Theme 3 - Part II Flashcards
LOH
- Use
- Thin descending
- Thick ascending
Recover fluid and solute form glomerular filtrate
Thin descending: Flat, no active transport and freely permeable. TJ
Thick ascending: Tubular wall impermeable. Specialised Na+/K+/2Cl- cotransporter
Fluid in LOH [3]
Entering fluid = isotonic
Water reabsorbed OUT & filtrate is hypertonic (1,200 mOsm)
Solute pumped OUT ascending LOH -> hypotonic (150mOsm)
Countercurrent Multiplication [3]
Create large osmotic gradient within medulla
Facilitated by Na+/K+/2Cl-
transport in ascending limb of LOH
Permits passive reabsorption of
water from tubular fluid in
descending LOH
Urea [5]
Freely filtered at glomerulus
Some reabsorption in PT
LOH & distal tubule relatively impermeable
Urea can diffuse out of
collecting duct into medulla
down its concentration
gradient
This adds to the osmolality
of medullary interstitium
LOH reabsorption
Water (DL), Sodium (AL), Potassium (AL), Chloride (AL)
HCO3-, Calcium and Magnesium
LOH secretion
Urea (variable from collecting duct)
Distal tubule [2]
Active transport - absorb/secrete solute
Sodium and chloride ions ACTIVELY reabsorbed from tubular fluid
Na+ and Cl- for K+ exchange
Throughout DT
Exchange throughout DT
Na+ and Cl- for K+ exchange
Na+ and K+ exchange in
Late DT and early collecting duct
Principal cells
Increase aldosterone = Increase DT sodium reabsorption and inhibit juxtaglomerular cells -> renin -> Ang I -> Ang II
Intercalated cells
- alpha [2]
- beta [2]
Alpha:
- Secrete acid via H+/Na+ or H+/K+ by H+/ATPase
- Reabsorb bicarbonate
Beta
- Secrete bicarbonate via Pendrin
- Reabsorb acid
Na+ and H+ exchanged in
DT and early collecting duct
DT and early collecting duct
Na+ and H+ exchanged in
Late DT and early collecting duct
Na+ and K+ exchange
