Ch. 34 Berne and Levy: Control of Body Fluid Osmolality and Volume

Question 1

What are the 2 physiological regulators of ADH secretion?

Answer 1

1) osmolality of body fluids

2) volume and pressure of vascular system (hemodynamic)

Question 2

During diuresis, ADH activity and production is ______ (low or high)

Answer 2

low

Question 3

True or false: urea plays a major role in effecting ADH secretion

Answer 3

FALSE (urea is an ineffective osmole with respect to osmoreceptors)

Question 4

When plasma osmolality INCREASES, ADH synthesis _________

Answer 4

INCREASES (want to save water to bring that plasma osmolality down)

Question 5

What are the 3 actions of ADH?

Answer 5

1) INCREASE water permeability in the collecting duct
2) INCREASE medullary permeability of urea in collecting duct
3) stimulate NaCl reabsorption in the thick ascending limb and collecting duct

Question 6

How does ADH affect the urea cycle?

Answer 6

INCREASES permeability of terminal portion of the inner medullary collecting duct to urea (INCREASES reabsorption of urea to increase osmolality of medulla)

Question 7

True or False: fluid entering descending limb is isosmotic to plasma?

Answer 7

TRUE

Question 8

Rank sections of the kidney in order of lowest to highest osmolality: outer medulla, inner medulla, cortex

Answer 8

cortex < outer medulla < inner medulla

Question 9

What is known as the diluting segment and why is it called that?

Answer 9

the thick ascending limb - allows for active NaCl reabsorption

Question 10

True or False: fluid leaving thick ascending limb is isosmotic to plasma

Answer 10

FALSE; it is hyposmotic

Question 11

What effect do the distal tubule and collecting duct have on osmolality?

Answer 11

DECREASE it (further reabsorb NaCl)

Question 12

What establishes the hyperosmotic medullary interstitial gradient?

Answer 12

counter current multiplier

Question 13

Describe the steps that compromise the counter current multiplier

Answer 13

1) Water permeability of descending limb (passively moves out of tubule increasing osmo of tubular fluid)
2) Salt passively moves out of ascending limb, DT and CD

Question 14

Where is the site of highest osmolality in tubular fluid

Answer 14

bend of loop of Henle

Question 15

In the presence of ADH, what makes the urine concentrated, NaCl or urea?

Answer 15

urea

Question 16

How is the hyperosmotic gradient maintained during antidiuresis when water is reabsorbed?

Answer 16

water is reabsorbed mostly from the cortex > outer medulla > inner medulla

Question 17

What are the two most abundant species in the medulla?

Answer 17

NaCl and urea

Question 18

Where is the only place along the nephron where urea can enter?

Answer 18

Descending limb of loop

Question 19

Why is urea an ineffective osmole when it comes to driving water reabsorption?

Answer 19

inner medullary collecting duct is highly permeable to urea (especially in presence of ADH)

Therefore, urea just equilibrates tubular conc to interstitual conc.

Question 20

Where does active salt pumping occur?

Answer 20

TAL, DT, CD

Question 21

What happens to urine flow as vasa recta flow increases?

Answer 21

INCREASES

Question 22

Which is greater, vasa recta water or salt?

Answer 22

salt

Question 23

What is negative free water clearance?

Answer 23

Uosm > Posm (trapped water, think of it as negative (ie very little) water in the urine)

Question 24

What are the 3 main chemical determinants of ECF osmolality?

Answer 24

Na, Cl, HCO3

Question 25

What is ECV?

Answer 25

effective circulating volume (portion of ECF within vascular system that is effectively perfusing tissues)

Question 26

What happens to ECV as arterial pressure and cardiac output increase?

Answer 26

INCREASES

Question 27

How do the low-pressure sensors work to detect effective circulating volume?

Answer 27

cardiac stretch receptors on the venous side of circulation detect increased stretching (more volume) and secrete ANP which induces natriuresis in cardiac atria and pulm vasculature

Question 28

When cardiac stretch receptors are activated, what happens to sympathetic stimulation?

Answer 28

DECREASES, ADH decreases, water diuresis

Question 29

Where are the high pressure sensors and how do they affect sympathetics?

Answer 29

aortic arch and carotid baroreceptors as well as JGA (detects slow tubular flow and decreases symp stim, increasing Na excretion) DECREASE sympathetics

Question 30

What are the other two sensors in addition to low and high pressure?

Answer 30

hepatic and CNS

Question 31

How does sympathetic stimulation affect Na reabsorption?

Answer 31

INCREASES it

Question 32

How does ANP affect GFR?

Answer 32

increases it (end goal of decreasing water and salt reabsorption to increase urine volume)

Question 33

What are the three efferent effectors regulating ECV?

Answer 33

Two salt retention 1) renal symp nerves 2) renin-angiotensin-aldosterone one salt excretion 3) ANP

Question 34

What are the 3 factors important in stimulating renin secretion?

Answer 34

1) Perfusion pressure (increase perf pres, decrease renin) 2) Symp nerve activity (increase symp, increase renin) 3) Delivery of NaCl to macula densa (increase NaCl delivery, decrease renin?)

Question 35

What is the enzymatic activity of renin?

Answer 35

converts angiotensinogen to AT1

Question 36

What converts AT1 to AT2?

Answer 36

ACE (angiotensin converting enzyme)

Question 37

What effect does AT2 have on ADH?

Answer 37

stimulates its release

Question 38

What effect does AT2 have on aldosterone?

Answer 38

INCREASES release from the adrenal cortex aldosterone then binds to receptors on the DT and CD and signals for production of new Na,K ATPase pumps which increases Na reabsorption and K+ secretion/excretion

Question 39

What stimuli effect the release of ANP?

Answer 39

1) INCREASED ECF 2) INCREASED AP (left atrial pressure) 3) INCREASED VP (right atrial pressure) basically, high pressure or too much volume (think, natriuertic wants to produce urine, wants to do that because there is too much volume)

Question 40

How does ANP secretion effect renin, ADH, Na excretion, symp stim?

Answer 40

decreases renin decreases ADH increases Na excretion decreases symps

Question 41

What is euvolemia?

Answer 41

Na intake matches excretion

Question 42

Where in the nephron does the 99% reabsorption of Na occur?

Answer 42

1) PT: 67% 2) TAL: 25% 3) DT: 4% 4) CD: 3%

Question 43

What are the 3 integrated responses of the nephron to INCREASED ECV?

Answer 43

1) increased GFR 2) decreased Na reabsorption in PT 3) decreased Na+ reabsorption in CD

Question 44

Why does an increase in ECV decrease Na reabsorption?

Answer 44

because Na in the interstitium pulls water and that continues to increase ECV

Question 45

What are the two most common causes of edema in terms of Starling forces?

Answer 45

1) increased hydrostatic pressure | 2) decreased oncotic pressure