Lecture 18 - Water and the Kidney

Question 1

What percentage of TBW is found in the ICF (within cells)?

Answer 1

66%

Question 2

What percentage of TBW is found in the ECF?

Answer 2

33%

Question 3

What does ECF consist of (including %)?

Answer 3

Interstitial fluid (between cells) 75%
Plasma (solution in blood) 20%
Transcellular (inside epithelial lined spaces) 5%

Question 4

What is the TBW in men vs women?

Answer 4

Men 60%
Women 55%

Question 5

Which parts of the nephron are permeable to water?

Answer 5

Proximal Tubule
Thin Descending - Limb of Loop of Henle
Late Distal Tubule*
Collecting Duct*
*Under influence of Vasopressin (AVP)/ Antidiuretic Hormone (ADH)

Question 6

Which parts of the nephron are not permeable to water?

Answer 6

Ascending Limb of Loop of Henle (Thin and Thick)
Early Distal Tubule (there is still debate about this)

Question 7

Which of the following statements is TRUE?
A. 65% of a male’s body is composed of water.
B. Normally, a person has 4 litres of plasma in their blood.
C. The net water intake and water output of person per day is 0.
D. A person can live without water for 3 months.

Answer 7

C. The net water intake and water output of person per
day is 0 - when at homeostasis

Question 8

What are aquaporins?

Answer 8

The aquaporin is a family of plasma membrane proteins that form channels that permit a high rate of water flow. They are specific to only water and they are impermeable to charged species.

Question 9

How much water is reabsorbed in the PT?

Answer 9

67% - 120L of H2O per day

Question 10

What epithelium is found in the PT?

Answer 10

Leaky absorptive epithelium

Question 11

What is the movement of water in the PT?

Answer 11

Paracellular and transcellular

Question 12

What AQP is found in leaky absorptive epithelium?

Answer 12

Aquaporin 1 (AQP1) which allows for the transcellular movement of water - present in both apical and basolateral membranes

Question 13

How much water does the Thin Descending Limbs - Loop of Henle reabsorb?

Answer 13

16% - 30L of H2O

Question 14

What epithelium is found in the thin descending limb of the loop of Henle?

Answer 14

Leaky absorptive epithelium

Question 15

How much water does the late distal tubules reabsorb?

Answer 15

5-10% - 10-20L of H2O

Question 16

What epithelium is found in the late distal tubules?

Answer 16

Tight absorptive epithelium

Question 17

How much water does the collecting ducts reabsorb?

Answer 17

approx 8%

Question 18

What epithelium is found in the CD?

Answer 18

Tight absorptive epithelium

Question 19

What is the distribution of AQP in the LDT and CD?

Answer 19

AQP2 in the apical membrane
AQP3 and AQP4 in the basolateral membrane

Question 20

Which AQP is under the regulation of AVP/ADH?

Answer 20

AQP2

Question 21

Describe AQP2

Answer 21

AQP2 is found in the apical membrane of the LDT and CD or in vesicles. When ADH is released, the AQP2 found in the vesicles are incorporated into the membrane.

Question 22

Which of the following statements is TRUE?
A. Aquaporins are only found in animals.
B. AQP2 is located on the apical membrane of Thick Ascending limb cells.
C. AQP3 is located in the basolateral membrane of collecting duct cells.
D. An osmotic gradient is NOT required for water movement.

Answer 22

C. AQP3 is located in the basolateral membrane of collecting duct cells.

Question 23

Where is vasopressin (AVP)/anti-diuretic hormone (ADH) produced?

Answer 23

Produced in hypothalamus
- paraventricular nuclei
- supraoptic nuclei

Question 24

What is the stimulus of release of AVP?

Answer 24

Increased body osmolarity (osmoreceptors)
Decreased plasma volume (baroreceptor reflex)

Question 25

Where is AVP/ADH stored and released?

Answer 25

Stored and released from the posterior pituitary