Endocrine Day 3- Pregnancy and Male reprod. Flashcards
What happens to corpus luteum at end of menstural cycle in the absence of pregnancy?
CL degenerates and its produciton of progesterone and estraidol falls
What does the placenta produce during the beginning of preganncy?
HCG (human chorionic gonadotropin)
- This “rescues” the CL by acting on LH receptors on CL
- HCG has same beta subunit to LH and will act on LH receptors on CL
- CL will continue to produce progesterone until HCG levels fall at 9-12 weeks

Progesterone ____ pregnancy
maintains
Why does E/P continue to increase after HCG decreases?
- Placenta starts to make own E/P
- placenta makes estriol (major estrogen of pregnancy)
- Progesterone dominant until end of pregnancy
HCG levels are maintained until what week? Why?
- HCG levels maintained until week 9-12
- once placenta starts making own E/P, then HCG starts to fall
- Corpus luteum is then no longer maintained
What is the main estrogen of pregnancy?
Estriol
What is main estrogen of ovaries?
17-beta-estradiol
What is main estrogen of fat tissue?
Estrone
What is HCG?
- Secreted by trophoblast 7-9 days after ovulation
- responsible for maternal recognition of pregnancy
- same structure and function as LH
- Maintains CL
- Promotes estrogen and progesterone secretion from CL (CL is important in first 3 months)
- Stimulates testosterone production by the testes of male fetus
What triggers delivery process?
- Placental CRH stimulates fetal production of ACTH–> DHEA-S produced by fetus–> placenta where aromatase enzyme causes increase in local estrogen/progesterone ratio
- Increase in local prostaglandin (PGF-2 alpha)
- Increase in maternal oxytocin
- increase in maternal catecholamines
What stimulates secretion of labor hormones?
- Stretch receptors in cervix progject infor to anoxal projections in spinal cord
- cause increase in oxytocin from post pituitary
- increases prostaglandins from uterine wall
- causing increase in uterine contractions
oxytocin is major player in uterin contractions
What stimulates synthesis of breast milk?
Prolactin
What stimulates milk ejection?
Oxytocin
What acts on pre-pubertal femals breast to increase duct growth?
- Estrogen
- GH
- Adrenal steroids
What causes mammary gland development during pregnancy?
- Estrogen
- also acting on ant pituitary lactotrophs to increase enlargement/proliferation in preparation for breast feeding
- BUT high estrogen and progesterone block breast milk synthesis
-
Progesterone<– main one
- development of lobule-alveolar system
- prolactin
- GH
- adrenal steroids
What allows milk secretion?
- Once E/P levels diminish after delivery of placenta, then prolactin levels are allowed to increase and breast milk can be made
E and P ____ milk production
inhibit
____ causes growth of ductile system in breasts
____ causes development of lobular-alveolar system
Estrogen; progesterone
What is the funcitonal unit of the milk duct?
Alveoli
____ provides tonic inhibition of output of prolactin
dopamine
T/F, estrogen increases number and size of lactotrophs
true
also makes them more responsive to stimulatory factors
What does suckling of breast cause hormonally?
- Suckling of breast causes inhibition of dopamine from hypothalamus
- inhibiton of dopamine cause increase in prolactin levels to increase milk production
What hormonal effects does increased prolatin levels have?
- Increased PRL causes signal to increase dopamine (negative feedback to decrease further PRL output)
- Signals dopamine neurons to inhibit LHRH secretion
- this lowers LH/FSH/E/P and causes amenorrhea and state of infertility
- GnRH (LHRH) receive dopaminergic input from dopamein
- when dopamine active, inhibits LHRH, gonadotropin, E/P all in arcuate nucleus
What is relative response of prolactin levels initially after birth versus months out?
- Immediately after placenta birthed, prolactin levels allowed to increase and will increase rapidly with suckling episode
- Months later, level of PRL released with suckling decreases
- this allows LHRH neurons to escape dopamine inhibition and fertility is restored