Tubular reabsorption and secretion - Collecting duct

Question 1

What are the parts of the collecting duct?

Answer 1

Cortical region

Medullary region

Question 2

What are the types of epithelial cells in the cortical collecting duct? Which is more common?

Answer 2

Principal cells - more common

Intercalated cells

Question 3

What is the main primary active transporter in the cortical collecting duct principal cell?

Answer 3

Na+ K+ ATPase

Question 4

Where is the Na+ K+ ATPase located on the epithelial cell in the cortical collecting duct principal cell?

Answer 4

Basolateral domain

Question 5

What does the Na+ K+ ATPase in the cortical collecting duct principal cell do?

Answer 5

Actively transports 3 sodium ions from the epithelial cell into interstitial fluid

Actively transports 2 potassium ions from the interstitial fluid into the epithelial cell

Question 6

What is the electrochemical gradient of sodium ions in the cortical collecting duct principal cell?

Answer 6

High concentration of sodium ions in tubular lumen, positive charge in tubular lumen

Low concentration of sodium ions in epithelial cell, negative charge in epithelial cell

Question 7

What is reabsorbed in the cortical collecting duct principal cells?

Answer 7

Sodium ions

Chloride ions

Water

Question 8

How are sodium ions reabsorbed in the cortical collecting duct principal cells?

Answer 8

ENaC on apical domain of epithelial cell
Sodium ions move through it from the tubular lumen into the epithelial cell down their concentration gradient, so by facilitated diffusion

Question 9

How are chloride ions reabsorbed in the cortical collecting duct principal cells?

Answer 9

Sodium ion reabsorption makes tubular lumen more negatively charged
Chloride ions move through paracellular route from tubular lumen into interstitial fluid down their electrical gradient, so by passive diffusion

Question 10

How is water reabsorbed in the cortical collecting duct principal cells?

Answer 10

Sodium ion reabsorption into epithelial cell then interstitial fluid then peritubular capillaries increases the osmolality of those areas
Draws water in by osmosis

Aquaporin2 channels on apical domain of epithelial cell
Water moves through them from the tubular lumen into the epithelial cell
Aquaporin3 and aquaporin4 channels on basolateral domain of epithelial cell
Water moves through them from the cell into the interstitial fluid

Also moves through paracellular route from tubular lumen into interstitial fluid

Question 11

How much of the filtered sodium ions are reabsorbed in the cortical collecting duct principal cells?

Answer 11

3%

Question 12

What is secreted in the cortical collecting duct principal cells?

Answer 12

Potassium ions

Question 13

How are potassium ions secreted in the cortical collecting duct principal cells?

Answer 13

Sodium ion reabsorption makes the tubular lumen more negatively chargd
ROMK channel on apical domain of epithelial cell
Potassium ions move through it from the cell into the tubular lumen, down their electrical and concentration gradient, so by facilitated diffusion

Question 14

What are the types of intercalated cells?

Answer 14

Alpha-intercalated cells

Beta-intercalated cells

Question 15

What is reabsorbed in the alpha-intercalated cells?

Answer 15

Bicarbonate ions

Potassium ions

Question 16

How are bicarbonate ions reabsorbed in the alpha-intercalated cells in the cortical collecting duct?

Answer 16

AE on basolateral domain of epithelial cell
Moves bicarbonate ion from the epithelial cell into the interstitial fluid, whilst moving chloride ions from the interstitial fluid into the epithelial cell

Question 17

How are potassium ions reabsorbed in the alpha-intercalated cells of the cortical collecting duct?

Answer 17

H+/K+ ATPase on apical domain of epithelial cell
actively transports hydrogen ion from epithelial cell into tubular lumen
whilst actively transporting potassium ion from tubular lumen into epithelial cell

Question 18

What is secreted in the alpha-intercalated cells of the cortical collecting duct?

Answer 18

Hydrogen ions

Question 19

How are hydrogen ions secreted in the alpha-intercalated cells of the cortical collecting duct?

Answer 19

H+/K+ ATPase

H+ ATPase on apical domain of epithelial cell
actively transports one hydrogen ion from the epithelial cell into the tubular lumen

Question 20

What produces the hydrogen ions and bicarbonate ions in the alpha-intercalated cell in the cortical collecting duct?

Answer 20

Carbon dioxide produced by cell metabolism, reacts with water
to produce carbonic acid
which immediately dissociates into hydrogen ion and bicarbonate is.