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Summers |
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VI. Feedback back to I. Endocrinology of the Reproductive System A. Homeostasis 1. regulation of hormone levels a. control of basal levels b. control of pulsatile release 2. Set Point a. level around which hormone concentrations are regulated B. Negative Feedback 1. e.g. Thermostat 2. Long-Loop Feedback a. gonad is an intermediate b. feed back at locus ceruleus, hypothalamus and pituitary i. ®- = site of feedback 3. Short-loop feedback a. direct feedback by tropic hormones i. LH + FSH inhibit GnRH (at the hypothalamus and brain) 4. Ultrashort Feedback a. releasing hormones and tropic hormones feedback on themselves i. negatively (and positively for GnRH) C. Positive Feedback 1. Females a. Controls LH surge and therefore Ovulation b. Anterior Hypothalamic - Supraoptic - Suprachiasmatic - Center = APS i. regulated by estrogen levels (1) a positive count of how much E2 is in the blood c. Threshold E2 levels trigger APS stimulation of ARC + PON GnRH neurosecretory neurons i. NE + glutamate activate GnRH surge (probably inhibited by endorphins too) (1) GnRH stimulates surge of LH 2. Superultrashort = Paracrine GnRH feedback a. GnRH feedback on ARC GnRH cells plays a role in regulating pulsatile release