SM_197a: Water Balance and Urinary Concentration; Potassium Balance

Question 1

Describe the difference between osmoregulation and volume regulation

Answer 1

Question 2

Relative water excess is indicative of _____

Answer 2

Relative water excess is indicative of hyponatremia (low serum [Na⁺])

Question 3

Relative water deficit is indicative of ______

Answer 3

Relative water deficit is indicative of hypernatremia (high serum [Na⁺])

Question 4

Oliguria is ____ < urine < _____

Answer 4

Oliguria is 0.1 L/day < urine < 0.4 L/day

Question 5

Anuria is urine ____

Answer 5

Anuria is urine < 0.1 L/day

Question 6

Polyuria is urine _____

Answer 6

Polyuria is urine > 2.5-3.0 L/day

Question 7

_____ of ADH is required for urinary concentration

Answer 7

Stimulation of ADH is required for urinary concentration

Question 8

Urinary concentration via stimulation of ADH release involves _____, _____, and _____

Answer 8

Urinary concentration via stimulation of ADH release involves creation and maintenance of a hypertonic medullary interstitium, functional V2 vasopressin receptors on collecting duct cells, and functional aquaporin-2 water channels in collecting duct cells

Question 9

_____ of ADH release is required for urinary dilution

Answer 9

Suppression of ADH release is required for urinary dilution

Question 10

Urinary dilution via suppression of ADH release involves _____ and _____

Answer 10

Urinary dilution via suppression of ADH release involves adequate delivery of NaCl to thick ascending limb and separation of salt and water by the thick ascending limb

Question 11

Most water is reabsorbed in the _____ then the _____ of the nephron

Answer 11

Most water is reabsorbed in the proximal tubule then the thin descending limb of the loop of Henle of the nephron

Question 12

_____ and _____ of the nephron do not absorb water

Answer 12

Ascending limb and distal convoluted tubule do not absorb water

Question 13

_____ and _____ can absorb water if ADH is present

Answer 13

Cortical collecting duct and medullary collecting duct can absorb water if ADH is present

Question 14

Renal cortex is _____ with plasma

Answer 14

Renal cortex is isotonic with plasma (300 mOsm/kg H₂O)

Question 15

Outer medulla has ______

Answer 15

Outer medulla has mild hyperosmolality (300-4800 mOsm/kg H₂O)

Question 16

Inner medulla has ______

Answer 16

Inner medulla has strong hyperosmolality (480-1,200 mOsm/kg H₂O)

Question 17

Mechanisms allowing medullary hyperosmolality include ______, ______, and ______

Answer 17

Mechanisms allowing medullary hyperosmolality include countercurrent multiplier, urea cycling, and countercurrent exchange

• Countercurrent multiplier: establishes initial osmotic gradient
• Urea cycling: strengthens osmotic gradient
• Countercurrent exchange: maintains osmotic gradient

Question 18

______ establishes the intial osmotic gradient to allow for medullary hyperosmolality

Answer 18

Countercurrent multiplier establishes the intial osmotic gradient to allow for medullary hyperosmolality

Question 19

Steady state after the countercurrent multiplier occurs when interstitium osmolality is ______

Answer 19

Steady state after the countercurrent multiplier occurs when interstitium osmolality is 1,200 mOsm

Question 20

If ADH is present, water is reabsorbed in collecting duct which drives concentrations toward ______

Answer 20

If ADH is present, water is reabsorbed in collecting duct which drives concentrations toward osmotic equilibrium

Question 21

Trapping of _____ through a cycling mechanism strengthens the osmotic gradient for water reabsorption

Answer 21

Trapping of urea through a cycling mechanism strengthens the osmotic gradient for water reabsorption

Question 22

In counter current exchange in the peritubular capillaries, blood flows in the ______ direction of fluid in the loop of Henle, which maintains the ______

Answer 22

In counter current exchange in the peritubular capillaries, blood flows in the opposite direction of fluid in the loop of Henle, which maintains the counter current multiplier

Question 23

Medullary region is _____, so small changes in water or solute have a _____ impact on the medullary interstitium

Answer 23

Medullary region is small, so small changes in water or solute have a large impact on the medullary interstitium

Question 24

Mannitol _____ direct effect on tubular transport, but rather _____

Answer 24

Mannitol does not have a direct effect on tubular transport, but rather maintains osmolality of tubular fluid higher than it would be otherwise

Question 25

The higher the osmolality, the _____ the varopressin

Answer 25

The higher the osmolality, the higher the varopressin

(osmolality is main driving force for pituitary release of vasopressin)

Question 26

Vasopressin drives _____, which _____ osmolality

Answer 26

Vasopressin drives water reabsorption, which increases urine osmolality

Question 27

Volume depletion can ______ pituitary gland response to osmolality

Answer 27

Volume depletion can sensitize pituitary gland response to osmolality

(vasopressin will do less if more volume is depleted)

Question 28

Insertion of ______ into apical membrane allows water to pass into cells of the outer and inner medullary collecting duct

Answer 28

Insertion of aquaporin 2 into apical membrane allows water to pass into cells of the outer and inner medullary collecting duct

Question 29

Diabetes insipidus is when the nephron ______

Answer 29

Diabetes insipidus is when the nephron cannot reabsorb water

• Nephrogenic: insensitivity of kidneys to the effect of ADH
• Neurogenic: deficiency of ADH

Question 30

In internal K⁺ balance, factors promoting cell uptake of K⁺ include _____, _____, _____, and _____

Answer 30

In internal K⁺ balance, factors promoting cell uptake of K⁺ include Na⁺/K⁺ ATPase activity, insulin, catecholamines (beta-2 adrenergic receptors), and alkalosis

Question 31

In internal K⁺ balance, factors promoting cell efflux of K⁺ include ______, ______, ______, and ______

Answer 31

In internal K⁺ balance, factors promoting cell efflux of K⁺ include exercise, extracellular fluid hyperosmolality, cell breakdown, and acidosis

Question 32

Most of the excreted K⁺ is excreted in ______, while most K⁺ that remains is found in the ______

Answer 32

Most of the excreted K⁺ is excreted in urine, while most K⁺ that remains is found in the muscles

Question 33

Principal cells of the cortical collecting duct are the primary site of _______

Answer 33

Principal cells of the cortical collecting duct are the primary site of K⁺ secretion

(high K⁺ inside cell and unpaired negative charge left behind in lumen when Na⁺ is reabsorbed are driving forces for K⁺ secretion)

(anything that affects Na⁺ reabsorption affects K⁺ secretion)

Question 34

_______ and _______ are driving forces for K+​ secretion

Answer 34

High K+ inside cell and unpaired negative charge left behind in lumen when Na+ is absorbed are driving forces for K+​ secretion

Question 35

Principal cells of the cortical collecting duct are the primary site of action of ______

Answer 35

Principal cells of the cortical collecting duct are the primary site of action of K⁺ sparing diuretics

(amiloride)

Question 36

Describe factors promoting K⁺ secretion

Answer 36

Factors promoting K⁺​ secretion

• Increased Na⁺ reabsorption
• Aldosterone
• Other mineralocorticoids
• High tubular fluid flow
• Bicarbonate in tubular fluid
• Non-reabsorbable ions

Question 37

Describe factors impairing K⁺ secretion

Answer 37

Factors impairing K⁺​ secretion

• Decreased Na⁺ reabsorption
• Aldosterone antagonists
• K⁺ sparing diuretics
• Low tubular fluid flow
• ACE inhibitors