Lecture 9: Regulation of Water Balance and Body Fluid Osmolality (Bolsor)

Question 0

What does hypothalamus secrete to cause kidney to change body water content?

Answer 0

ADH

Question 1

what structures sense a change in blood pressure? What do they signal to effect a change in BP?

Answer 1

osmoreceptors and baroreceptors. Signal the hypothalamus to “make a decision” about whether an action is needed to regulate BP

Question 2

see flow charts pg. 82/83 scavma notes

Answer 2

:)

Question 3

what part of kidney does ADH act on?

Answer 3

late distal tubule and collecting ducts on the peritubular side

Question 4

What does ADH do specifically?

Answer 4

activates adenylate cyclase which causes insertion of water channels into the luminal membrane of the distal nephron

Question 5

2 main compartments of body fluid. Which is larger?

Answer 5

intracellular and extracellular. Intracellular compartment is larger

Question 6

How does body compensate when there is a loss of volume from the extracellular compartment?

Answer 6

Water moves into the extracellular compartment from the intracellular compartment to compensate for the loss. Therefore, hemorrage involves loss of volume from BOTH extracellular and intracellular compartments

Question 7

Primary controlling factor in how the kidney handles water

Answer 7

ADH

Question 8

Where is ADH stored? Where is it released?

Answer 8

Stored: posterior pituitary
Released: supraoptic nucleus projecting from the post. pituitary

Question 9

What happens if the thirst area of the hypothalamus has a lesion?

Answer 9

Animal will not have sensation to drink

Question 10

Most potent stimulus of ADH release

Answer 10

plasma osmolality. Increased plasma osmolality increases ADH release.

Question 11

What is unique about the osmoreceptors in the anterior wall of the third ventricle?

Answer 11

Area lacks a blood-brain barrier. These osmoreceptors signal plasma osmolality for ADH release

Question 12

How does blood volume effect ADH release?

Answer 12

Increased blood volume inhibits ADH secretion, decreased blood volume increases ADH secretion

Question 13

T or F: decreased blood volume elicits greater ADH amounts released than osmolality

Answer 13

T

Question 14

Where are sensory receptors responsive to blood volume located? How do they function?

Answer 14

atria and large veins. The receptors

Question 15

About how much blood loss (%) can be tolerated before large amts of ADH are release?

Answer 15

15%

Question 16

hyposmotic plasma –> thirst/intake of water

Answer 16

decreases

Question 17

hyperosmotic plasma –> thirst/intake of water

Answer 17

increases

Question 18

Once body water content is normalized, what happens to osmoreceptors and baroreceptors?

Answer 18

They stop signaling hypothalamus to make a change

Question 19

Where does ADH act?

Answer 19

peritubular side of late distal tubules and collecting ducts of kidney

Question 20

HOW does ADH act?

Answer 20

1) activates adenylate cyclase via a G protein mediated system on the basal membrane of collecting duct principal cells
2) triggers increased formation of cAMP
3) triggers cAMP-dependent protein kinase C to release vesicles with aquaporins that bind to apical membrane of cell. This ultimately increases water absorption from lumen of collecting duct into collecting duct principal cells.

Question 21

T or F: only the apical/luminal membrane of the collecting duct principal cells is variably permeable to water depending on how much ADH is present.

Answer 21

True. The basolateral membrane is not effected by ADH; its conductance of H2O is always high.

Question 22

Verney experiment: Explain what happens to urine flow if pituitary gland NOT removed (normal state) and 1) ingestion of H2O increases, 2) NaCl injected IA (into carotid a.) and 3) ADH injected IV

Answer 22

1) urine flow increases
2) urine flow decreases, even though the animal is not dehydrated
3) urine flow decreases, even though the animal is not dehydrated

Question 23

Verney experiment: Explain what happens to urine flow if pituitary gland is removed (abnormal state) and 1) ingestion of H2O increases, 2) NaCl injected IA (into carotid a.) and 3) ADH injected IV

Answer 23

1) urine flow increases
2) urine flow doesn’t change (normally it would decrease)
3) urine flow decreases (kidney was able to respond even though PP was removed)

Question 24

How do you differentiate primary polydipsic, hypothalamic, or nephrogenic causes for high urine flow in a patient?

Answer 24

Withhold water from the patient and measure urine osmolality with and without ADH:

• If urine osmolality goes up without adding ADH, animal is primary polydipsic (they have an excessive need to drink but can in fact concentrate urine normally; result of various disease states)
• If urine osmolality only goes up after ADH is added, animal’s problem is hypothalamic (in the hypothalamus) and the kidneys can only concentrate urine when ADH given
• If urine osmolality doesn’t go up at all even with addition of ADH, problem is nephrogenic (in the nephrons of the kidney)

see graph on bottom of p.85

Question 25

polyuria

Answer 25

excretion of large volumes of urine

Question 26

polydipsia

Answer 26

increased drinking

Question 27

polyuria and polydipsia may be due to 1 of 3 problems:

Answer 27

1) chronic and excessive fluid ingestion w/o a known cause
2) failure of the hypothalamic ADH secretory system
3) renal defect in H2O reabsorption