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Physiology (1,062)
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Physiology 3120
Tom Stavraky

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Human Physiology Monday, February 22, 2010 “Endocrine II” Neuroendocrinology • Portal bloodstream travels to anterior pituitary and stimulates release of tropic hormones • Also have long axons that terminate in the posterior pituitary (PP)  Hormones produced in these cells sit there waiting to be released  Vasopressin and oxytocin are stored in PP • 3 types of neurons  Magnocellular (typical)  Hypophysial tropic (majority of neurons)  Axon terminates in portal capillary bed  Hypothalamic projection neuron  Communicates with other neurons; have connective functions • Episodic endocrine secretion  Circadian rhythm (~24 hrs.)  Diurnal rhythm (exactly 24 hrs.); GHRH, CRH, and cortisol follow this rhythm; often used interchangeably with circadian rhythm  Ultradian (not circadian or diurnal; minutes/hours); GnRH, and LH follow this rhythm)  Some hormones have multiple types of patterns depending on context  GH secretion is both diurnal and ultradian (large peak during sleep, but smaller peaks during the day)  Generated in suprachiasmatic nucleus (SCN) of the hypothalamus  Intrinsic circadian pattern of secretion  Regulated expression of “clock” genes (i.e. cryptochromes, and period)  Direct input from retina (non-visual); light resets the pattern (using melatonin from pineal gland)  Light causes signal from SCN to be sent down the spinal cord and then back up to the pineal gland, which then releases melatonin • Major axes regulated by the hypothalamus  HP-adrenal axis (“stress axis”)  Hypothalamus releases CRH (corticotropic releasing hormones); stimulates release of adrenocorticotropic hormone (ACTH) from AP; stimulates adrenal cortex to release cortisol  Cortisol increases blood glucose (via gluconeogenesis, muscle catabolism, inhibit GLUT4 activity); also suppresses immune response  ACTH • Made from POMC (proopiomelanacortin); also a precursor for many other hormones (i.e. MSH, and endorphins)  HP-thyroid axis  Hypothalamus releases TRH and SRIF; stimulate
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