1. 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

2. 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)

3. + 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

4. + 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

5. + 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

6. + 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