Tubular processing Flashcards
Which 4 substances have reabsorption rates close to 100%?
Glucose
Bicarbonate
Sodium
Chloride
The sodium-potassium ATPase pump in the nephrons exchanges how many sodium ions for how many potassium ions?
3 sodium ions for 2 potassium ions
How and in what way does the sodium-potassium ATPase pump on the basolateral membrane of nephron cells affect the intracellular voltage?
Creates a negative intracellular voltage
Because 3 sodium ions are exchanged for only 2 potassium ions
The majority of reabsorption occurs in which part of the nephron?
PCT
Describe the osmolarity of the fluid leaving the PCT compared to interstitial fluid.
Isosmotic with the interstitial fluid
Which ions are secreted in the PCT?
Hydrogen ions (H+)
By what mechanism is glucose reabsorbed in the PCT?
SGLT2 (secondary active transport)
By what mechanism are amino acids reabsorbed in the PCT?
Coupled with Na+ (secondary active transport)
Why do untreated diabetics experience polyuria?
Glucose in the lumen (which cannot be absorbed due to the SGLT2 transporters reaching the transport maximum), holds water in the lumen via osmosis
By what mechanism are H+ ions secreted in the PCT?
Na+/H+ exchanger (NHE) (antiporter)
In which part of the nephron is there reabsorption of approximately 25% of filtered sodium?
Thick ascending limb
In which part of the nephron does the filtrate become hypoosmotic?
Why is this?
Thick ascending limb of loop of Henle
Because there is active reabsorption of sodium (25% of filtered load), but the thick ascending limb is impermeable to water, so water remains in the lumen
By which mechanism is sodium reabsorbed in the thick ascending limb?
NKCC2 co-transporter
By which mechanism is chloride reabsorbed in the thick ascending limb?
NKCC2 co-transporter
By which mechanism is potassium reabsorbed in the thick ascending limb?
NKCC2 co-transporter
What is the charge of the lumen in the thick ascending limb?
What creates this charge?
Slightly positive
Potassium, after being brought into the cell via the NKCC2 transporter against its concentration gradient, leaks back out into the lumen, creating a slightly positive charge
Describe how calcium and magnesium are absorbed in the thick ascending limb.
A slightly positive charge in the lumen, caused by the leakage of potassium, encourages calcium and magnesium to diffuse in a paracellular route between cells
In which part of the nephron does the sodium-chloride co-transporter first appear?
Early distal tubule
Describe the water permeability of the late distal tubule and cortical collecting duct.
Under hormonal control by ADH
When ADH is present, is the late distal tubule and cortical collecting tubule permeable or impermeable to water?
Permeable to water
When ADH is absent, is the late distal tubule and cortical collecting tubule permeable or impermeable to water?
Impermeable to water
What are the 2 main cell types of the late distal tubule and cortical collecting tubule?
Principal cells
Intercalated cells
What is the function of principal cells in the late distal tubule?
Sodium reabsorption and potassium secretion
Which key transporter is found on the luminal membrane of principal cells of the late distal tubule?
ENaC (epithelium sodium channels)
