Renal - Physiology (Nephron Physiology, Tubular defects, & Relative concentrations)

Question 1

Which part of the nephron contains a brush border?

Answer 1

Early proximal tubule

Question 2

What substances are fully versus mostly reabsorbed in the early proximal tubule?

Answer 2

Reabsorbs all of the glucose and amino acids and most of the bicarbonate, sodium, chloride, phosphate, and water.

Question 3

What kind of absorption occurs in the early proximal tubule?

Answer 3

Isotonic absorption

Question 4

What role does the early proximal tubule play with regard to ammonia? What function does ammonia have?

Answer 4

Generates and secretes ammonia, which acts as a buffer for secreted H+

Question 5

By what mechanism does PTH act in the proximal tubule? What consequence does this have?

Answer 5

PTH - inhibits Na+/phosphate cotransport –> phosphate excretion

Question 6

By what mechanism does AT II act in the proximal tubule? What consequence does this have? What does this permit?

Answer 6

AT II - stimulates Na+/H+ exchange –> increase Na+, H2O, and HCO3- reabsorption (permitting contraction alkalosis)

Question 7

What percentage of Na+ is reabsorbed in the PCT?

Answer 7

65-80% Na+ reabsorbed

Question 8

What effect does the thin descending loop of Henle have on urine tonicity, and how?

Answer 8

Thin descending loop of Henle - passively reabsorbs H2O via medullary hypertonicity (impermeable to Na+). Concentrating segment. Makes urine hypertonic.

Question 9

What substances does the thick ascending loop of Henle actively reabsorb?

Answer 9

Actively reabsorbs Na+, K+, and Cl-

Question 10

What effect does the thick ascending loop of Henle have on Mg2+ and Ca2+, and via what mechanism?

Answer 10

Indirectly induces the paracellular reabsorption of Mg2+ and Ca2+ through (+) lumen potential generated by K+ backleak

Question 11

What role does the thick ascending loop of Henle play in the handling of water? What consequence does this have?

Answer 11

Impermeable to H2O. Makes urine less concentrated as it ascends.

Question 12

What percentage of Na+ is reabsorbed in the thick ascending loop of Henle?

Answer 12

10-20% Na+ reabsorbed

Question 13

What substances does the early distal convoluted tubule actively reabsorb?

Answer 13

Actively reabsorbs Na+, Cl-

Question 14

What effect does the early distal convoluted tubule have on urine tonicity?

Answer 14

Makes urine hypotonic.

Question 15

By what mechanism does PTH act in the early distal convoluted tubule? What consequence does this have?

Answer 15

PTH - increase Ca2+/Na+ exchange –> Ca2+ reabsorption

Question 16

What percentage of Na+ is reabsorbed in the early distal convoluted tubule?

Answer 16

5-10% Na+ reabsorbed

Question 17

What substance(s) do the collecting tubules reabsorb versus secrete? What regulates this activity?

Answer 17

Reabsorb Na+ in exchange for secreting K+ and H+ (regulated by aldosterone)

Question 18

On what receptor does Aldosterone act? What effect does its action have?

Answer 18

Aldosterone - Acts on mineralocorticoid receptor –> insertion of Na+ channel on luminal side

Question 19

By what mechanism does ADH act? What effect does its action have, and where?

Answer 19

ADH - acts at V2 receptor –> insertion of aquaporin H2O channels on luminal side; Collecting tubule

Question 20

What percentage of Na+ is reabsorbed in the collecting tubules?

Answer 20

3-5% Na+ reabsorbed

Question 21

Draw a schematic of the proximal convoluted tubule, depicting the effects of (1) Angiotensin II and (2) Carbonic anhydrase inhibitors.

Answer 21

See p. 528 in First Aid 2014 or p.483 in First Aid 2013 for visual at top left

Question 22

Draw a schematic of the thick ascending limb of the loop of Henle, depicting (1) the method behind the diffusion of K+ and Cl- down the electrochemical gradient and (2) the effects of Loop diuretics.

Answer 22

See p. 528 in First Aid 2014 or p. 483 in First Aid 2013 for visual at bottom left

Question 23

Draw a schematic of the early distal convoluted tubule, depicting the effects of (1) Thiazide diuretics and (2) PTH.

