2/15 Disorders of Puberty - Radovick Flashcards
endocrine system graphic
female HPG axis
hypothal_GnRH neurons : GnRH
ant pituitary_gonadotropes : FSH & LH
ovaries : P4 (progesterone) & E2 (estradiol)
→→→ endometrium, female phenotype
feedback
- estradiol has two types of feedback
- positive feedback at level of GnRH neuron (hypothal) and pituitary → midcycle surge of LH → ovulation
- negative feedback: high levels of E2 decr levels of GnRH, FSH, LH
male HPG axis
hypothal_GnRH neurons : GnRH
ant pituitary_gonadotropes : FSH & LH
testes : T (testosterone)
→→→ male phenotype, spermatogenesis
feedback
- only one type of feedback
- negative feedback: high levels of T decr levels of GnRH, FSH, LH
GnRH
gonadotropin releasing hormone
decapeptide synth’d via cleavage from pre-pro-GnRH protein in preoptic nuclei
GnRH secretion is PULSATILE
migration of GnRH neurons
disease of non-migration
GnRH neurons and olfactory neurons move from olfactory placode through cribriform plate to anterior hypothalamus
**MIGRATION IS CRITICAL
- no migration? disease
Kallmann Syndrome: hypothalamic hypogonadism (assoc with anosmia)
- KAL1 protein directs migration (adhesion protein)
- if mutated? GnRH deficiency → anosmia, hypogonadism
GnRH receptor signaling
GnRH hits GnRH receptor in ant pit → FSH, LH synthesis and secretion via stimulation of subunit genes
ALSO stimulates subunit genes
desensitization of GnRH has effects on pulsatility of LH (more) and FSH (some)
- lack of cytoplasmic tail → reduced receptor desensitization and internalization
pituitary and placental glycoprotein family
- LH
- FSH
- TSH
- hCG
- common alpha subunit + hormone-specific beta subunit
- glycosylation essential for fx
pulsatility of GnRH
pulsatility of GnRH → pulstility of LH/FSH secretion
continuous infusion?
no pulsatility of LH/FSH
implication: if you have too much FSH/LH (ex. precocious puberty) and you need to tone it down → cont infusion GnRH is an option → hypogonadism
two cell hypothesis of ovary
-
theca cell: LH receptors
- LH receptors are Gprotein-coupled → Gs → make adenylyl cyclase → incr cAMP
- make androstenedione
-
granulosa cell: FSH receptors
- FSH receptors are also Gprotein-coupled → make adenylyl cyclase → incr cAMP → conversion of androstenedione from theca cells into E2 (estradiol)
testes
-
Leydig cell: LH receptors
- make testosterone
-
Sertoli cell: FSH receptors
- concentrates testosterone from Leydig cells → req for spermatogenesis
kisspeptin
pubertal trigger
- upstream of GnRH
- important in triggering puberty and ovulatory surge of gonadotropins
HPG axis summary
puberty
definition
puberty: hormones & processes
adrenarche: hormones & processes
period of life during which acquisition of secondary sexual characteristics occurs
puberty
hypothal:GnRH → pituitary:FSH/LH → testes/ovaries:testosterone/estradiol
GONADARCHE: incr size of testes (due to testosterone incr)
THELARCHE: onset of breast devpt
adrenarche
pituitary:ACTH → adrenal:DHEA/DHEAS → adrenal androgens
TANNER2-3: PUBIC HAIR
Tanner stage
breasts
stage1 : no breast tissue
stage2 : breast bud; elevation under areola (onset ~10y)
stage3: enlargement of breast tissue beyond areola, no separation of contours
stage4 : projection of areola and papilla to form secondary mound above level of breast
stage5 : mature stage
Tanner stage
pubic hair
stage1 : no pubic hair
stage2 : sparge growth of long, pigmented hair on labia
stage3 : darker, coarser, curlier hair on pubis
stage4 : adult-type hair, but less quantity
stage5 : adult0type and quantity, inverted triangle