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Category: Medical

Topic: Fluid Dynamics

Level: Paramedic

Next Unit: ADH and Aldosterone in Fluid Balance

3 minute read

DIURESIS: excretion of water from the kidneys.

ADH: Water balance is achieved mainly by the kidneys through antidiuretic hormone (ADH) that is made by the hypothalamus and then stored by and secreted from the pituitary gland. If diuresis is over-excretion, anti-diuresis is the opposite--that is, prevention of excretion.

ADH causes the re-uptake of water into cells lining the collection ducts of the kidneys. Without ADH, little water is reabsorbed. ADH secretion or inhibition is stimulated by several different receptors:

  • Stimulation: Osmoreceptors located in the hypothalamus are sensitive to increasing plasma osmolarity (when plasma gets too concentrated with solute, as in hypernatremia), causing the release of ADH.
  • Inhibition: Volume-sensitive receptors—stretch receptors—in the atria of the heart are activated by larger than average volumes of blood returning to the heart from the veins and are ADH antagonists—causing decreases in ADH release because the body wants to rid itself of this extra fluid volume.
  • Stimulation vs Inhibition: Baroreceptors in the carotid sinus respond to mean arterial blood pressure and increase or decrease the release of ADH as needed to maintain a certain mean arterial pressure.