Tubular reabsorption and secretion - Loop of Henle Flashcards
What are the parts of the loop of Henle?
Thin descending limb
Thin ascending limb
Thick ascending limb
What is reabsorbed in the thin descending limb?
Water
How is water reabsorbed in the thin descending limb?
Aquaporin1 channel on apical domain of epithelial cell
Water passes through it from the tubular lumen into the cell
Aquaporin1 channel on basolateral domain of epithelial cell
Water passes through it from the cell into the interstitial fluid
Also moves through paracellular route but less
How does the osmolality change across the length of the thin descending limb? Why?
Increases
ions and molecules become more concentrated in tubular lumen
as water is reabsorbed without them
What is reabsorbed in the thin ascending limb?
Sodium ions
How are sodium ions reabsorbed in the thin ascending limb?
Move through paracellular route from tubular lumen into interstitial fluid down its concentration gradient, so by passive diffusion
What causes the concentration gradient of sodium ions in the thin ascending limb?
High concentration of sodium ions in tubular lumen from thin descending limb
What is the main primary active transporter in the thick ascending limb?
Na+ K+ ATPase
Where is the Na+ K+ ATPase located on the epithelial cell in the thick ascending limb?
Basolateral domain
What does the Na+ K+ ATPase in the thick ascending limb 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 thick ascending limb?
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 thick ascending limb?
It is used in reabsorption of other substances by secondary active transport
What is reabsorbed in the thick ascending limb?
Sodium ions
Potassium ions
Chloride ions
Calcium ions
Magnesium ions
How are potassium and chloride ions reabsorbed in the thick ascending limb?
NKCC2 transporter on apical domain of epithelial cell
Moves one sodium ion, one potassium ion and two chloride ions from the tubular lumen into the epithelial cell
Potassium ion is moving against its concentration gradient, but the sodium and chloride ions are moving down their concentration gradient, so is secondary active transport
CIC-KB channel on basolateral domain of epithelial cell
Chloride ions move through it from the cell into the interstitial fluid down their concentration gradient, so by facilitated diffusion
What happens to the potassium ions in the epithelial cell in the thick ascending limb?
ROMK channel on apical domain of epithelial cell
Potassium ions move through it from the epithelial cell back into the tubular lumen down their concentration gradient, so by facilitated diffusion