Repro 7 Flashcards
From start of menstrual cycle how many days until implanted blastocyst
20 days
How many cells in blastocyst
~100
2 layers of blastocyst
Trophoblast
Inner cell mass
What does outer cell layer (trophoblast) surround
Inner cell mass
How many days after ovulation does blastocyst implant
~7 days
Upon contact with endometrium what do trophoblasts do
Proliferate and secrete proteolytic enzymes allowing blastocyst to penetrate wall
Outer layer (trophoblast) of blastocyst becomes
Extra embryonic membrane (chorion)
Enclosing embryo and forming placenta
Inner cell mass forms
Embryo and other extra embryonic membranes
Extraembryonic membranes formed by inner cell mass
Amnion
Allantois
Yolk sac
amnion
Secretes amniotic fluid
Allantois
Becomes part of the umbilical cord
How does chorion become placenta
Form chorionic villi that penetrate vascularized endometrium
Secrete enzymes to break down walls of maternal blood vessels
What is exchanged across membrane of villi of placenta
Nutrients, gases and wastes exchanges by diffusion
How big does placenta grow in diameter
~20cm
Hwo much of CO can placenta receive
10%
What does maternal blood bathe in intervillous space
Chorionic villi
Why does embryo secrete hormonal signals
To prevent corpus luteum from degenerating
What does chorionic villi of developing placenta secrete to stimulate corpus luteum
Human chorionic gonadotropin (hCG)
What is hCG similar to
LH
Binds to LH receptors of corpus luteum
What do corpus luteum do when still stimulated
Continue hormone secretion keeping endometrium intact
What does hCG stimulate in male fetuses
Testosterone production in developing testes
What is detected by pregnancy tests
HCG
After 7 weeks what occurs
Placenta takes over hormone production
Corpus luteum not maintained
What hormones does placenta secrete when corpus luteum degenerates and hCG not secreted
Estrogen and progesterone
What hormones does placenta secrete
Progesterone
Estrogen
Human placental lactogen (hPL)
Human placental lactogen AKA
Human chorionic somatomammotrophin
What do estrogen and progesterone from placenta both provide
Negative feedback to HPG axis prevents follicle development
What does estrogen from placenta do
Develop milk secreting ducts in breasts
What does progesterone from placenta do
Maintains endometrium, suppresses uterine contracts (natural smooth muscle relaxant)
What was hPL initially thought to do
Thought to be necessary for breast development during pregnancy and milk production
What does hPL do
Alter mothers glucose and fatty acid metabolism to support fetal growth (decreases insulin sensitivity, increased lipolysis)
- increased circulating glucose so increased uptake to fetus
What does birthing process begin with
Labor
Rhythmic contractions of uterus
What signal initiates contractions
Not completely understood
What are 2 theories for how contractions start
- oxytocin, but usually not increased until after labor
- placenta releasing corticotropin releasing hormone
What happens days prior to onset of labor
Cervix softens and ligaments holding pelvic bones together loosens under enzymatic control (estrogen or relaxin)
At initiation of contractions what occurs
Fetus repositions lower in abdomen putting pressure on stretching cervix initiating positive feedback loop
What drives more forceful contractions
Prostaglandins, oxytocin, CRH, and cervical stretch
Parturition feedback loop
Fetus head pushes downward
Cervix stretch cause uterus contractions adn oxytocin from posterior pituitary
Prostaglandins also act on uterus
What secretes milk
Mammary glands
How many lobes in post pubescent female
15-20 lobes
Each lobe has
Lobules
Each lobule has
Alveoli or acini
Epithelial cells that secrete milk
what stimulates the growth and branching of milk ducts and deposition of fat during puberty
Estrogen
Glands further develop at pregancy due to
Estrogen, growth hormone and cortisol
Final development is caused by
Progesterone converts epithelium into secretory structure
What inhibits milk production
Estrogen and progesterone
Colostrum for initial ~3 days because high estrogen and progesterone for few days
Milk production controlled by
Prolactin secreted from anterior pituitary
Prolactin under control of
Prolactin inhibitory hormone (PIH, dopamine)
Which begins to drop later in pregnancy
What causes milk ejection; let down reflex
Oxytocin by mechanical stimulation or auditory input
Let down reflex
Contraction of smooth muscle in the breast (myoepithelial) and uterus (return to pre pregnancy size)
Path from sucking to milk synthesis
Nipple mechanoreceptor stimulations
Hypothalamus decreases dopamine (PIH)secretion
Anterior pituitary increase prolactin secretion
Increase plasma prolactin
Path from suckling to milk ejection
Nipple mechanoreceptor stimulation
Posterior pituitary increases oxytocin secretion
Increase plasma oxytocin
Contraction of myoepithelial cells
Puberty in females
Budding breasts and first mentsrual
Avg 12 (range 8-13)
Males puberty
Subtle, growth maturation of genitalia, pubic and facial hair, lowering of voice, change in body shape ad height
9-14
Why does puberty occur
Maturation of hypothalamic pituitary pathway
GnRH secreting neurons increase their pulsatile secretion
What causes puberty
Genetically programmed (clock)
Adipose in females (leptin)
Menopause
Cessation of female reproductive cycle
- approx 40 years after first menstrual
- ovaries no longer respond to gonadotropins
What does absence of estrogen cause
Hot flashes, genitalia atrophy, osteoporosis
Andropause
Testosterone production decreases with age
50% of men over 50 have symptoms
Decrease in Leydig cells
