Conception, Pregnancy, Fetal Development Flashcards
oogenesis - overview
*differentiation of the ovum
*occurs in the female fetus prior to their birth
oogenesis - steps
- primary oocytes
- begin meiosis 1 during fetal life
- PAUSE (meiosis 1 arrested in prophase 1 for years until ovulation - still a primary oocyte)
- complete meiosis 1 prior to ovulation (now a secondary oocyte)
- meiosis 2 arrested in metaphase 2 until fertilization
- if fertilization does not occur within 1 day, secondary oocyte degenerates
blastocytosis - overview
*transition from a zygote (after fertilization) into a fetus
*zygote (fertilized ovum) → blastomere (2-cell) → morula → blastocyst
*58-cell blastocyst differentiates into 5 embryo-producing cells (inner cell mass) and remaining cells (53 cells) become placental trophoblasts
early fetal development - week 1
*hCG secretion begins upon implantation (usually days 6-10) of the blastocyst
early fetal development - week 2
*bilaminar disc formed (2 layers in week 2- epiblast & hypoblast)
epiblast becomes embryo
hypoblast becomes yolk sac
early fetal development - week 3
*gastrulation: formation of trilaminar disc (3 layers in week 3 - endoderm, mesoderm, ectoderm)
early fetal development - weeks 3-8 (overview)
neural tube** forms; closes by week 4
**organogenesis occurs
*extremely susceptible to TERATOGENS
early fetal development - week 4
*HEART begins to beat
*upper and lower limb buds form
*“4 limbs & 4 heart chambers in week 4”
note - heart beat is not yet detected on ultrasound or doppler
early fetal development - week 6
*cardiac activity on transvaginal ultrasound
recall: heart starts to beat at 4 week, but undetectable until week 6
early fetal development - week 8
*fetal movement begins
early fetal development - week 10
*genitalia female/male characteristics form
important teratogens & susceptibility period
*during the embryonic period (weeks 3-8) the fetus is extremely susceptible
*meds: ACE inhibitors, aminoglycosides, antiepileptic drugs, folate antagonists, isotretinoin, warfarin
*substances: alcohol, cocaine, nicotine, etc
*other: iodine (lack or excess), maternal diabetes, mercury, X-rays
placenta - overview
*primary site of nutrient and gas exchange between mother and fetus
*2 components: fetal & maternal
placenta - maternal component
*aka decidua basalis
*derived from endometrium
*maternal blood is found in the lacunae
placenta - fetal component
- cytotrophoblast - inner layer of chorionic villi
- syncytiotrophoblast - outer layer of chorionic villi
*synthesizes & secretes hormones (hCG)
*lacks MHC-1 expression
diffusion across the placenta
*umbilical vein carries oxygenated blood to the fetus; umbilical artery carries blood from fetus back to mother
*placental villi increase surface area for diffusion
*blood traveling from mother to fetus: high in O2 / nutrients, low in CO2 / waste
*fetal blood returning to mother: low in O2 / nutrients, high in CO2 / waste
umbilical cord - overview
*2 umbilical arteries, carrying deoxygenated blood away from the fetus and back to mom
*1 umbilical vein, carrying oxygenated blood from mom to fetus
*Wharton jelly surrounds the arteries/veins in the umbilical cord to protect them from compression
formation of the umbilical cord
*yolk sac (3rd week) → allantois → urachus
*urachus = duct between fetal bladder and umbilicus
urachus abnormalities
- patent urachus: COMPLETE failure of urachus to obliterate → urine discharge from umbilicus
- urachal cyst: PARTIAL failure of urachus to obliterate → fluid-filled cavity lined with uroepithelium between umbilicus and bladder
- vesicourachal diverticulum: SLIGHT failure of urachus to obliterate