20 Regulation of Water Balance
Water Reabsorption
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Regulated Permeability in the Collecting Duct
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Regulation of Vasopressin Secretion
Vasopressin
Vasopressin is a peptide hormone that is produced by neurosecretory cells, a type of endocrine cell found in the hypothalamus. As shown in the figure, neurosecretory cells have dendrites, axons, and terminals just like typical neurons. The difference is that the terminals of neurosecretory cells are adjacent to capillaries. Neurosecretory cells secrete regulatory molecules (green dots) that enter the circulation and act as hormones.
neurosecretory cell figure
Vasopressin is from the posterior pituitary. The pituitary gland sits below the hypothalamus and consists of two parts.
Silverthorn 7.8a to show hypothalamus and pituitary
The anterior pituitary (or adenohypophysis) is the glandular part of the pituitary and contains endocrine cells releasing a variety of hormones that control growth, reproduction, lactation, thyroid function, and adrenal function. The posterior pituitary (or neurohypophysis) is effectively an extension of the hypothalamus and contains the axons and terminals of large neurosecretory cells whose cell bodies are found in the hypothalamus.
Silverthorn 20.6a (right)
The figure below details all the ways that vasopressin secretion can be triggered.
Silverthorn 20.6a (left)
The main control of vasopressin secretion is by the osmoreceptors, neurons that sense changes in the osmolarity of the extracellular fluid. The osmoreceptors are also located in the hypothalamus.
AVP-D and AVP-R are Disorders in the Ability to Concentrate Urine
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