Renal III: Tubular Reabsorption and Secretion Flashcards
What is tubular reabsorption?
Materials transfer from tubular fluid back into the blood
Where does most reabsorption occur?
in PCT (rest of nephron does fine tuning)
What is tubular secretion?
When materials are transferred from blood to tubular fluid
How does tubular reabsorption work?
By active and passive processes
Water follows solutes by osmosis
Small proteins move into the blood by pinocytosis
What is paracellular reabsorption?
Reabsorption between cells
50% of reabsorbed material moves between cells by diffusion
What is transcellular reabsorption?
Reabsorption through cells
Material moves through both apical and basal membranes of tubule cell by active transport
How is water reabsorbed?
Only by osmosis
What is obligatory water reabsorption?
Water is “obliged” to follow the solutes being reabsorbed
Reabsorption always happens
What is facultative water reabsorption?
Water reabsorption is under control of antidiuretic hormone (ADH)
What do Na+ symporters do?
Help reabsorb materials from tubular filtrate
(Glucose, amino acids, lactic acid, water-soluble vitamins)
What does reabsorption in the PCT rely on?
low intracellular Na+
How are intracellular sodium levels kept low in the PCT?
by Na+/K+ pumps on basolateral side
Is filtrate hypo, iso, or hypertonic to blood at the end of the PCT?
isotonic
What do Na+ antiporters help secrete in the PCT?
acid, H+
What do Na+ antiporters rely on for secretion in the PCT?
low intracellular Na+
What happens when renal threshold is exceeded?
transport is limited
What is a renal threshold?
The limits on rate of transport for renal symporters
What reabsorption occurs in the descending limb of the loop of Henle? And is it active or passive?
osmosis (water reabsorption)
passive reabsorption
What is reabsorbed in the thin ascending limb of the loop of henle? And is it passive or active?
NaCl
passive reabsorption
What symporters does the thick ascending limb of the loop of henle have?
Na+/K+/2Cl-
Is filtrate hypo, iso, or hypertonic at the end of the loop of henle?
hypotonic
Is filtrate hypo iso, or hypertonic in the early DCT?
hypotonic
The early DCT reabsorbs both ions and water, which i s it more permeable to?
water
Is all water reabsorption obligatory or facultative until the late DCT?
obligatory reabsorption
What two cell types are in the late DCT and collecting duct?
Principal cells and intercalated cells
What is the function of principal cells in the late DCT and CD?
reabsorb Na+
reabsorb H2O if ADH is present
secrete K+
What is the function of intercalated cells in the late DCT and CD?
reabsorb K+ and HCO3-
secrete H+
How does drinking water produce dilute urine?
Decreases blood osmolarity
Inhibits ADH release
increases H2O loss in urine
more water in urine = more dilute
Does filtrate osmolarity increase or decrease as it moves down the descending limb of the loop of henle?
increase (more solutes than water)
Does filtrate osmolarity increase or decrease as it moves up the ascending limb of the loop of henle?
decreases (solutes leave)
Does filtrate osmolarity increase or decrease in the collecting duct?
decreases to produce dilute urine
Does ADH make the late DCT and CD permeable or impermeable to water?
permeable, allows for maximum water reabsorption
(anti-diuretic, less urine = want less water in urine)
