BIOL 1104 Lecture Notes - Countercurrent Exchange, Nephron, Sodium Chloride

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11 Feb 2013
Conservation of Water—Guggino
I. Intro
a. Daily Excretion: 700ml thru skin, lungs, etc; 900ml thru kidney (urine)
b. Daily Intake: 300ml from metabolism; => NEED 1300ml drinking!
c. Urine entering glomerulus is isotonic (300mOsm/L) w/ plasma
d. Ability of the loop of Henle to concentrate urine is directly related to the length of
the long loops (relative thickness of the medulla)
II. Countercurrent exchange
a. Vasa Recta—capillary system composed of long loops that extend down into the
medulla & ascend (the two vessels are closely adhered); freely permeable to H2O
and solutes
b. As vasa recta descends, it loses H2O and absorbs salt; as it ascends, it gains H2O
and loses salt
c. H2O returns to vasa recta & salts remain in interstitum => body has way to supply
nutrients & O2 w/o upsetting gradient!
III. How does Loop of Henle transport salt & H2O?
* Nephron segments within henle’s loop have different functional characteristics
a. Different passive permeabilities—TDL is permeable to H2O not salt, etc
b. Active transport—thick ascending limb (TALH) is only segment to actively
transport NaCl (via cotransport) => provides driving force
c. Fluid Absorption—Loop absorbs ~25% remaining H2O from urine and put into
vasa recta
IV. How does Loop of Henle generate vertical osmotic gradient? Countercurrent
a. Role of NaCl & H2O
i. Anatomy of renal medulla (counter current flow)
ii. Functional differences w/in nephron => ion gradient
b. Role of Urea
i. Important for countercurrent multiplication
ii. differential permeability to urea =>↑[urea] deep within medulla &
inability to escape afterwards => ↑ concentration in urine
1. DTL, TALH, distal tubules & outer cortical collecting ducts are
impermeable to urea
2. TAL & inner medullary collecting ducts are permeable to urea
c. Summary: different ion permeabilities & active transport of salts permit gradient
formation (Countercurrent multiplication!)
V. How is the Loop of Henle Function Regulated? Antidiuretic Hormone (ADH)
a. Regulates permeability of collecting duct to H2O
b. Also regulates transport of urea out of collecting duct
c. Allows kidney to regulate urine volume at end of process
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