04a: Osmoregulation

Question 1

T/F: Normally, water is reabsorbed iso-osmotically at proximal tubule.

Answer 1

True

Question 2

ADH, secreted by (X), primarily affects (Na/water)-permeability in (Y) portion of tubule.

Answer 2

X = posterior pituitary;
Water;
Y = collecting duct

Question 3

High plasma ADH: you’d expect excretion of (high/low) volume of (dilute/concentrated) urine.

Answer 3

Low; concentrated

Question 4

About (X)% of water is reabsorbed in thick descending tubule.

Answer 4

X = 23

Question 5

Classic experiments of Verney demonstrated that plasma (hypo/hyper)-osmolality results in (X) with resultant (increase/decrease) of (Y).

Answer 5

Hyper-osmolality;
X = prompt secretion of ADH
Decrease;
Y = urine volume (with increase concentration)

Question 6

Creation of osmotic gradients occurs largely in which part of tubules? Why?

Answer 6

Ascending limb of loop of Henle;

Salt is actively reabsorbed, without transport of water

Question 7

The osmolality gradient is 200 mOsm at each level between which spaces?

Answer 7

Lumen of TAL (200 mOsm less) than interstitium and lumen of DL

Question 8

There’s a progressive (increase/decrease) in osmolality as tubular fluid flows downward toward hairpin loop. and (increase/decrease) in osmolality as it travels back upward.

Answer 8

Increase;

Decrease

Question 9

T/F: The osmolality in the inner medulla is primarily, 80%, due to Na.

Answer 9

False - mainly salt, but urea can contribute up to 50%

Question 10

A (low/high) protein diet is known to markedly depress renal concentrating ability due to (deficit/excess) in (X).

Answer 10

Low;
Deficiency;
X = urea

Question 11

T/F: Urea is a minor solute of voided urine, since large fraction undergoes medullary recycling.

Answer 11

False - major solute of voided urine, despite this recycling

Question 12

Medullary recycling of urea takes place in which tubule? The solute goes from (X) into (Y).

Answer 12

Inner medullary collecting duct;
X = IMCD
Y = interstitium THEN thin ascending loop of Henle

Question 13

During diuresis, (low/high) rate of water reabsorption results in (low/high) concentration of urea presented to terminal IMCD.

Answer 13

Low; low

Question 14

(X) enhances IMCD urea permeability. You’d expect this to be the result of (diuretic/antidiuretic) state.

Answer 14

X = ADH;

Antidiuretic (high urea concentration in IMCD)

Question 15

In (diuretic/antidiuretic) state, urea’s contribution to interstitial osmolality is greatest, nearly (X)%.

Answer 15

Antidiuretic (high ADH);

X = 50

Question 16

T/F: In the absence of ADH, the distal tubules and collecting ducts are impermeable to water.

Answer 16

True

Question 17

Per day, the two extremes of total urine output are (X) in diuresis state and (Y) in antidiuresis state.

Answer 17

X = 18 L (10% GFR) of 50 mOsm conc
Y = 0.4 L of 1200 mOsm conc

Question 18

In brief, ADH binds (lumenal/basolateral) receptors that lead to (X) (activation/inhibition) which causes (increase/decrease) in (Y) formation.

Answer 18

Basolateral;
X = AC
Activation;
Increase;
Y = cAMP

Question 19

In high ADH state, how does (increase/decrease) in cAMP alter collecting duct permeability?

Answer 19

Increase;

Phosphorylates lumenal membrane proteins that leads to increased aquaporin incorporation in lumenal membranes

Question 20

T/F: ADH’s effects are confined to collecting duct permeability.

Answer 20

False - also acts on ascending limb Na transport and vasa recta blood flow

Question 21

High ADH state: TAL Na transport would (increase/decrease) and vasa recta blood flow would (increase/decrease). Provide brief explanations.

Answer 21

Increase (facilitates water reabsorption by increasing interstitial osmolality);
decrease (reduce washout of interstitial solute)

Question 22

Blood flow through the medulla tends to dissipate interstitial osmolality gradients. (X) phenomenon between (Y) structures counteracts this.

Answer 22

X = countercurrent exchange (of solutes and water)
Y = ascending and descending limbs of vasa recta

Question 23

ADH-secreting neurons receive (stimulatory/inhibitory) inputs from which main receptors? Star the more sensitive receptors.

Answer 23

1. Osmoreceptors (stimulatory)*

2. Baroreceptors and cardiopulmonary receptors (inhibitory)

Question 24

ADH: (osmo/baro)-receptors take precedent if there’s large change in (osmolality/volume). This could lead to (X) value that’s well below normal.

Answer 24

Baroreceptors;
Volume (greater 10% depletion);
X = osmolality

Question 25

(Renin/AII/ANP) directly (stimulates/inhibits) ADH secretion.

Answer 25

AII stimulates; ANP inhibits

Question 26

T/F: Osmoreceptors can be found in nearly all arterioles.

Answer 26

False - osmoreceptors are nearposterior pituitary neurons

Question 27

T/F: Osmolality is the chief factor regulating secretion of ADH.

Answer 27

True

Question 28

Oxidative metabolism contributes to our water (input/output).

Answer 28

Input

Question 29

AQP1 present at (lumenal/basolateral) membranes of which duct?

Answer 29

Both; PT

Question 30

T/F: Some aquaporins are present independently of ADH.

Answer 30

True - AQP3 and 4

Question 31

Our obligatory water loss is around (X) per day.

Answer 31

X = 0.5 L

Question 32

Where are the JG cells anyway? They’re actually specialized (X) cells.

Answer 32

Afferent arteriole wall

X = smooth muscle