Structure and Function fo the renal tubule Flashcards
Where does reabsorption occur?
From the tubular lumen to the peritubular plasma.
Where does secretion occur?
From the peritubular plasma to the tubular lumen
What layers does a reabsorbed molecule have to go through?
It must first cross the luminal membrane – diffuse through the cytosol – across the basolateral membrane and into the blood (transcellular transport). Vice versa for secretion.
What is Active Transfer/Primary Active Transport?
Moving molecule/ion against the concentration gradient (low→high)
Operates against the electrochemical gradient
Requires energy - driven by ATP
What is Passive Transfer?
Passive movement down the concentration gradient (requires suitable route i.e lipid-soluble substances move through lipid matrix and for ions and neutral substances move through water-filled protein channels)
Active removal of one component concentrates other components
What is Co-transport/Secondary Active Transport?
Movement of one substance down its concentration gradient generates energy Allows transport of another substance against its concentration gradient
Requires carrier protein
2 types: symport and anti-port
What is symport?
When transported species move in the same direction
e.g. Na+ and glucose
What is antiport?
When transported species move in opposite directions e.g Na+ H-
What is familial renal glycosuria?
Mutation in the SGLT2 protein gene so glucose just goes straight into the urine.
What are the two types of nephron?
Cortical nephron
85%
Short LoH
They just penetrate the boundary between the inner medulla and outer medulla.
The entire tubular system is surrounded by an extensive network of capillaries
Juxta-medullary nephron
15%
Long LoH
They have long-reach loops that penetrate deep into the medulla (better at concentrating urine).
long efferent arterioles extend from glomeruli to the outer medulla and divided into specialised capillaries (vasa recta) that extend downward into the medulla and lie side by side with loops of Henle
What are the properties of PCT?
High capacity for reabsorption –
special cellular characteristics:
highly metabolic, numerous mitochondria for active transport
extensive brush border on luminal side large surface area for rapid exchange.
A major site of reabsorption. 65-70% of filtered load reabsorbed here.
100% amino acids and glucose. Proteins are degraded into aa and sugar here. and water is also absorbed here.
What is Fanconi’s syndrome?
All PCT reabsorptive mechanisms are defective.
What are the properties of thin descending and ascending Loop of Henle?
Thin epithelial cells, no brush border, few mitochondria and low metabolic activity. Permeable to water.
What are the properties of thick Loop of Henle?
Thick epithelial cells, extensive lateral intercellular folding, few microvilli, many mitochondria so high metabolic activity. Impermeable to water. Lots of active reabsorption of Na.
What are the functions of LOH?
LOH is critical in concentrating/diluting urine. Does this by creating osmotic gradient around the interstitial tissue.
