Regulation of Extracellular Fluid Volume

Question 1

Maintainance of body fluid volume is closely tied to regulation body ______ content.

Answer 1

Sodium

Question 2

The Na-K-ATPase pump maintains a high sodium concentration _____ the cell and a high potassium concentration _______ the cell.

Answer 2

High sodium outside the cell

High potassium inside the cell

Question 3

What happens to ECF volume when extracellular Na+ increases?

Answer 3

Increased ECF volume

Question 4

Na excretion = ?

Answer 4

Na excreted = (GFR * [Na]_plasma) - Na reabsorbed

(GFR * [Na]_plasma) = Na filtered

Question 5

Describe a positive Na imbalance.

Answer 5

Na excreted < Na ingested

Question 6

Describe a negative Na imbalance.

Answer 6

Na excreted > Na ingested

Question 7

What two sensors control GFR and Na balance?

Answer 7

Extrarenal baroreceptors

Juxtaglomerular apparatus

Question 8

What are the two extrinsic systems that control GFR?

Answer 8

Renal sympathetic nerves

Renin-angiotensin system

Question 9

What is the effect of increasing renal sympathetic nerve activation? (5)

Answer 9

Increased renal arteriolar constriction

Decreased GFR

Increased filtration fraction

Increased reabsorption

Increased plasma volume

Question 10

What is the effect of increased renin release?

Answer 10

Increased plasma AngII

Decreased GFR

Decreased RBF

Question 11

Tubular reabsorption is regulated by? (5)

Answer 11

Aldosterone

Renal sympathetic nerves

Angiotensin II

ANP

ADH

Question 12

How does aldosterone act on the kidney? What cellular changes occur?

Answer 12

Binds to intracellular receptors

Increases number of luminal-membrane sodium channels as well as basolateral Na-K-ATPase pumps in the cortical collecting duct (principal cells)

Increases ATP synthesis

Question 13

What are the three major inputs to the adrenal gland that stimulate aldosterone secretion?

Answer 13

ACTH

Increased plasma potassium

Angiotensin II

Question 14

Does hemorrhage inhibit or stimulate aldosterone secretion? Does this lead to an increase or decrease in Na reabsorption?

Answer 14

Stimulates aldosterone secretion

Increases Na reabsorption

Question 15

How do renal sympathetic nerves stimulate renin secretion? What direct effect does this have?

Answer 15

Direct action on β1-receptors of granular cells

Stimulates Na reabsorption in proximal tubules

Question 16

How do renal sympathetic nerves affect filtration fraction and peritubular capillary Starling forces?

Answer 16

Constriction of arterioles decreases RBF

Decreased P_PTC

Increase π_PTC

Increases Na reabsorption

Question 17

What is the direct effect of angiotensin II on proximal tubule cells?

Answer 17

Stimulate Na reabsorption by stimulating Na-H exchanger

Question 18

What effects does angiotensin II have on filtration fraction and peritubular capillary Starling forces?

Answer 18

Increases filtration fraction

Increases Na and water reabsorption in proximal tubule

Question 19

What effect does angiotensin II have on aldosterone secretion?

Answer 19

Increases aldosterone secretion.

Question 20

Describe atrial natriuretic peptide (ANP). Where is it made? Function?

Answer 20

A peptide hormone secreted by cardiac atrial cells; released during distention of the atria

Inhibits sodium reabsorption by increasing cGMP (inhibits Na channels)

*evolutionary remnant; cannot overcome effects of Angiotensin II*

Question 21

Water excreted = ?

Answer 21

Water excreted = GFR - Volume of water reabsorbed

Question 22

What is the main determinant of water excretion? What is it secreted by?

Answer 22

ADH levels

Baroreceptors and/or osmoreceptors

Question 23

What is the major function of antidiuretic hormone (ADH)? How does this affect water excretion?

Answer 23

Increases permeability of collecting ducts to water

Decreases water excretion by increasing the number of aquaporin channels

Question 24

How do baroreceptors control ADH secretion?

Answer 24

When blood plasma volume decreases, less firing of baroreceptors occurs, which stimulates ADH secretion by the posterior pituitary gland

Question 25

How do osmoreceptors control ADH secretion?

Answer 25

They sense osmolarity and stimulate secretion of ADH accordingly

Question 26

Why is a thirst response necessary when the kidneys are able to reabsorb a majority of the 180 L/day they secrete?

Answer 26

Reabsorption of water alone cannot restore total body water to normal levels, which can only be achieved by increasing water intake.

Question 27

Where are the centers that mediate thirst located?

Answer 27

Hypothalamus

Question 28

What effects does angiotensin II have on the thirst response?

Answer 28

Stimulates thirst Stimulates ADH release to increase water reabsorption

Question 29

What is **euvolemia**?

Answer 29

Normal ECF volume

Question 30

Describe **Glomerulotubular balance (GTB)**.

Answer 30

The ability of each successive segment of the proximal tubule to reabsorb a constant fraction of glomerular filtrate and solutes delivered to it

Question 31

How much Na initially filtered actually makes it to the distal tubule?

Answer 31

**10%** 90% reabsorbed

Question 32

Na reabsorption in the distal tubule and collecting duct is regulated so that amount excreted in urine \_\_\_\_\_.

Answer 32

closely matches the amount ingested in the diet

Question 33

What five mechanisms maintain constant Na delivery to the distal tubule (during euvolemia)?

Answer 33

Autoregulation GTB Sympathetic stimulation Angiotensin II Local metabolites (prostaglandins, NO, dopamine)

Question 34

What happens to renal function in patients with congestive heart failure? (4)

Answer 34

Decreased renal perfusion pressures Decreased GFR Increased renin-angiotensin-aldosterone system Increased sympathetic stimulation

Question 35

What is hyponatremia?

Answer 35

Low blood sodium \< 135 mEq/L \< 275 mOsm/L

Question 36

Describe **syndrome of inappropriate ADH secretion (SIADH)**. What is it caused by?

Answer 36

Hyponatremia caused by increased ADH secretion

Question 37

What is **hypernatremia**?

Answer 37

High blood sodium \> 145 mEq/L \> 295 mOsm/L

Question 38

Describe **central diabetes insipidus**. Cause? Effect?

Answer 38

Decreased ADH secretion from the posterior pituitary Results in massive outputs of hypoosmotic urine and hypernatremia

Question 39

Describe **nephrogenic diabetes insipidus**. Cause? Effect?

Answer 39

Normal ADH, but tubules do not respond to it Results in hypoosmotic urinary output and hypernatremia