Flashcards in Histology - Pre-Embryonic - Reverse Deck (70)
mitotic divisions that form cells called blastomeres
tighter blastomere intercellular adhesion forms morula, results in the formation of an inner and outer cell mass.
uterine fluid pumped into morula forms blastocyst
blastocyst hatches from the zona pellucida
blastocyst implants in endometrium of uterine wall
Mitotic nondisjunction during cleavage, generally less severe; e.g., mosaic Down syndrome
gives rise to the embryo (inner cell mass)
gives rise to the fetal placenta (outer cell mass). cytotrophoblast, syncytiotrophoblast, vascular lacunae
end with embryoblast
end opposite embryoblast
blastocyst hatches from zona pellucida (ZP prevents implantation)
trophoblast at embryonic pole invades the endometrium on DAY 6
1. Implantation completed: uteroplacental circulation is established 2. Bilaminar disc formed: embryoblast differentiates into 2-layered disc
Week 2: Events
1. cytotrophoblast 2. syncytiotrophoblast (part of chorion)
1. epiblast 2. hypoblast (form the fetus, amnion, and part of chorion)
mitotic cells that give rise to the syncytiotrophoblast.
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.
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).
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.
implantation over or near the cervical opening (internal os), usually presents late in pregnancy
trophoblast implants, but embryoblast is absent/incomplete. May produce a benign tumor called a hydatidiform mole. Elevated hCG secretion.
malignant tumor of the trophoblast. Elevated hCG secretion.
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.
the inner layer of the trophoblast. It is interior to the syncytiotrophoblast and external to the wall of the blastocyst in a developing embryo.
embryoblast undergoes lamination to form two layers, hypoblast and epiblast
cells divide/migrate to line the blastocyst cavity. blastocyst cavity becomes the primary (primitive) yolk sac.
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.
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
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
Morula enters uterus
Implantation of blastocyst begins
Positive pregnancy test, detectable hCG levels.
1. Implantation completed (uteroplacental circulation established) 2. Bilaminar disc formed (hypoblast & epiblast appear).
End of Week 2
Extraembryonic mesoderm + cytotrophoblast + syncytiotrophoblast
blastocyst cavity, embryoblast, trophoblast, embryonic/abembryonic poles
gastrulation, neuralation, body folding
Week 3 Events
Loosely arranged, migratory. formed via epithelial-mesenchymal transformation at the primitive streak & node
sites of epiblast invagination. regress & degenerate at the end of week 4 when gastrulation completes.
Primitive streak and node
Cephalocaudal, Ventral-dorsal, left-right
structure which includes the transformation of the neural plate into the neural tube. induces formation of neural tube (future brain, spinal cord)
failure of rostral neuropore to close
failure of caudal neuropore to close
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
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.
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.
epidermis & its derivatives (hair, nails, glands)
neural tube gives rise to the brain and spinal cord.
differentiates into somites (somitomeres in head region), becomes dermis, skeletal muscle, vertebrae & ribs. lateral to (at the side of) the neural tube.
urogenital system (majority)
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
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.
cleveage, compaction, morula formed, cavitation, blastocyst formed, zona pellucida hatching, implantation initiated
Week 1 Cellular Events