Tubular reabsorption and secretion - DCT Flashcards
What are the parts of the distal convoluted tubule?
DCT1
DCT2
What is the main primary active transporter in the DCT1?
Na+ K+ ATPase
Where is the Na+ K+ ATPase located on the epithelial cell in the DCT1?
Basolateral domain
What does the Na+ K+ ATPase in the DCT1 do?
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
What is the electrochemical gradient of sodium ions in the DCT1?
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
What is the importance of the electrochemical gradient of sodium ions in the DCT1?
It is used in reabsorption of other substances by secondary active transport
What is reabsorbed in the DCT1?
Sodium ions
Chloride ions
Calcium ions
How are chloride ions reabsorbed in the DCT1?
NCC transporter on apical domain of epithelial cell
Transports one sodium ion and one chloride ion from the tubular lumen into the cell, both down their concentration gradient
CIC-KB on basolateral domain of epithelial cell
Chloride ions move through from the cell into the interstitial fluid down their concentration gradient, so by facilitated diffusion
What is the difference between the DCT1 and DCT2?
DCT2 has ENaC on the apical domain of its epithelial cells
Method of chloride ion reabsorption
What does ENaC on the apical domain of epithelial cells in the DCT2 do?
Sodium ions move through it from the tubular lumen into the epithelial cell down its concentration gradient, so by facilitated diffusion
How are chloride ions reabsorbed in the DCT2?
Same as in DCT1
But also, sodium ion reabsorption through ENaC makes tubular lumen more negatively charged
Chloride ions move through paracellular route from the tubular lumen into the interstitial fluid down their electrical gradient, so by passive diffusion
How are calcium ions reabsorbed in the DCT?
NCX on basolateral domain of epithelial cell
Moves sodium ion from interstitial fluid into the cell down its concentration gradient whilst moving calcium ion from cell into interstitial fluid against its concentration gradient, so is secondary active transport
Calcium ion uniporter on apical domain of epithelial cell
Calcium ion moves through it from tubular lumen into epithelial cell down its concentration gradient, so by facilitated diffusion
In the cell, calcium ions bind to calbindin which moves towards the basolateral domain of the cell
What controls the reabsorption of calcium ions in the DCT?
Parathyroid hormone (PTH)
1,25-hydroxyvitamin D
How much of the filtered sodium is reabsorbed in the DCT?
5%
How does the osmolality change across the length of the DCT? Why?
Decreases
ions become less concentrated in tubular lumen
because are reabsorbing them without reabsorbing water
