the rest of pregnancy Flashcards
Pregnancy
gestation = time during which development occurs from zygote to infant
- 38 weeks
- embryo: fertilization to 8 weeks
- fetus: 9 weeks to birth
Cleavage
- rapid mitotic divisions without growth
- many small cells to increase surface volume ration
- increases ability to take up nutrients and oxygen and get rid of wastes
- 1st division: blastomeres
- 3 days: morula (16+ cells)
- 4-5 days: blastocyst (100+ cells) –> zona pellucida breaks down (enzymes from endometrium) –> trophoblast cells (outer layer of large flattened cells) –> embryoblast (inner mass of cells) –> blastocoel (fluid filled cavity)
zygote to blastocyst
takes 3-4 days to reach uterus
-steps of implantation are dependent on communication between blastocyst and endometrium
Implantation days 6-7
-prior to implantation blastocyst is nourished by uterine secretions
at 6-7 days:
- trophoblast binds to endometrium
- implants higher vs lower in uterus depending on developmental stage of endometrium
- usually near fundus on posterior wall
- trophoblast releases enzymes and growth factors –> assist in invasion of endometrium
Implantation: days 7-10
-Trophoblasts form 2 layers: inner cytotrophoblast and outer syncytiotrophoblast (protrudes into endometrium)
embryoblast forms 2 layer - embryonic disc
- epiblast = embryo with ectoderm, mesoderm, and endoderm
- hypoblast = extraembryonic structures
- amniotic sac cavity = bt epiblast and amnion –> contains amniotic fluid
blastocoel becomes yolk sac which ultimately degenerates
Final steps of implantation
- uterine cells enclose blastocyst, separating it from uterine cavity
- spaces within syncytiotrophoblast fill with blood from endometrial blood vessel degradation –> eventually fuse together (maternal circulation that nourishes the embryo)
Implantation statistics
- 2/3 of zygotes fail to implant within a week (when endometrium is receptive) OR spontaneously abort (pregnancy lost before 20 weeks)
- 30% of implanted embryos later miscarry due to genetic defects in embryo, uterine malformation (abnormal dvlpmnt of Mullerian ducts), environmental factors, hormone imbalances, etc…
branched (bicornuate) uterus and septate uterus are the most common malformations
Formation of chorionic villus/placenta
-implantation done by day 12
chorionic villi formation
-cytotrophoblast cells protrude through syncytiotrophoblast extensions into endometrium
-embryonic protrusion into these villi –> fetal blood vessels form in the villi
close proximity bt maternal and fetal blood vessels allows for exchange
- proliferation along linig of uterine cavity = placenta
- placental cells don’t have foreign cell markers, so fetal tissue isn’t rejected
Formatino of placenta
Placenta is formed from endometrial and embryonic tissue
- inner: trophoblast and cytotrophoblast formed villi
- Outer: decidual basalis = stratum functionalis of endometrium
Amnion and Amniotic Sac
- cells from epiblast separate and form a space
- outer cells are called the amnion
- fluid w/in space is amniotic fluid –> initailly made by mom, but fetal urine contributes later –> variable amounts during pregnancy (max = 150 ml)
- eventually surround the embryo, providing protection: absorb shock, allow for movement, help maintain constant temp
Umbilical cord
- connects fetus and placenta
- umbilical vein carries blood from mom to fetus (O2 rich blood)
- umbilical arteries carry blood from fetus to mom (waste and O2 poor blood)
Preeclampsia: stats risk factors symptoms causes can lead to...
- 5% of pregnancies
- develops in later stage of pregnancy (>20 weeks)
- leading cause of fetal and maternal death in U.S.
Risks:
- Primiparous and multiparous women >35
- obese and/or hypertensive
- multiple births (e.g. twins)
- fam history
- ethnicity
Symptoms
- hypertension (140/90)
- edema complications (liver damage)
- proteinuria (kidney damage)
Causes = poor dvlpmnt of placental blood vessels –> harder to get maternal blood to fetus
Leads to eclampsia = preeclampsia + seizures –> have to deliver baby right away –> high risk of stroke
Placenta previa
- placenta partially or totally covers cervix
- can cause severe bleeding (hemorrhaging) during delivery
- Symptoms = bright red vaginal bleeding w/o pain during 2nd half of pregnancy
- decrease activities
- C section required
Ectopic pregnancies what? symptoms? treatment? stats?
-Implantation occurs outside uterus: oviduct (tubal) or abdomen (intestines, mesenterie, ovaries)
Symptoms = pain and bleeding –> other structures not able to accomodate growth or maintenance –> stone babies = fetal death + calcification
Surgical removal required
Stats:
- 1% of pregnancies
- causes 10% of maternal deaths
- more common if older, multiparous, nonwhite, have history of pelvic infections/endometriosis, use IUD, or tubal sterilization
Miscarriage
spontaneous abortion
- most happen just before or after implantation w/o being aware of pregnancy
- after pregnancy is acknowledge, most are due to genetic abnormalities
Risks: environmental factors, maternal age, health conditions