Answer 23

See p. 528 in First Aid 2014 or p. 483 in First Aid 2013 for visual at top right

Question 24

Draw a schematic of the collecting tubules, depicting the effects of (1) Amiloride, triameterene, (2) Aldosterone, and (3) ADH.

Answer 24

See p. 528 in First Aid 2014 or p. 483 in First Aid 2013 for visual at bottom right

Question 25

Draw the nephron, labeling the following: (1) collecting tubule (2) early distal convoluted tubule (3) early proximal convoluted tubule (4) thick ascending loop of Henle (5) thin descending look of Henle.

Answer 25

See p. 528 in First Aid 2014 or p. 483 in First Aid 2013 for visual in middle & bubbles indicating tubule names

Question 26

What and where is the defect in Fanconi syndrome? What effects does this have?

Answer 26

Reabsorptive defect in PCT. Associated with increased excretion of nearly all amino acids, glucose, HCO3-, and (PO4)3-. May result in metabolic acidosis (proximal renal tubular acidosis).

Question 27

What can cause Fanconi syndrome?

Answer 27

Causes include hereditary defects (e.g., Wilson disease), ischemia, and nephrotoxins/drugs.

Question 28

What are the major renal tubular defects and where does each occur?

Answer 28

Think: “the kidneys put out FABulous Glittering Liquid”; FAnconi syndrome is the 1st defect (PCT), Bartter syndrome is next (thick ascending loop of Henle), Gitelman syndrome is after Bartter (DCT), Liddle syndrome is last (collecting tubule)

Question 29

What and where is the defect in Bartter syndrome? What effects does this have?

Answer 29

Reabsorptive defect in thick ascending loop of Henle. Autosomal recessive, affects Na+/K+/2Cl- cotransporter. Results in hypokalemia and metabolic alkalosis with hypercalciuria.

Question 30

What and where is the defect in Gitelman syndrome? What effects does this have?

Answer 30

Reabsorptive defect of NaCl in DCT. Autosomal recessive. Leads to hypokalemia and metabolic alkalosis, but without hypercalciuria.

Question 31

How does Gitelman syndrome compare to Bartter syndrome in terms of severity and effects?

Answer 31

Less severe than Bartter syndrome. Leads to hypokalemic and metabolic alkalosis (like Bartter), but without hypercalciuria (unilike Bartter)

Question 32

What and where is the defect in Liddle syndrome? What effects does this have?

Answer 32

Increase Na+ reabsorption in distal and collecting tubules (increase activity of epithelial Na+ channel). Autosomal dominant. Results in hypertension, hypokalemia, metabolic alkalosis, decreased aldosterone.

Question 33

What is the treatment for Liddle syndrome?

Answer 33

Treatment: Amiloride

Question 34

What changes occur to tubular inulin concentration along the proximal tubule, and why?

Answer 34

Tubular inulin increase in concentration (but not amount) along the proximal tubule as a result of water reabsorption.

Question 35

How does the reabsorption of Cl- and Na+ compare in the early proximal tubule versus more distally? What consequence does this have?

Answer 35

Cl- reabsorption occurs at a slower rate than Na+ in early proximal tubule and then matches the rate of Na+ reabsorption more distally. Thus, its relative concentration increases before it plateaus.

Question 36

What is TF/P?

Answer 36

TF/P = [Tubular fluid]/[Plasma]

Question 37

When is TF/P > 1?

Answer 37

TF/P > 1 when: Solute is reabsorbed less quickly than water

Question 38

When is TF/P = 1?

Answer 38

TF/P = 1 when: Solute and water are reabsorbed at same rate

Question 39

When is TF/P < 1?

Answer 39

TF/P < 1 when: Solute is reabsorbed more quickly than water.

Question 40

Create a graph with percent distance along proximal tubule on x-axis and TF/P on y-axis. Graph the following substances: (1) Amino Acids (2) Cl- (3) Creatinine (4) Glucose (5) HCO3- (6) Inulin (7) K+ (8) Na+ (9) Osmolarity (10) PAH (11) Pi (12) Urea. Shade in the areas of secretion versus reabsorption on the graph in different colors.

Answer 40

See p. 529 in First Aid 2014 or p. 484 in First Aid 2013 for visual