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

Somatotrophs (40-50% in pars distalis) Hypothalamus Pituitary gland Liver GH via Somatotrophs IGF-1 GHRH via Arcuate Nucleus - Somatostatin via PV nucleus (GIH) ALSO by Elevated blood glucose -Also inhibited by melatonin from pineal gland Neural input + 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)

+ Mammotrophs (15-20%) Hypothalamus TRH via dorsomedial Pituitary gland Mammary glands Prolactin TRH via dorsomedial Nucleus; Prolactin RH Prolactin Inhibiting H (dopamine) via Arcuate nucleus Neural input + 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

+ Gonadotrophs (10%) Hypothalamus GnRH via arcuate nucleus Pituitary gland Reproductive Organs FSH/LH Various hormones GnRH via arcuate nucleus Melatonin from the pineal gland inhibits gonadotropin Neural input + 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

+ Thyrotrophs (5%) TSH Hypothalamus Thyrotropin RH via Pituitary gland Thyroid Gland TSH T3(inhibitory) T4 Thyrotropin RH via dorsomedial nucleus Neural input + 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

+ Corticotrophs (20%) Hypothalamus Pituitary gland Adrenal cortex Corticotropin (ACTH) Cortisol Corticotropin RH via paraventricular nucleus (anterior portion) Neural input + ***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