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
Describe the pathophysiology of sacrococcygeal teratoma
remnants of primitive streak in the sacrococcygeal region forming a tumor of pluripotent cells that produce a teratoma
Describe the pathophysiology of anencephaly
failure of closure of the neural tube at the cranial region
Describe the pathophysiology of spina bifida
failure of closure of the neural tube at the cervical to caudal region
List some derivatives of the ectoderm
- nervous system
- hypophysis
- mammary & cutaneous glands
- epidermis, hair, nails
- sensory epithelium of eye, ear, nose
- epithelium of sinuses, oral & nasal cavities
- tooth enamel
- intra oral glands
What forms from the sclerotome
- base of skull
- vertebral column & ribs
- most of the calvaria (skull vault)
What forms from the dermatomyotomes
- dermis of skin & back
- muscles of back
- body wall
- some limb muscles
What does the intra-embryonic coelom give rise to (from lateral plate mesoderm)
pericardial, pleural, peritoneal cavities
The intermediate mesoderm differentiates into what system
urogenital system
What does the primitive yolk sac from the endoderm differentiate into
primitive gut
Describe the 5 major divisions of the primitive gut
- pharyngeal gut = tympanic cavity, auditory tube, tonsils, thymus, mouth, tongue, pharynx, thyroid, parathyroid
- foregut = esophagus, stomach, part of duodenum, liver, gallbladder, pancreas, lining epi of the trachea, bronchi, lung
- midgut = duodenum, small intestine, appendix, ceacum, ascending colon, R 2/3 of transverse colon
- hindgut = L 1/3 of transverse colon, descending & sigmoid colon, rectum
- cloaca = rectum, anal canal, bladder except trigone, urethra, genital tracts
