Water balance

Normally maintained by the Hypothalamus-Neurohypophyseal-Renal axis.

The above system maintains water balance during water intake variations and non-renal losses of water.

As the body’s universal solvent and as a means of removing excess heat, water is vital for survival.

Water balance regulation utilizes a feedback mechanism involving the hypothalamus, the neurohypophysis, and the kidneys.

Water homeostasis depends on receptors residing along the anterior wall of the brains third ventricle that responds to serum tonicity and angiotensin II by regulating water intake (thirst) and water excretion (release of ADH).

Recommended intake volumes in the elderly are the same as for younger adults (2.0 L/day for females and 2.5 L/day for males).

Water moves freely across membranes, and the concentration of water relative to dissolved osmoles is a critical parameter.

Osmoreceptors in the hypothalamus sense plasma osmolality and in part are dependent on activation of nonselective calcium-permeable cation channels in osmosisensing neurons that serve as stretch receptors.

Plasma osmolality physiologic threshold is 290 to 295 mOsm per kilogram of water in most individuals.

When plasma osmolarity increases above the physiologic threshold there is an increased secretion of vasopressin from vasopressinergic nerve endings in the neurohypophysis.

Increased plasma osmolality triggers thirst.

With two little water, sales shrink and with too much, they swell.

The normal blood osmolality is approximately 290 mOsm per kilogram and is tightly defended.

The brain senses perturbations in blood osmolality and secondarily by detecting changes in angiotensin II.

The brain restores balance by adjusting excretion, by changing the activity of vasopressin neurons, which alters vasopressin levels in the blood, and by regulating thirst.

Vasopressin (ADH) is secreted by hypothalamic neurons in response to hypertonicity and decreased effective arterial blood volume.

Three brain nuclei in the laminate terminalis along the anterior wall of the third ventricle play key roles in regulating what a balance.

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