Transport Mechanisms Flashcards
Paracellular (reabsorption)
One step process substance moves in between tubule cells to the capillary
Transcellular (reabsorption)
Two step process, substance moves through luminal membrane then through basolateral membrane an then to the capillary
Aquaporin
specialized water channel used to move water across membrane
Aquaporin I
Found in membranes of vasa recta and luminal membranes of proximal tubule and descending limb
Aquaporin II
hormonally regulated by ADH, found in luminal membrane of collecting duct
Aquaporin III and IV
found in basolateral membrane of collecting duct
Uniporter
permits movement of single type of molecule through membrane. Binding of molecule to itself in order to pass through, molecules pass through this type transporter by facilitated diffusion.
Example: GLUT uniporter which moves glucose from cytosol of tubule across basolateral membrane to interstitium
Symporters
Permits movement of two molecules in same direction across membrane, also called co transport. Some symporters don’t use ATP (energy) and use concentration gradient which is called secondary active transport
Example: Na+/Glucose symporter- important for reabsorption of glucose and sodium from filtrate into tubule epithelial cells
Antiporters
Permits movement of two molecules in opposite directions across a membrane
Example: Na+/H+ anitporter important for exporting protons out of tubule cell in exchange for Na+ entering the cell, also driven by Na+ gradient.
Primary Active Transporters
require ATP to move molecules against their concentration gradient
Example:
Who: Na+/K+ ATPase also known as the Na+/K+ pump
Where: basolateral membrane of tubule epithelial cells
Why: important to keep sodium gradient for other transporters to function
How: Moves 3 sodium ions out of cell into interstitium and 2 potassium cells into cell
What: requires energy because both the movement of Na+ and K+ is against their concentration gradients.
