Embryology & Pregnancy Physio Flashcards
How many days after fertilization is pituitary LH stimulating luteal cells to secrete progesterone & estrogen in preparation for implantation
10 days
What happens to the trophoblastic cells on day 5 of fertilization
they begin to secrete hCG which will take over for the luteal hormones completely by day 10
What does the B subunit of fetal hCG do
stimulates corpus luteum to secrete progesterone & estrogen
When does fetal hCG peak during pregnancy
in the first 3 mos
What is measured as an index of fetal well-being
estriol, th emain placental estrogen
What are the peripheral effects of hormonal changes during the 4th+ months of pregnancy
- massive growth of the uterus (myometrium)
- increased growth of all components of the breast
- estrogen/progesterone primarily secreted by the placenta
What is measured as an index of placental well-being
hPL (human placental lactogen)
- increases maternal lipolysis & ketogenesis
- decreases maternal energy stores
- anti-insulin actions (gestational DM)
Which peptide hormone secreted by the ovaries during pregnancy is responsible for distention of the pubic symphysis, cervix, & vagina
Relaxin (non-essential: this will still happen in the absence of ovarian secretion)
Describe the role of oxytocin near the end of pregnancy
- receptors in the myometrium increase in response to elevated plasma estrogens
- elevated oxytocin causes uterine prostaglandin secretion to increase (which causes uterine contractions)
Describe the process by which a spontaneous abortion occurs in fetal demise
toxic products from the fetus increase prostaglandin release from the uterus which initiate contractions & spontaneous abortion
describe the interaction of estrogen in lactation
- high estrogen increases prolactin secretion
- estrogen blocks milk synthesis (estrogen drops during parturition/childbirth which withdraws the block on milk synthesis)
Describe how lactation is maintained
- suckling stimulates nipple receptors & transmits to hypothalamus
- oxytocin & PRL released & GnRH decreased (which decreases FSH & LH)
- decreased FSH & LH lead to decreased estrogen
- decreased estrogen leads to anovulation and amenorrhea
Define fertilization
Fusion of an ovum and spermatozoon to form a single cell/zygote
- occurs within 24 hrs after ovulation
- goals: restores diploid chromosomes, determines sex, initiates cleavage
List the gestational periods
- Germinal period: 1st - 3rd weeks of development
- Embryonic period: 4th - 8th weeks of development (most organ/tissues formed & 3 germ layers differentiate)
- Fetal period: 9th week to term (rapid fetal growth, placental development completed)
What are the main components of the germinal period (1st-3rd weeks)
- cleavage
- morula formation (12-16 cell stage)
- blastocyst formation
- implantation
- trophoblast & chorion differentiate
How many hours after fertilization does it take to reach the 16-cell stage of cleavage
96 hours after fertilization
Describe the type of cell the zygote becomes at the 16-cell stage of cleavage
Morula
- Inner cells: embryo proper
- Outer cells: trophoblast
- Zona Pellucida: membrane surrounding oocyte, prevents polyspermia & ectopic implantation, disappears at the end of the 5th day of fertilization
Describe implantation of the blastocyst
embeds in the anterior/posterior wall of uterus near the fundus in the functional layer of the endometrium
- end of 1st week
- during secretory phase (high progesterone)
- endometrium now known as decidua!!!
Describe the divisions of the decidua
- Decidua basalis
- Decidua capsularis (ruptures during labor)
- Decidua parietalis
Summarize the 2nd week of development of a fetus/zygote
Week of 2s
- trophoblast differentiates into 2 layers (syn/cytotrophoblast)
- embryoblast forms 2 layers (epiblast & hypoblast)
- extraembryonic mesoderm splits into 2 layers (somatic & splanchnic layers)
- Formation of 3 cavities: amniotic, yolk sac, & chorionic cavities
When does the primitive streak appear
at day 15
- caudal end of germ disc on epiblast
- groove containing pluripotent cells
- gastrulation = differentiation of cells in streak
What is the source of all three germ layers
the epiblast
- gives rise to all tissues & organs of the embryo
- differentiates into buccopharyngeal membrane, cloacal membrane, notochord (neural tube)
What happens if the allantois/allantoenteric diverticulum remains patent
Leakage of urine through the umbilicus
Describe the pathophysiology of caudal dysgenesis aka sirenomelia aka mermaid syndrome
insufficient mesoderm in the caudal region
