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Positive/Negative Feedback loop

+. +. +. Pituitary gland. Neural input. Hypothalamus. Releasing factors. Inhibiting factors. Hormone A. Target organ. Hormone B. Positive/Negative Feedback loop. Important Point: Secretions are pulsatile vs. continuous. +. +. +. Pituitary gland. Neural input. Hypothalamus.

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Positive/Negative Feedback loop

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  1. + + + Pituitary gland Neural input Hypothalamus Releasing factors Inhibiting factors Hormone A Target organ Hormone B Positive/Negative Feedback loop Important Point: Secretions are pulsatile vs. continuous

  2. + + + Pituitary gland Neural input Hypothalamus GHRH via Arcuate Nucleus • - Somatostatin • via PV nucleus • (GIH) • ALSO by • Elevated • blood glucose • -Also inhibited • by melatonin from • pineal gland GH via Somatotrophs Liver IGF-1 Somatotrophs (40-50% in pars distalis) When? Secreted in the morning before waking Effects? IGF-1 binds to chondrocyte receptors on the epiphyseal plates and stimulates long bone/soft tissue growth Defects? Excess (kids) – Gigantism; Deficits (kids) – Dwarfism; Excess (adults) – acromegaly (enlarged hands, feet, jaw, and soft tissues)

  3. + + Pituitary gland Neural input Hypothalamus TRH via dorsomedial Nucleus; Prolactin RH Prolactin Inhibiting H (dopamine) via Arcuate nucleus Prolactin Mammary glands Mammotrophs (15-20%) When? Suckling is the major stimulus of prolactin Effects? To stimulate lactation post partum; Mammary glands stimulate lactation which involves mammogenesis (growth of mammary glands), lactogenesis (stimulating lactation), and galactogenesis (stimulating production of galactose) ***Secretion is regulated by inhibitory factors rather than stimulating factors

  4. + + + Pituitary gland Neural input Hypothalamus GnRH via arcuate nucleus Melatonin from the pineal gland inhibits gonadotropin FSH/LH Reproductive Organs Various hormones Gonadotrophs (10%) Effects?Follicle Stimulating Hormone – folliculogenesis in females (stimulates granulosa cells of ovarian follicle to proliferate and secrete estradiol, activin, and inhibin secretion); stimulates Sertoli cells in seminferous epithelium to synthesize inhibin, activin, and androgen-binding protein Lutenizing Hormone – in females, progesterone secretion by corpus luteum; testosterone by Leydig cells in males Defects? A lack of FSH and LH lead to infertility

  5. + + + Pituitary gland Neural input Hypothalamus Thyrotropin RH via dorsomedial nucleus TSH Thyroid Gland T3(inhibitory) T4 Thyrotrophs (5%) Defects? Hypothyroidism - At the level of the pituitary gland results in low levels of TSH and T3/T4 - At the level of the thyroid gland results in normal levels of TSH and low levels of T3/T4

  6. + + + Pituitary gland Neural input Hypothalamus Corticotropin RH via paraventricular nucleus (anterior portion) Corticotropin (ACTH) Adrenal cortex Cortisol Corticotrophs (20%) ***Also stimulated by stress, low cortisol levels, and vasopressin Effects? Stimulates growth and synthesis of steroid hormones in the adrenal cortex When? In a circadian pattern – high burst in the morning, declining afterwards

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