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Control of ECF & Composition III

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BIOL 1840U
Peter Cheung

Control of ECF & Composition III Sodium Balance I. Regulation of ECF volume & composition a. Glomerular-tubular balance—small changes in GFR won’t have large effects on Na excretion b/c renal tubules compensate for changes in GFR by proportional changes in Na reabsorption b. Physical Factors—changes in concentration of solutes (osmolarity) or volume, may be monitored by sensors i. Hydrostatic pressure differences—↑volume => ↑GFR (more “push”) ii. Oncotic pressure differences—as [H2O] ↓, [proteins] ↑ => ↑reabsorption c. Hormonal Factors—released in response to GFR change or diff. rates of substance reabsorption Segment Hormone Effect Proximal Tubule Angiotensin ↑ NaCl reabsorption (vasoconstriction) TAL/ DCT / CCT Aldosterone ↑ NaCl reabsorption Distal/Collecting Atrial Natriuretic ↓ NaCl reabsorption (↑GFR => Duct Factor (ANF) ↑excretion) i. Renin-Angiotensin System 1. ↓BP => macula densa cells signal J-G cells →release renin → converts angiotensinogen to angiotensin I →at lungs, angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II →↑BP in several ways: 1) stimulates ADH release, 2) stimulates aldosterone release, 3) promotes vasoconstriction 2. Aldosterone— a. Synthesized/released in zona glomerulosa cells of adrenal cortex b. Fxn: ↑NaCl reabsorption in DCT/ Collecting ducts by ↑ transcription of proteins that ↑ Na channel activity c. Regulation: ↑[Na]plasma => ↓ aldosterone secretion i. ↑[K] & ↑[ACTH] =
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