Embryology and Development Flashcards
ovulation
14 days into ovarian cycle, 1 oocyte is released into oviduct
where do sperm get deposited
cervix
where does fertilization occur
ampullary region of uterine tube
3 steps in fertilization
1) sperm penetrates corona radiata
2) sperm penetrates zona pellicuda
3) fusion of sperm/ oocyte membranes
fertilization results
diploid zygote with homologous pair of chromosomes
gender determination
based on the sperm since oocyte always has an X chromosome, (y for boy, x for girl)
cleavage initiation
cleavage occurs by actin filaments to form 2-cell stage
morula
3 days, ball of blastomeres, 12-16 cells, cytoplasm divides but no growth in size of ball, looks like a blackberry
blastocyst
hollow sphere of cells, 5 days post-fertilization
-hollow cavity = blastula
inner cell mass
forms inside blastocyst, pluripotent stem cells that have not differentiated
what does the inner cell mass develop
embryo, amnion, yolk sac, allantois
implantation
blastocyst/morula is pushed along fallopian tube until it enters uterus
-implants into endometrium
- 6 days old
abnormal implantation
-ectopic pregnancy
-ovarian
-cervical
-interstitial
-peritoneal
-tubal
infundibular
at the end of week 1, day 7, what do we have
blastocyst with inner cell mass, developing syntrophoblast and cytrophoblast
two general layers in week 2
trophoblast and embryoblast
trophoblast
outside of ball that provides nutrients to embryo
-differentiates to cytotrophoblast and syncytiotrophoblast
embryoblast
ICM, forms epiblast and hypoblast
what 2 cavities form in week 2
yolk sac and amniotic sac
what 2 layers does the extraembryonic mesoderm split into
somatic and splanchnic
cytotrophoblast
inner layer of trophoblast
- mononucleated
-migrate into syncytiotrophoblast where they fuse and loose all their membrane
synctiotrophoblast
outer layer of trophoblast, multinucleated
-invades into uterine wall
-produces hCG (human chorionic gonadotropin)
hypoblast
small cuboidal cells
-partially contributes to yolk sac
-remainder degenerates via apoptosis
epiblast
high columnar cells
-adjacent to amniotic cavity
-where embryo is derived from
-thickens to form primitive streak
what develops from trophoblast on Day 9
trophoblastic lacunae
-vacuoles in synctiotrophoblast that fuse together
exocoelomic cavity (yolk cavity)
lines cytotrophoblast
-forms primitive yolk sac
amniotic cavity
sac that contains amniotic fluid
amniocentesis
needle used to withdraw amniotic fluid in order to diagnose chromosomal abnormalities
yolk sac
useful in the beginning of development until placenta develops, disintegrates over time
-first site of blood cell formation
extraembryonic splanchnic mesoderm
inner layer, covers yolk sac
extraembryonic somatic mesoderm
outer layer of mesoderm, lines cytotrophoblast and amnion
maternal sinusoids
congested and dilated capillaries
-maternal blood enters lacunar system
exocoelomic cyst
day 13, portions of exocoelomic cavity pinched off during formation
connecting stalk
where mesoderm transverses chorionic cavity (becomes umbilical chord)
chorionic cavity over time
at 13 days is the largest cavity
-is gone by the 3rd month
yolk sac over time
at 13 days is middle sized
-by 3rd month its totally gone
amniotic cavity over time
starts out small
-by the end of the 3rd month is the largest fluid filled cavity
trophoblastic lacunae cause what at the end of week 2
implantation bleeding
gastrulation
3 germ layers are formed: endoderm, mesoderm, ectoderm
ectoderm
-neural system
-skin, epidermis
-eyes
-ears
mesoderm
-musculoskeletal tissues
-genitourinary system
-body wall membrane
-membranes that line cavities
-dermis
endoderm
-foregut
-midgut
-hindgut
-GI tract
-liver
-pancreas
-respiratory tract
-bladder
embryonic disk
formation of primitive streak on surface of epiblast
what cells migrate into primitive node
epiblast cells
invagination
cells displace in hypoblast to creat endoderm
-the ones that lie b/w epiblast and endoderm make mesoderm
-cells remaining in epiblast form the ectoderm
how is the body plan refined during gastrulation
oropharyngeal membrane (future mouth) and cloacal membrane (future anus) forms
teratogenesis
-alcohol and genetics
-during gastrulation
-holoprosencephaly
holoprosencephaly
injury to the anterior midline of germ disc
-“cyclopia”
-one eye, cleft palate, close eyes
caudal dysgenesis
injury to caudal aspect of the germ disc
-genetics and environment
-affects lower limbs and urogenital area
mermaid syndrome
sacrococcygeal tumors
remnant of primitive streak
-clusters of pluripotent stem cells proliferate and form tumores
conjoined twins
issues with spitting of primitive node
anatomical position
standing straight up, palms facing forward, head looking straight
migration patterns of epiblasts
-caudal to cranial
-medial to lateral
fate map
established during gastrulation, determines which section will develop into what parts of the body
notochord
mesoderm derivative, precursor to axial skeleton
-forms nucleus pulposus of intervertebral discs
-vertebral bodies form around notochord
somite formation
mesoderm gives rise to paraxial mesoderm (future somites)
-mesoderm -> paraxial mesoderm-> parietal/visceral mesoderm layers ->somite
somite
cells formed in segmental pairs along neural tube from paraxial mesoderm
-differentiate into vertebrae, muscles of back and body, and dermis of the skin
neurulation
1) notochord forms mesoderm after gastrulation
2) signals from notochord cause inward folding of ectoderm around neural plate
3) ends of neural plate fuse and disconnect to form an autonomous neural tube
embryonic folding (sagittal)
-embryonic disk starts flat
-caudal and cranial region start to fold
fertilization vs. gestational age
-fertilization begins at conception
-gestational age begins 2 weeks earlier, at the beginning of last period
critical period for development
period of maximum sensitivity to abnormal development
-3-8 weeks = formation of organs
birth defect
congenital malformation (physical anomaly)
congenital disorder
a condition that exists at birth or before birth, or develops first month of life
teratology
study of causes and biological processes leading to abnormal development
teratogen
any substance causing a birth defect
thalidomide
old drug in Germany used to help pregnant women with nausea
-shut down blood vessels, leaving babies with deformed limbs (phocomelia)
who is most susceptible to congenital abnormalities
-maternal age
-environmental factors
-genetic predisposition
-unknown
