Physiology - Renal Topic #5

  1. Hormonal control
    • ADH / vasopressin control of water permeability
    • major role: determines ECF osmolarity
    • enin angiotensin aldosterone (RAA) System - regulates ECF volume (Na reabsorption)
  2. 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?
    • 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
    • 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
  5. 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
  6. Disturbances in Salt/Water Balance in the ECF
  7. 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
  8. 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
  9. 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
Card Set
Physiology - Renal Topic #5
Topic #5 - Control of Fluid Balance