repro 7 Flashcards
when does the embryo implant in the endometrium?
what is the basic description of a blastocyst?
-approximately 100 cells
-outer cell layer (trophoblast) surrounds an inner cell mass
-implants approximately 7 days after ovulation
-upon contact with endometrium, trophoblasts proliferate and secrete proteolytic enzymes allowing blastocyst to penetrate wall
what does the blastocyst form?
outer layer of blastocyst forms an extra embryonic membrane (chorion), enclosing the embryo and forming the placenta
-inner cell mass forms embryo and other extraembryonic membranes:
-amnion: secretes amniotic fluid (protection)
-allantois: becomes part of the umbilical cord
what is the placenta?
outer layer of cells, chorion, that will become placenta begin to form chorionic villi that penetrate endometrium
-secrete enzymes that break down walls of maternal blood vessels
-nutrients, gases and wastes exchange across membranes of villi mainly by diffusion
-placenta grows to 20cm in diameter and can receive up to 10% of maternal cardiac output
what is hCG?
-corpus luteum has pre programmed 12 day life cycle, the embryo secretes hormonal signals to the prevent corpus luteum from degenerating
-chorionic villi of developing placenta secrete human chorionic gonadotropin (hCG)
-similar to LH, binds to LH receptors of corpus luteum, continues hormone secretion, keeping endometrium intact
-hCG stimulates testosterone production in developing testes in male fetuses
-hCG is hormone detected by pregnancy tests
-after 7 weeks of development (9 weeks of pregnancy) placenta takes over hormone production
what is the table of hormones after pregnancy?
what does the progesterone and estrogen do that is secreted by the placenta?
-negative feedback to HPG axis prevents follicle development
-estrogen: develop milk secreting ducts in breasts
-progesterone: maintains endometrium, suppresses uterine contractions
what are the hormones that the placenta secretes?
-progesterone and estrogen
-human placental lactogen (hPL) aka human chorionic somatomammotropin (hCS)
what does the hPL and hCS do that is secreted by the placenta?
-similar to growth hormone and prolactin, initially thought to be necessary for breast development during pregnancy and milk production
-alters mother’s glucose and fatty acid metabolism to support fetal growth (decreases insulin sensitivity, increased lipolysis)
-in 4% of women, insulin insensitivity leads to gestational diabetes
what is the first part of parturition (the birth process)?
-normally occurs between the 38th-40th week of gestation
-begins with labor, the rhythmic contractions of the uterus
-signals initiating these contractions are not completely understood
-in some animals, a drop in estrogen and progesterone signals contractions, not the case in humans
-signal could be oxytocin, but it doesn’t usually increase until after labor begins (is used to induce labor)
-one theory is that the placenta releases corticotropin-releasing hormone (increased CRH in weeks leading up to birth)
what is the following steps in parturition?
may not know the initiating signal but the sequence of events are understood:
-days prior to onset of labor the cervix softens and ligaments holding pelvic bones together loosens under enzymatic control (estrogen or relaxin)
-at the initiation of contractions, fetus repositions lower in abdomen putting pressure on and stretching cervix initiating a positive feedback loop
what is the positive feedback loop of birth?
what is the anatomy of breasts?
-mammary glands secrete milk during lactation
what are the steps of breasts during and after puberty?
during puberty, estrogen stimulates the growth and branching of milk ducts and deposition of fat
-glands further develop at pregnancy due to estrogen, growth hormone and cortisol
-final development: progesterone converts epithelium into a secretory structure
what is lactation?
-progesterone and estrogen actually inhibit milk production (colostrum initially for 3 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
-oxytocin causes milk ejection “let down reflex”: contraction of smooth muscle in breast (myoepithelial) and uterus
what is the spiderweb of suckling?
