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WVSOM - Embryology-3

Trilaminar Stage

Hensen's node Serves as organizer, secreting growth factors that induce tissue type differentiation and embryogenic patterning
Primitive pit Pore in center of Hensen's node
Primitive streak (day 15 - week 4) Faint white trace at caudal end of embryonic disc, formed by movement of cells at onset of mesoderm formation and providing 1st evidence of embryonic axis
Primitive ridges Ridge that bounds the primitive groove in early stages of embryonic development
Primitive groove Lengthwise median furrow in primitive streak of the embryo
Situs inversus Developmental defect when viscera in abnormal left-right orientations; probably results from defective GF genes secreted from embryonic organizer (i.e. Hensen's node)
Partial situs inversus Some organs are in opposite orientations; can be fatal
Total situs inversus All organs are transposed; little to no clinical consequences
Primitive streak expansion, regression Begins at caudal end of germ disc; elongates towards cranial end (until day 18); extends across ~2/3 length of germ disc; streak regresses, completely disappearing by 4th week
Grastrulation First movement of embryonic cell populations, serving to compartmentalize embryo into 3 germ layers - ectoderm, endoderm, mesoderm
How is gastrulation accomplished? With the primitive streak
What cells invaginate to form the primitive groove along the caudal medial line? Epiblastic cells
Endoderm (intraembryonic endoderm) Cells that have wedged into hypoblast (from the invagination and separation of cells form the epiblast); eventually, endoderm completely replaces hypoblast by pushing it out of germ disc and into yolk sac
Mesoderm Invaginating cells (from the epiblast) that do not wedge into the hypoblast
Ectoderm Epiblastic cells that do not pass through the primitive streak
From what are all three germ layers derived? Epiblast
What gives the germ disc a pear shape perimeter? The cells that migrate into the space between the epiblast and hypoblast spread in lateral and cranial directions
What plate do the cells that move in the cranial direction form? Cardiogenic (heart forming) plate
What else can the cranial migrating cells generate? The notochord
Which cells reach the cranial extremities first? The first cells to pass through the streak; caudual mesoderm and endoderm = younger, differentiation slightly delayed; embryos tend to develop from cranial end towards caudal
Sacrococcygeal teratomas Develop when primitive streak fails to regress; most common newborn tumors; derived from pluripotent cells; consist of misture of different cell types; tumors can usually be surgically removed
Caudal dysgenesis Underdevelopment of caudal features due to insufficient mesoderm in caudal-most region of embryo
Symptoms/abnormalities of caudal dysgenesis Hypoplasia, fusion of lower limbs, vertebral abnormalities, renal agenesis, imperforate anus, anomalies of genital organs
Sirenomelia Extreme condition of caudal dysgenesis; legs fused to produce mermaid-like fetus; common teratogenic factor = maternal diabetes
Notochord Hollow, cartilaginous rod that extends through midline; phylum named after it (Chordata)
Notochord's role in vertebrates Organizer
What is the notochord derived from? Hensen's node
What differentiation does the notochord control? Neural tube, somites
What happens to the notochord after it has served its purpose? Majority of it degenerates by apoptosis; some notochordal derived cells persist in adult as nuclei pulposus of intervertebral discs
Formation of notochord Epitblast cells that invaginated thru primitive pit remain contiguous, extend in cranial direction to form hollow tube (notochordal process), lumen of tube = notochordal canal
What region prevents the continuation of the notochordal process? Prechordal plate (progenitor of mouth); regions contains hypoblast & epiblast celss that block further progression of process; at this point, primitive streak regression commences; occurs around day 18
What does the notochord fuse with? Underlining endoderm
What results from the fusion of the notochord with the underlining endoderm? Opening to yolk sac; transitory channel (via primitive pit) connects amniotic cavity & yolk sac
What is the connection between the amniotic cavity & yolk sac called? Neurenteric canal
The tubular process that has been flattened is called ... Notochordal plate
The notochordal plate folds (reforming a tube), starting at the cranial end & progressing towards the caudal end Notochord
What happens when the notochord detaches from the yolk sac endoderm? The neurenteric canal closes
Created by: JaneO



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