SM_192a: Functions of the Renal Tubule II

Question 1

Cortical nephrons have _____ loops of Henle, while medullary nephrons have _____ loops of Henle

Answer 1

Cortical nephrons have short loops of Henle, while medullary nephrons have longth loops of Henle

Question 2

______ is near the thick ascending limb of the loop of Henle the past the vascular pole

Answer 2

Macula densa is near the thick ascending limb of the loop of Henle the past the vascular pole

Question 3

Describe the difference in histology between the outer stripe of the outer medulla, inner stripe of the outer medulla, and inner medulla

Answer 3

Histology

• Outer stripe of outer medulla: homogeneous in cellular composition
• Inner stripe of outer medulla: see thin walled segments
• Inner medulla: only see collecting ducts with cellular heterogeneity and thin segments

Question 4

Thick ascending limb of loop of Henle is thicker due to presence of more ______

Answer 4

Thick ascending limb of loop of Henle is thicker due to presence of more mitochondria

Question 5

Juxtaglomerular appratus includes _____, _____, and _____

Answer 5

Juxtalgomerular apparatus includes macula densa, extraglomerular mesangial cells, and granular cells in wall of afferent arteriole

Question 6

In apical membrane of thick ascending limb of the loop of Henle, ______ is the main transporter to get Na⁺ into the cell

Answer 6

In apical membrane of thick ascending limb of the loop of Henle, Na⁺/K⁺/Cl^- symporter is the main transporter to get Na⁺​ into the cell

(blocked by furosemide)

Question 7

Describe Na⁺ reabsorption in the thick ascending limb of the loop of Henle

Answer 7

Na⁺ reabsorption in the thick ascending limb of the loop of Henle

• Enters cell from lumen by crossing apical membrane through Na⁺/K⁺/2Cl^- symporter
• Pumped out into interstitium by Na⁺/K⁺ ATPase

Question 8

In thick ascending limb of loop of Henle, ____ leaks back out into lumen from cells and is recycled

Answer 8

In thick ascending limb of loop of Henle, K⁺ leaks back out into lumen from cells and is recycled

Question 9

Thick ascending limb of loop of Henle has no _____ channels so _____ permeability is low

Answer 9

Thick ascending limb of loop of Henle has no H₂O channels so H₂O permeability is low

(asymmetry between descending and ascending loop of Henle is important for countercurrent multiplier)

Question 10

In the thick ascending limb of loop of Henle, ______ can cross into the interstitium do to unpaired negative charge on the interstitial side and K⁺ on the lumen side

Answer 10

In the thick ascending limb of loop of Henle, divalent cations (Ca²⁺, Mg²⁺) can cross into the interstitium do to unpaired negative charge on the interstitial side and K⁺ on the lumen side

(paracellin-1)

Question 11

Ca²⁺ sensing receptor _____ sodium reabsorption

Answer 11

Ca²⁺ sensing receptor dampens sodium reabsorption

(balances calcium reabsorption - if impaired, unrestricted Ca²⁺ reabsorption so familial hypercalcemia w/ hypocalcuria)

Question 12

The purpose of the countercurrent multiplier is to _______

Answer 12

The purpose of the countercurrent multiplier is to create a gradient of osmolality from cortex to medulla which creates a driving force for water to be absorbed in the collecting duct

(hyperosmotic interstitium in inner medulla)

(important for water absorption and concentration of urine)

Question 13

Water permeability is high in the _______ and _______ of the nephron

Answer 13

Water permeability is high in the proximal tubule and descending limb of loop of Henle of the nephron

(in presence of ADH, collecting duct converted to high water permeability)

Question 14

Describe the countercurrent multiplier

Answer 14

Countercurrent multiplier

1. Active transport of NaCl from ascending limb to interstitial space
2. Water moves from descending limb into interstitial space due to osmotic gradient
3. Occurs iteratively until steady state is reached
4. Hyperosmotic interstitium is produced in inner medulla
5. Can extract water from the collecting duct

Question 15

_____ and _____ are main contributers of osmolality in countercurrent multiplication

Answer 15

NaCl and urea are main contributers of osmolality in countercurrent multiplication

Question 16

Role of the peritubular capillaries (vasa recta) in countercurrent multiplication is to ______

Answer 16

Role of the peritubular capillaries (vasa recta) in countercurrent multiplication is to passively uptake solute and release water

(in sick cell, blood cells clog up vasa recta in inner medulla -> microinfarctions -> attenuates number of long loops of Henle that can concentrate urine)

