Structure and function of the renal tubule Flashcards
What occurs at the Bowman’s capsule and glomerulus?
Large amounts of plasma are filtered
What occurs at the renal tubule?
Filtered fluid is converted to urine
Difference between glomerular filtrate and plasma?
Glomerular filtrate has the same composition as plasma except there are no cells and very little protein
When does urine formation begin?
When large amounts of fluid (that is virtually free of protein) is filtered from the glomerular capillaries into the bowman’s capsule
What is glomerular filtrate?
An ultrafiltrate of plasma
What is the rate at which glomerular filtrate is formed?
At 120 ml/min
What is the rate of urine flow?
~ 1ml/min
How does modification of glomerular filtrate occur?
- The filtration process is relatively non-selective
- Modification occurs along the tubule by the process of reabsorption and secretion of water and various solutes via tubular transport
What is the direction of movement when reabsorption is occurring?
When the direction of movement is from the tubular lumen into the peritubular capillary plasma it is called reabsorption
What is the direction of movement when secretion is occurring?
When the movement is in the opposite direction to reabsorption i.e. peritubular plasma into tubular lumen, it is called secretion
Excretion
Clearing unwanted substances by excretion into urine
Reabsorption
Returning wanted substances
What barriers must substances cross to be reabsorbed?
it must first cross:
- the luminal membrane
- diffuse through the cytosol
- across the basolateral membrane & into the blood (transcellular transport).
- Vice versa for secretion
What are two physiological processes involved with reabsorption/secretion?
- Active transfer
2. Passive transfer
Cellular composition of the tubule?
Tubule has a single cell layer wall
Basolateral membrane
Away from the lumen
Luminal/apical membrane
Towards the lumen
Describe the movement of molecules via active transfer/primary active transport
Moving molecules/ions against their concentration gradient (from low to high)
- Operates against electrochemical gradient
What does active transfer/primary active transport require?
Requires energy: driven by ATP
Describe movement of molecules via passive transfer
Passive movement down concentration gradient (from high to low conc)
- requires suitable route
How does passive transfer occur?
Active removal of one component: concentrates other components
Describe movement of molecules via co-transport/secondary active transport
Movement of one substance down its concentration gradient: generates energy
- Allows transport of another substance against its concentration gradient
Why does co-transport/secondary active transport require?
Carrier proteins
What are the two types of co-transport/secondary active transport?
- Symport
2. Anti-port
Symport
Transported species move in the same direction, e.g. Na+-glucose
Antiport
Transported species move in opposite directions e.g. Na+-H+ anti port
What is counter-transport?
When substance to be transported along with Na binds to carrier protein from inside of cell and comes out
