Regulation of Water and Osmolality

Question 1

Are salt and water regulation by the kidney dependent or independent of each other

Answer 1

Independent

Question 2

Sodium regulation determines ___

Water regulation determines ___

Answer 2

Na: ECF volume

WaterL body osmolality

Question 3

What is the tonicity in the medullary interstitium? (hyper, iso, hypo)

Answer 3

Hypertonic

Allows us to concentrate our urine

Question 4

Tonicity

Answer 4

Effective plasma osmolality
Refers to the ability of the solution to actually influence the movement of water across the cell membrane
(ECF solute + ICF solute)/Total body water

Question 5

Normal osmolality of Na

Answer 5

285-290 mosm/kg

Question 6

Are disorders of plasma osmolality normally due to abnormalities of water or Na?

Answer 6

Water! 99% of the time

Abnormalities in Na handling may co-exist

Question 7

Body compartment volume disorders are usually due to water or Na?

Answer 7

Na

Question 8

Insensible losses

Answer 8

Any way of losing fluids that is not the urine

Ex: skin, membranes, lungs, feces

Question 9

Vasa recta

Answer 9

Major blood vessels that carry blood into and out of the renal medulla
Flow in the opposite direction as urine

Question 10

Countercurrent exchange

Answer 10

Urine and blood flow in opposite directions

Promotes exchange of solutes and water to preserve medullary interstitial hypertonicity

Question 11

2 requirements for forming concentrated urine

Answer 11

Hypertonic medullary interstitium

High levels of ADH

Question 12

4 factors that contribute to the excess buildup of solute in the interstitium

Answer 12

Thick ascending LoH (active transport of Na out)
Collecting ducts (active transport of Na out)
Passive urea diffusion/recycling
Diffusion of only a small amount of water fro medullary tubules into interstitium

Question 13

Main function of

1. Descending LoH
2. Ascending LoH

Answer 13

1. Concentration of filtrate

2. Dilution of filtrate

Question 14

Urea

Answer 14

Also helps to generate the hypertonic medullary interstitium
It is passively reabsorbed from the tubule
Recirculation between the CD and the LoH
When ADH is present, more urea is reabsorbed from the inner medullary CDs

Question 15

2 features of the renal medullary blood flow that prevent the countercurrent multiplier system from dissipating

Answer 15

Medullary blood flow is low

Vasa recta serve as countercurrent exchangers

Question 16

Plasma osmolarity is regulated by 2 main systems

Answer 16

Osmoreceptor-ADH system

Thirst mechanism

Question 17

ADH is released in response to which 2 stimuli

Answer 17

Change in plasma osmolarity (detected by osmoreceptors in anterior hypothalamus)
Change in BP or in blood volume (detected by arterial baroreceptors and atrial stretch receptors)

Question 18

How does an increase in plasma osmolarity cause ADH release?

Answer 18

Increase in the osmolarity causes osmoreceptors to shrink
Initiates an AP that eventually gets to the posterior pituitary
Stimulates an influx of Ca ions causing a release of ADH from secretory granules
Signals from the osmoreceptors also induce the thirst mechanism

Question 19

2 places where ADH increases water permeability

Answer 19

Late distal tubules

Cortical and inner medullary collecting ducts

Question 20

How does
1. Decreased BP/volume
2. Increased blood volume
influence ADH release?

Answer 20

1. Detected by arterial baroreceptors, stimulate ADH release

2. Detected by cardiopulmonary reflexes (atrial stretch receptors), decrease ADH release, stimulate ANP release

Question 21

How is water reabsorbed?

Answer 21

In the presence of ADH
Passive diffusion through aquaporin channels down an osmotic gradient
Without ADH the collecting duct is impermeable to water

Question 22

What is the obligatory urine volume?

Answer 22

0.5L/day

Minimal volume of water needed to excrete ingested and waste produced osmoles