Water Balance

Question 1

What is the distribution of water in our bodies?

Answer 1

60/40/20. Meaning 60% of body weight is total body water. 40% of body weight is intracellular fluid. and 20% of body weight is extracellular fluid

Question 2

How is extracellular fluid subdivided?

Answer 2

3/4 –Interstitial and 1/4 –Plasma

Question 3

We lose some water via respiration and evaporation. What are these losses called? And how much are we actually loosing daily?

Answer 3

Insensible loss, apprx 700mL/day

Question 4

Abnormalities in plasma sodium concentration and osmolality generally reflect changes in the water balance/sodium balance?

Answer 4

Water balance!!!

Question 5

If there was a change in the sodium balance, what would you expect?

Answer 5

a change in the ECF volume

Question 6

Changes in _______________ regulate the secretion of ADH and/or Vasopressin and therefore urine flow.

Answer 6

Plasma Osmolality

Question 7

________ is 9 amino acid peptides that are rapidly degraded in the circulation. (Highlighted factoid)

Answer 7

ADH (AVP-vasopressin, same thing)

Question 8

If your plasma is hyperosmotic, will this trigger the secretion of ADH/AVP?

Answer 8

Yes.

(hyperosmotic = concentrated,and ADH/AVP will increase fluids)

Question 9

Under what circumstance might your body stop the secretion of ADH?

Answer 9

Hyposmotic plasma. Body has more fluid than solutes.

Question 10

Plasma Osmolality also controls thirst. Would you expect plasma to be hyperosmotic or hyposmotic if you felt thirsty?

Answer 10

HYPERosmotic

Question 11

What is the hierarchy for detection and management of osmotic control?

Answer 11

Osmolality changes of 1% are significant, and will be detected by the OSMORECEPTORS in the hypothalamus. Hypothalamus then signals the posterior pituitary to adjust ADH accordingly.

Question 12

ADH secretion is under control of what factors?

Answer 12

1) Osmolality
2) Blood pressure
3) Blood volume

Question 13

What are the mechanisms that makes ADH work to retain water?

Answer 13

1) ADH increases permeability of the distal tubule to water, so more is re-absorbed. It accomplishes this by inserting aquaporin into the apical membrane.
2) ADH increases permeability of collecting duct to urea (Urea deposits in the interstitium play a role in concentrating urine)
3) ADH increases NaCl transport which aids urinary concentration

Question 14

When do you get thirsty?

Answer 14

2-3% increase in plasma osmolality or decrease in blood pressure/volume

Question 15

Urine is concentrated in 2 ways, which are?

Answer 15

1) active reabsorption of NaCl

2) passive reabsorption of H20

Question 16

Where is NaCl being actively absorbed?

Answer 16

PCT, DCT, some in collecting duct. (also being passively reabsorbed in the ascending loop of Henle)

Question 17

Where is water being passively absorbed?

Answer 17

PCT, descending loop, collecting ducts

Question 18

what part of the kidney is most responsible for concentrating urine?

Answer 18

The loop of Henle. The longer the loop, the greater the countercurrent multiplication.

Question 19

Furosemide acts by inhibiting the Na/K/Cl transporter. What does this accomplish?

Answer 19

It abolishes the osmotic gradient of the interstitium, which prevents NaCl reabsorption (and therefore water reabsorption)

Question 20

What is the role of urea in urine concentration?

Answer 20

It is not absorbed until the end…the collecting ducts, where it is absorbed into the interstitium. This creates almost half the papillary osmolality.

Question 21

Why doesn’t the high concentration of urea dissipate into the vasa recta?

Answer 21

A portion does, but it is returned to the medulla by way of medullary recycling. (which takes urea from vasa recta and puts it right back in the interstitium)

Question 22

Water that is free of solutes is termed __________

Answer 22

free water

Question 23

Where is free water generated in our body?

Answer 23

The diluting segment of the kidney (aka the ascending limb of Henle and the distal tubule)

Question 24

True or False: Free water is always generated in the diluting segment, regardless of ADH

Answer 24

True

Question 25

If ADH has no effect on the generation of free water in the diluting segment, then what is it actually controlling?

Answer 25

The reabsorption of water

Question 26

Discuss the concept of free water clearance…and perhaps learn said calculation process

Answer 26

C(water) + C(osm) = V

C(water) = V - Cosm

Question 27

True/False: The nephron is impermeable to water without the presence of ADH

Answer 27

True

Question 28

What is the single effect?

Answer 28

reabsorption of solute to the exclusion of water. (mechanism behind the concurrent multiplier that concentrates urine)