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Physiology > Regulation of Extracellular Fluid Volume > Flashcards

Regulation of Extracellular Fluid Volume Flashcards

1
Q

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

A

Sodium

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2
Q

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

A

High sodium outside the cell

High potassium inside the cell

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3
Q

What happens to ECF volume when extracellular Na+ increases?

A

Increased ECF volume

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4
Q

Na excretion = ?

A

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

(GFR * [Na]plasma) = Na filtered

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5
Q

Describe a positive Na imbalance.

A

Na excreted < Na ingested

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6
Q

Describe a negative Na imbalance.

A

Na excreted > Na ingested

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7
Q

What two sensors control GFR and Na balance?

A

Extrarenal baroreceptors

Juxtaglomerular apparatus

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8
Q

What are the two extrinsic systems that control GFR?

A

Renal sympathetic nerves

Renin-angiotensin system

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9
Q

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

A

Increased renal arteriolar constriction

Decreased GFR

Increased filtration fraction

Increased reabsorption

Increased plasma volume

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10
Q

What is the effect of increased renin release?

A

Increased plasma AngII

Decreased GFR

Decreased RBF

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11
Q

Tubular reabsorption is regulated by? (5)

A

Aldosterone

Renal sympathetic nerves

Angiotensin II

ANP

ADH

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12
Q

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

A

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

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13
Q

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

A

ACTH

Increased plasma potassium

Angiotensin II

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14
Q

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

A

Stimulates aldosterone secretion

Increases Na reabsorption

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15
Q

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

A

Direct action on β1-receptors of granular cells

Stimulates Na reabsorption in proximal tubules

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16
Q

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

A

Constriction of arterioles decreases RBF

Decreased PPTC

Increase πPTC

Increases Na reabsorption

17
Q

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

A

Stimulate Na reabsorption by stimulating Na-H exchanger

18
Q

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

A

Increases filtration fraction

Increases Na and water reabsorption in proximal tubule

19
Q

What effect does angiotensin II have on aldosterone secretion?

A

Increases aldosterone secretion.

20
Q

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

A

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*

21
Q

Water excreted = ?

A

Water excreted = GFR - Volume of water reabsorbed

22
Q

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

A

ADH levels

Baroreceptors and/or osmoreceptors

23
Q

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

A

Increases permeability of collecting ducts to water

Decreases water excretion by increasing the number of aquaporin channels

24
Q

How do baroreceptors control ADH secretion?

A

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

25
Q

How do osmoreceptors control ADH secretion?

A

They sense osmolarity and stimulate secretion of ADH accordingly

26
Q

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

A

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

27
Q

Where are the centers that mediate thirst located?

A

Hypothalamus

28
Q

What effects does angiotensin II have on the thirst response?

A

Stimulates thirst

Stimulates ADH release to increase water reabsorption

29
Q

What is euvolemia?

A

Normal ECF volume

30
Q

Describe Glomerulotubular balance (GTB).

A

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

31
Q

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

A

10%

90% reabsorbed

32
Q

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

A

closely matches the amount ingested in the diet

33
Q

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

A

Autoregulation

GTB

Sympathetic stimulation

Angiotensin II

Local metabolites (prostaglandins, NO, dopamine)

34
Q

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

A

Decreased renal perfusion pressures

Decreased GFR

Increased renin-angiotensin-aldosterone system

Increased sympathetic stimulation

35
Q

What is hyponatremia?

A

Low blood sodium

< 135 mEq/L

< 275 mOsm/L

36
Q

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

A

Hyponatremia caused by increased ADH secretion

37
Q

What is hypernatremia?

A

High blood sodium

> 145 mEq/L

> 295 mOsm/L

38
Q

Describe central diabetes insipidus. Cause? Effect?

A

Decreased ADH secretion from the posterior pituitary

Results in massive outputs of hypoosmotic urine and hypernatremia

39
Q

Describe nephrogenic diabetes insipidus. Cause? Effect?

A

Normal ADH, but tubules do not respond to it

Results in hypoosmotic urinary output and hypernatremia

Physiology (11 decks)

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