical collecting tubule

Question 16

Describe the countercurrent multiplier system:

Answer 16

1) Iso-osmotic fluid in the PCT
2) Active resorption of NaCl by the ascending loop of Henle increased interstitial fluid osmolarity
3) Increased osmolarity pulls water from the permeable descending loop of Henle
4) Fluid is “pushed” through the system, and continues steps 1-3 until the tubular fluid is highly [ ] in the Loop of Henle, and the DCT is hypotonic

Question 17

Urea is important in the establishment of interstitial osmolarity. Which regions of the nephron are impermeable to urea?

Answer 17

Cortical collecting tubule

Question 18

Urea permeability is determined by UT-A1 and UT-A3 receptor expression. These transporters are induced by what hormone? Where are these transporters located?

Answer 18

ADH; medullary collecting duct

Question 19

What other compound follows water out of the medullary collecting ducts?

Answer 19

Water; this causes a concentration of urine in the medullary collecting ducts, in the presence of ADH

*Note as to WHY this is important:

ADH will cause the late DCT to resorb water, which should concentrate the urine. Urea “pulls” water out of the medullar collecting ducts, which concentrates the urine further. *

Question 20

Increased osmolarity of ECF will cause the shrinking of ______.

Answer 20

Osmoreceptor cells in the anterior vicinity of 3rd ventricle (AV3V)

Question 21

Shrinkage of osmoreceptor cells in the hypothalamus results in release of ____ from what two regions?

Answer 21

ADH;
supraoptic nuclei;
paraventricular nuclei