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Hormonal control
- ADH / vasopressin control of water permeability
- major role: determines ECF osmolarity
- enin angiotensin aldosterone (RAA) System - regulates ECF volume (Na reabsorption)
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RAA pathway
- RENIN released from: granular cells of juxtaglomerular apparatus
- stimuli for release: reduced afferent arteriole pressure, lower Na load (reflects ECF volume), and increased sympathetic activity
- Renin: cleaves angiotensinogen (from liver) to form angiotensin 1
- converted in lung and arteries by angiotensin converting enzyme (ACE) in to angio tensin 2
- promotes release of aldosterone from adrenal cortex
what would an ace inhibitor cause?
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ANGIOTENSIN II
- effects: causes arteriolar constriction
- GFR increased: low A2 constricts the efferent arteriole
- GFR decreased: high A2 constricts the afferent arteriole
- stimulates proximal tubule Na reabsorption
- stimulates aldosterone release from adrenal cortex
- promotes thirst
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ALDOSTERONE
- increases Na absorption by distal tubules and collecting ducts (in the principal cells)
- effects: creates new Na channels (ENaC)(apical surface) and Na/K ATPase
- promotes K secretion from distal tubule
- high plasma K levels can trigger aldosterone release directly
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Atrial Natriuretic Hormone (ANH)
- released by: atrial muscle cells
- stimulus for release: atrial stretch from increased ECF volume
- effects: promotes natriuresis (Na excretion)
- promotes Na re absorption from colecting duct
- increases GFR
- dialates afferent arterioles
- increases glomerular permeability
- decreases cardiac out put
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Disturbances in Salt/Water Balance in the ECF
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1. ECF Hypertonicity
- water loss without equal electrolyte loss thus causeing dehydration (not just volume depeltion
- possible causes:
- 1:insufficient water intake
- 2: heavy sweating
- 3:vommiting, osmotic diarrhea
- 4: diabetes insipidus (lacks ADH release from the pituitary so renal tubules cant reabsorb water)
- 5: diabetes mellitus (glucose cant enter cells so plasma levels increase causing glucose to spill into unrine bringing water with it)
- result: water moves out of cells until ICF equalibriates with ECF
- cells srhink
- neuron function in brain is compramised possibly causing a coma
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2. ECF Hypotonicity
- excess water relative to electrolytes=overhydration
- possible causes: rapid water ingestion without electrolytes
- excess ADH release
- result: fluid moves from ECF to ICF
- cells swell
- confusion headaches, vommiting, coma
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3. Isotonic ECF disturbances
- isotonic fluid loss occurs when: equivelant loss of fluid and electrolytes
- example: hemmorage/large volume diarrhea no fluid shift out of cells since no change in osmolarity
- isotonic fluid gain:
- example isotonic saline infusion
- NO osmotic gradient so expansion of ECF only
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