Regulation of Water Balance

Question 1

What is the relative blood pressure of a patient with renal failure? Why?

Answer 1

High because the kidney cannot excrete excess fluid

Question 2

What is insensible fluid loss?

Answer 2

Water lost through evaporation off the skin, or respiration

Question 3

What is the daily intake of water relative to the daily output?

Answer 3

Equal

Question 4

True or False: Kidneys control water excretion independently of Na+, K+, and urea

Answer 4

True

Question 5

On which surface of the proximal tubule cells is AQP1 expressed? How many molecules of water can be transported at once?

Answer 5

Both apical and BL membranes; 4 H2O

Question 6

Which part of the loop of Henle is permeable to water but impermeable to salt?

Answer 6

Thin descending limb

Question 7

Where are AQP3 and 4 expressed within the nephron?

Answer 7

Constitutive expression on the BL membrane of prinicipal cells of the collecting duct

Question 8

What are the two mechanisms of ADH secretion?

Answer 8

Osmoreceptors in the brain sense increases in plasma osmolarity; arterial baroreceptors detect increased MABP/ volume and signal to hypothalamus to release AVP

Question 9

Which of the two stimulatory mechanisms of ADH release is more sensitive? Which is more powerful?

Answer 9

Osmoreceptors are more sensitive but the volume receptors are more powerful

Question 10

Where and when is AQP2 expressed?

Answer 10

Expressed on the apical membrane of principal cells of the CD in response to ADH stimulation

Question 11

How does ADH stimulate AQP2 insertion into the membrane?

Answer 11

Binds to V2 receptor, which is a GsPCR– increased cAMP– phosphorylation of vesicles containing AQP2– exocytosis and fusion

Question 12

True or False: When circulating ADH levels fall there are signals for endocytic retrieval of AQP2 resulting in lysosomal degradation

Answer 12

False- no degradation

Question 13

How does AVP increase renal medullary interstitial osmolarity?

Answer 13

Increases urea reabsorption, and NaCl reabsorption

Question 14

What is the countercurrent mechanism?

Answer 14

The mechanism by which urine is concentrated

Question 15

What is the countercurrent mechansim dependent on?

Answer 15

Unique solute transport processes and specific anatomical arrangemet of loops of Henle and vasa recta

Question 16

What are the parts of the countercurrent system?

Answer 16

Countercurrent flow, countercurrent exchange, and countercurrent multiplication

Question 17

What is meant by countercurrent flow?

Answer 17

The movement of fluid and blood down the descending loop of Henle and vasa recta is opposite the movement of fluid/blood up the ascending LoH or vasa recta

Question 18

What is countercurrent exchange, and what is its purpose?

Answer 18

The passive diffusion of solutes and water in both directions across vasa recta capillary walls; restores isotonic plasma and maintains hyperosmotic medullary interstitium

Question 19

True or False: The ascending vasa recta carry away more water and solute than enters

Answer 19

True

Question 20

What determines how concentrated urine is?

Answer 20

The length of the Loop of Henle

Question 21

What are the countercurrent multipliers? What is the purpose?

Answer 21

The loops of Henle; establishes hyperosmotic medullary interstitium

Question 22

What physical characteristics allows the Loop of Henle to be the countercurrent multiplier?

Answer 22

The dtLoH is salt impermeable and water permeable and the TAL is H2O impermeable and salt permeable

Question 23

What is the driving force of H2O reabsorption in the tdLOH and CD?

Answer 23

Medullary ISF osmotic pressure

Question 24

What dictates the maximal urine concentration?

Answer 24

ISF osmolality

Question 25

What part of the nephron responds to ADH?

Answer 25

The collecting duct

Question 26

How is diuresis mediated following high water intake?

Answer 26

There will be low plasma [ADH] which means there will be little to no reabsorption in the collecting ducts

Question 27

What is the papillary Osm during diuresis relative to the Osm during antidiuresis?

Answer 27

During diuresis, the papillary Osm is ~ 1/2 of antidiuresis

Question 28

How is antidiuresis mediated following water restriction or severe sweating?

Answer 28

Low blood volume or high osmolarity will stimulate ADH release, increasing the permeability of the CD to H2O, facilitating its reabsorption

Question 29

Where is H2O and Na+ reabsorption dissociated?

Answer 29

In the CD

Question 30

How is the sensation of thirst mediated?

Answer 30

Increased plasma osmolarity or decreased plasma volume is detected and signaled to hypothalamus as with ADH release, specifically the hypothalamic thirst center; Additionally dry mouth and angiotensin II stimulate the hypothalamic thirst center

Question 31

How are changes in Na+ balance manifested and detected? Changes in H2O balance?

Answer 31

Changes in Na+ balance are manifested as changes in the ECF volume as measured by volume and pressor receptors; H2O balance manifests as chanegs in plasma osmolarity as measured by changes in plasma Na+

Question 32

What are the 3 mechanisms of diabetes insipidus? How does it present?

Answer 32

1) Deficiency in ADH, 2) Renal resistance to AVP, 3) Inappropriate excessive drinking; presents with polyuria (dilute), hypernatremia and polydipsia

Question 33

What is Syndrome of Inappropriate Antidiuretic Hormone Secretion?

Answer 33

Increase or excess release of ADH in absence of a physiologic stimulus

Question 34

How is SIADH treated?

Answer 34

Water restriction, V2R antagonist, diuretics