Question 17

Distal convoluted tubule has a _____ wall and many _____

Answer 17

Distal convoluted tubule has a thick wall and many mitochondria

Question 18

Describe reabsorption in the distal convoluted tubule

Answer 18

Reabsorption in the distal convoluted tubule

• Amount of reabsorption lower than preceding portions (lower fraction of reabsorbed NaCl)
• NaCl transporter to transport Na⁺ into cell and Na⁺/K⁺ ATPase to transport Na⁺ into interstitium
• Ca²⁺ exits cells through the Ca²⁺/3Na⁺ antiporter (if stop sodium reabsorption, potentiate calcium entry)
• Water cannot cross apical membrane

(if high calcium, more prone to form kidney stones)

Question 19

_____ target the Na⁺/Cl^- symporter in the apical membrane of the distal convoluted tubule

Answer 19

Thiazides target the Na⁺/Cl^- symporter in the apical membrane of the distal convoluted tubule

Question 20

Describe the functions of the cortical and medullary collecting duct

Answer 20

• Cortical collecting duct: reabsorbs Na⁺, secretes and reabsorbs acid/bicarbonate, reabsorbs water in presence of ADH
• Medullary collecting duct: reabsorbs Na⁺, secretes and reabsorbs acid/bicarbonate, reabsorbs water in presence of ADH, reabsorbs urea

Question 21

_____ collecting duct reabsorbs urea

Answer 21

Medullary collecting duct reabsorbs urea

Question 22

_____ is formed by collecting ducts of adjacent nephrons

Answer 22

Early collecting duct is formed by collecting ducts of adjacent nephrons

Question 23

Cortical collecting duct is comprised of _____ cells and _____ cells

Answer 23

Cortical collecting duct is comprised of principal cells and intercalated cells

• Principal cells: Na⁺ reabsorption (contains Na⁺/K⁺ ATPase pumps in basolateral membrane)
• Intercalated cells: H⁺, bicarbonate secretion, and reabsorption

Question 24

Collecting duct has _____ epithelia

Answer 24

Collecting duct has tight epithelia (high resistance)

(can withstand steep gradients of charge and pH)

Question 25

Principal cells allow reabsorption of ____ and secretion of ____

Answer 25

Principal cells allow reabsorption of Na⁺ and secretion of K⁺

(impermeable to water)

Question 26

_____ blocks Na⁺ in the cortical collecting duct

Answer 26

Amiloride blocks Na⁺​ in the cortical collecting duct

Question 27

Aldosterone binds to the _____ receptor which upregulates the _____ and _____, promoting _____ from the principal cells of the cortical collecting duct

Answer 27

Aldosterone binds to the intracellular mineralocorticoid receptor which upregulates the Na⁺ channel in the apical membrane and Na⁺/K⁺ ATPase in the basolateral membrane, promoting Na⁺ reabsorption from the principal cells of the cortical collecting duct

Question 28

____ mediates aldosterone action in the principal cells of the cortical collecting duct by promoting placement of more ____ channels in the membrane

Answer 28

SGK1 mediates aldosterone action in the principal cells of the cortical collecting duct by promoting placement of more Na⁺ channels in the apical membrane

(phosphorylates NED4-2 -> prevents ubiquitin-mediated degradation of Na⁺ channels -> more Na⁺ channels in apical membrane)

Question 29

_____ receptors increase water permeability in the principal cells of the cortical collecting duct

Answer 29

Vasopressin receptors increase water permeability in the principal cells of the cortical collecting duct

(promote reabsorption of water)

Question 30

Intercalated cells of the cortical collecting duct regulate _____

Answer 30

Intercalated cells of the cortical collecting duct regulate acid-base

Question 31

_____ intercalated cells of the cortical collecting duct secrete acid

Answer 31

Type A intercalated cells of the cortical collecting duct secrete acid

• Vaculoar pump is used forn transepithelial proton secretion
• Carbonic anhydrase eventually generates bicarb

Question 32

______ intercalated cells of the cortical collecting dudct secrete base

Answer 32

Type B intercalated cells of the cortical collecting duct secrete base

Question 33

Describe the important transporters in the inner medullary collecting duct

Answer 33

Inner medullary collecting duct

• ANP receptor on basolateral membrane causes natriuresis (inhibition of Na⁺ reabsorption) by inhibiting cGMP
• Urea transporters allow urea to enter collecting duct cells and then leave to be concentrated in the interstitium
• Vasopressin receptors allow reabsorption of water