T3 hypothalamus-pituitary axis

anterior pituitary - connection type

neuroendocrine → endocrine

posterior pituitary - connection type

neuroendocrine

anterior pituitary - hypothalamus produce

releasing / inhibiting hormones

hypophyseal portal system

pathway from of hormones from hypothalamus to anterior pituitary

anterior pituitary - respond by

producing and releasing tropic hormones

posterior pituitary - nuclei

paraventricular & supraoptic

paraventricular nuclei

synthesize oxytocin

supraoptic nuclei

synthesize ADH

posterior pituitary - hormones stored at

nerve terminals

posterior pituitary - hormones released when

neuronal stimulation

negative feedback

hormones from target organs inhibit both hypothalamus & pituitary to prevent overproduction

negative feedback - exception

prolactin

prolactin - regulation

inhibition from dopamine

hypothalamic inhibition lost - what increase

prolactin

hypothalamic inhibition lost - what decrease

ACTH, TSH, LH, FSH, growth hormone

hypothalamo-pituitary axis - plasticity

adaptable → can reorganize to meet changing physiological needs

ADH - function

increase water reabsorption & cause vasoconstriction to maintain blood pressure

ADH - secrete in response to

loss of free water & decrease effective circulating volume

oxytocin - released during

nipple stimulation & cervical stretching

oxytocin - nipple stimulation

promote milk ejection via myoepithelial cell contraction

oxytocin - cervical stretching

stimulate uterine contraction

late pregnancy - avoid what

nipple stimulation due to risk of premature uterine contraction

infancy to early childhood - hormones

thyroid hormones → brain development, metabolism, physical growth

childhood and puberty - hormones

growth hormone → stimulate liver to produce IGF-1 → promote linear growth

puberty onset - hormones

estrogen & testosterone → puberty growth spurt, GH secretion, epiphyseal plate closure

regulation of growth hormone secretion

growth hormone-releasing hormone (GHRH) & somatostatin

GHRH - released from

hypothalamus

GHRH - function

stimulate somatotrophs to produce and secrete GH

somatostatin - released from

hypothalamus

somatostatin - function

inhibit somatotrophs → suppress GH

IGF-1 inhibits what

GH from pituitary & GHRH from hypothalamus

IGF-1 stimulate what

somatostatin → further inhibit GH

growth hormone - indirect effects

stimulate cartilage formation & bone growth, promote protein synthesis, cell growth, tissue repair

growth hormone - direct effects

fat metabolism, carbohydrate metabolism

factors stimulating GH secretion

decreased blood glucose, decrease free fatty acids, fasting, starvation, stress, trauma, strenous exercise, deep sleep

factors inhibiting GH secretion

increase blood glucose, increase free fatty acids, aging, obesity, somatostatin, exogenous growth hormone, IGF-1

excessive GH secretion disorders

gigantism (children) & acromegaly (adults)

gigantism - occurs when

before epiphyseal plates close

gigantism - leads to

abnormally tall stature

acromegaly - occurs when

after epiphyseal plates closeac

acromegaly - leads to

enlargement of hands, feet, jaw, internal organs

GH deficiency - leads to

short stature, delayed growth, normal body proportions, premature epiphyseal closure

prolactin - function

stimulate mammary gland development & milk production

prolactin - inhibited by

dopamine & progesterone

prolactin - stimulated by

thyrotropin-releasing hormone (TRH), estrogen, breastfeeding/suckling

effects of hyperprolactinemia in women

amenorrhea, galactorrhea, infertility to inhibition of GnRH

effects of hyperprolactinemia in men

decreased libido, erectile dysfunction, gynecomastia