Positive/Negative Feedback loop

1
Positive/Negative Feedback loop

• Important Point Secretions are pulsatile vs.
  continuous

2
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
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
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
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
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