endocrine and metabolic disorders
Overview of the Endocrine System
Posterior Pituitary Function
The posterior pituitary releasesvasopressin(also calledargininevasopressinor antidiuretic hormone [ADH]) andoxytocin. Both hormones are released in response to neural impulses and have half-lives of about 10 minutes. Vasopressinacts primarily to promote water conservation by the kidneys by increasing the permeability of the distal tubular epithelium to water. At high concentrations,vasopressinalso causes vasoconstriction. Likealdosterone,vasopressinplays an important role in maintaining fluid homeostasis and vascular and cellular hydration. The main stimulus forvasopressinrelease is increased osmotic pressure of water in the body, which is sensed by osmoreceptors in the hypothalamus. The other major stimulus is Volume Depletion , which is sensed by baroreceptors in the left atrium, pulmonary veins, carotid sinus, and aortic arch, and then transmitted to the central nervous system through the vagus and glossopharyngeal nerves. Other stimulants for causes ArginineVasopressin Deficiency (Central Diabetes Insipidus) . An inability of the kidneys to respond normally to in the posterior pituitary. Measuring it may be useful in distinguishing the cause of Hyponatremia . Oxytocinhas 2 major targets: Myoepithelial cells of the breast, which surround the alveoli of the mammary gland Smooth muscle cells of the uterus Suckling stimulates the production ofoxytocin, which causes the myoepithelial cells to contract. This contraction causes milk to move from the alveoli to large sinuses for ejection (ie, the milk letdown reflex of nursing mothers).Oxytocinstimulates contraction of uterine smooth muscle cells, and uterine sensitivity tooxytocinincreases throughout pregnancy. However, plasma levels do not increase sharply during parturition, and the role ofoxytocinin the initiation of labor is unclear. There is no recognized stimulus foroxytocinrelease in men, although men have extremely low levels. 