L106: Kidney 2 Flashcards
Where does reabsorption occur?
Renal tubule
What does the renal tubule comprise of?
- PCT;
- LoH;
- DCT;
- Collecting duct.
What part of the kidney are the PCT and DCT located?
Cortex
What part of the kidney are the LoH located?
Medulla
What is the primary location for reabsorption?
PCT (~65%)
How is reabsorption in the PCT facilitated?
Sodium active transport (primary active transport), everything follows sodium (aka sodium handling)
What process occurs at the LoH?
Countercurrent multiplication
What is the main function of countercurrent multiplication?
Water reabsorption, concentration of urine
What part of the nephron is responsible for fine-tuning of the filtrate?
DCT
What three hormones modulate water reabsorption in the DCT?
- Anti-diuretic hormone;
- Aldosterone;
- Atrial-natriuretic hormone.
What direction do water and nutrients move when reabsorbed?
From tubule to blood
What direction do water and nutrients move when secreted?
From blood into tubule (form urine)
What structural specialisation facilitates maximal reabsorption in the PCT?
- Microvilli;
- Convoluted (winding);
- Closely located to peritubular capillaries.
How are water and nutrients reabsorbed in the PCT?
Passive diffusion (and secondary active transport to sodium) (50%)
Why do nutrients diffuse from the tubule lumen to the peritubular capillaries? (in PCT)
Higher concentration in lumen than blood, therefore they move down a concentration gradient
What do nutrients/ molecules require to passively diffuse into the capillaries in the PCT?
- Pores/ carrier proteins to cross phospholipid bilayer;
- Water: aquaporins;
- No ATP.
What molecules are co-transported via sodium? (PCT)
Glucose and amino acids (passive but facilitated)
What ion exchange occurs on the basolateral membrane during sodium reabsorption? (PCT)
3 x Na+ OUT, 2 x K+ IN
What direction does sodium move during active transport?
Against a concentration gradient
What process results in water being reabsorbed as a result of sodium active transport? (PCT)
Osmosis
What process results in Cl- and other -ve ions being reabsorbed as a result of sodium active transport? (PCT)
Electrical gradient
How much sodium reabsorption occurs in the LoH?
~25%
What type of nephrons are specialised for countercurrent multiplication and why?
Juxtamedullary, due to long LoH
How is the LoH specialised to facilitate countercurrent multiplication?
- Thin descending limb: permeable to water and no sodium reabsorption;
- Thick ascending limb: impermeable to water (no aquaporins), active sodium reabsorption.
