Histology - Pre-Embryonic - Reverse Flashcards
mitotic divisions that form cells called blastomeres
Cleavage
tighter blastomere intercellular adhesion forms morula, results in the formation of an inner and outer cell mass.
Compaction
uterine fluid pumped into morula forms blastocyst
Cavitation
blastocyst hatches from the zona pellucida
Hatching
blastocyst implants in endometrium of uterine wall
Implantation
Mitotic nondisjunction during cleavage, generally less severe; e.g., mosaic Down syndrome
mosaicism
gives rise to the embryo (inner cell mass)
embryoblast
gives rise to the fetal placenta (outer cell mass). cytotrophoblast, syncytiotrophoblast, vascular lacunae
trophoblast
end with embryoblast
Embryonic pole
end opposite embryoblast
Abembryonic pole
blastocyst hatches from zona pellucida (ZP prevents implantation)
Hatching
trophoblast at embryonic pole invades the endometrium on DAY 6
Implantation
- Implantation completed: uteroplacental circulation is established 2. Bilaminar disc formed: embryoblast differentiates into 2-layered disc
Week 2: Events
- cytotrophoblast 2. syncytiotrophoblast (part of chorion)
trophoblast becomes:
- epiblast 2. hypoblast (form the fetus, amnion, and part of chorion)
Embryoblast becomes:
mitotic cells that give rise to the syncytiotrophoblast.
Cytotrophoblast
the epithelial covering of the highly vascular embryonic placental villi, which invades the wall of the uterus to establish nutrient circulation between the embryo and the mother. It forms the syncytium that erodes endometrium and its vessels.
Syncytiotrophoblast
maternal blood
vascular lacunae
nutrition from maternal blood 1. uteroplacental circulation 2. implantation bleeding
nutrition from uterine gland secretions give way to
human chorionic gonadotropin (hCG) that maintains progesterone secretion in the ovaries to promote uterine blood flow that sustains embryonic and fetal growth. Linked to emesis gravidarum (morning sickness).
Syncytiotrophoblast secretes
hCG serum level elevation at day 8
Pregagncy test dectects
implantation outside of the uterine body, most commonly in the unterine tube - “tubal pregnancy” - 95%+ of ectopic prenancies in uterine tube.
Ectopic pregnancy
implantation over or near the cervical opening (internal os), usually presents late in pregnancy
Placenta previa
trophoblast implants, but embryoblast is absent/incomplete. May produce a benign tumor called a hydatidiform mole. Elevated hCG secretion.
Molar pregnancy
malignant tumor of the trophoblast. Elevated hCG secretion.
Choriocarcinoma
one of the membranes that exist during pregnancy between the developing fetus and mother, formed by extraembryonic mesoderm and the two layers of trophoblast and surrounds the embryo and other membranes. Chorionic villi emerge from the chorion, invade the endometrium, and allow transfer of nutrients from maternal blood to fetal blood.
Chorion
the inner layer of the trophoblast. It is interior to the syncytiotrophoblast and external to the wall of the blastocyst in a developing embryo.
cytotrophoblast
embryoblast undergoes lamination to form two layers, hypoblast and epiblast
Bilaminar disc
cells divide/migrate to line the blastocyst cavity. blastocyst cavity becomes the primary (primitive) yolk sac.
Hypoblast
a tissue type derived from the inner cell mass of the blastocyst. It lies above the hypoblast, and undergoes cavitation whereby the amniotic cavity (AC) is formed. It differentiates to form all three layers of the trilaminar germ disc (ectoderm, mesoderm, and endoderm) during gastrulation.
epiblast
a short lived combination of hypoblast cells and extracellular matrix. At day 9-10 of embryonic development, cells from the hypoblast begin to migrate to the embryonic
exocoelomic membrane
forms adjacent to the hypoblast, and spaces appear in it which unit to form the large chorionic cavity (CC).
Extraembryonic mesoderm (EM)
“pinched off” from the pYS (primary yolk sac)
secondary (definitive) yolk sac (sYS)
hypoblast cells which have migrated to line the blastocyst cavity. It later becomes secondary yolk sac after part of it is pinched off. Thereafter its remnants degenerates.
Primary yolk sac
Zygote formed after fertilization in ampulla of uterine tube
Day 1
Morula enters uterus
Day 4
Implantation of blastocyst begins
Day 6
Positive pregnancy test, detectable hCG levels.
Day 8
- Implantation completed (uteroplacental circulation established) 2. Bilaminar disc formed (hypoblast & epiblast appear).
End of Week 2
Extraembryonic mesoderm + cytotrophoblast + syncytiotrophoblast
chorion =
blastocyst cavity, embryoblast, trophoblast, embryonic/abembryonic poles
Blastocyst
gastrulation, neuralation, body folding
Week 3 Events
Loosely arranged, migratory. formed via epithelial-mesenchymal transformation at the primitive streak & node
mesenchymal cells
sites of epiblast invagination. regress & degenerate at the end of week 4 when gastrulation completes.
Primitive streak and node
head-tail axis
Cephalocaudal
front-back axis
Ventral-dorsal
Cephalocaudal, Ventral-dorsal, left-right
body axes
future mouth
oropharyngeal membrane
future anus
cloacal membrane
structure which includes the transformation of the neural plate into the neural tube. induces formation of neural tube (future brain, spinal cord)
Neurulation
failure of rostral neuropore to close
Anencephaly
failure of caudal neuropore to close
Spina bifida
Forms gut tube from endoderm and mesoderm around the secondary yolk sac. Also forms intraembryonic cavity.
Lateral body folding
becomes thoracic and abdominopelvic cavities, froms during lateral body folding
intraembryonic cavity
Relocates primitive mouth and heart to adult position, is driven by longitudinal growth of the neural tube
Cephalocaudal body folding
helps the embryo exchange gases and handle liquid waste.
Allantois
Tail regresses, limbs elongate & rotate, digits appear; face develops. Organogenesis. Greatest risk of birth defects in week 5.
Week 4 to 8
gametes and epithelial cells lining digestive organs, respiratory airways, and some urogenital passages.
Endoderm
epidermis & its derivatives (hair, nails, glands)
Surface Ectoderm
neural tube gives rise to the brain and spinal cord.
Neuroectoderm
differentiates into somites (somitomeres in head region), becomes dermis, skeletal muscle, vertebrae & ribs. lateral to (at the side of) the neural tube.
Paraxial Mesoderm
urogenital system (majority)
Intermediate mesoderm
CT of body wall & limbs
Lateral plate mesoderm (parietal layer)
GI/respiratory organs (excelpt epithelial lining)
Lateral plate mesoderm (visceral layer)
fluid rich ECM with multipotent mesenchymal cells
Mesenchyme
bilaterally paired blocks of paraxial mesoderm that form along the anterior-posterior axis of the developing embryo. They give rise to sclerotome, myotome, dermatome for each body segment.
Somites
cleveage, compaction, morula formed, cavitation, blastocyst formed, zona pellucida hatching, implantation initiated
Week 1 Cellular Events
axial skeleton
sclerotome
dermis
dermatome
skeletal muscle
myotome
