The Embryonic Period Flashcards
What is the extraembryonic mesoderm?
A new layer of cells derived from the epiblast and yolk sac that is found between (and SURROUNDING) the two. It separates the embryo from uterine tissue, is important in forming the placenta and gives mechanical and trophic support. It attaches to the CYTOTROPHOBLAST through holes in it.
What are the trophoblastic lacunae?
holes in the uterine tissue that allow blood flow and oxygen diffusion to the blastocyst.
What is the choreon?
Consists of the syncytiotrophoblast, cytotrophoblast and XE somatic mesoderm. It is the fetal contribution to the placenta.
When are the yolk sac and amniotic cavity formed?
After implantation. The yolk sac, hypoblast and epilast form the blimainar geminal disc; the amniotic cavity is also formed.
What is the bilaminar disc?
A series of epiblast and hypoblast cells that form a border between the yolk sac cavity and the amniotic sac cavity.
When does the XE mesorderm form?
After the amniotic sac and yolk sac form. The maternal vessels also start to enter the trophoblastic lacunae.
When does the xe coelom form?
After the XE mesoderm. As it forms, uteroplacental circulation begins.
What is a complete mole?
A dipoloid zygote that has only paternal chromosomes; the gg lost its chromosomes by 2 sperm or 1 sperm replicated itself. No fetal tissue present.
What is apartial mole?
Fertilization of the haploid ovum and duplication of the paternal haploid chromosomes. Fetal tissue (w/maternal chromosomes) is present.
What period of embryogenesis is immune to teratogens?
Pre-embryonic period
What occurs during the embryonic period?
major body systems develop, embryo folds, CNS develops, laternal folding of amnion/body wall.
Gastrulation
begining of morphogenesis. An embryonic disk is formed and the germ cells are differentiated into the endoderm, mesoderm and ectoderm. The PRIMITIVE STREAK is also formed.
What is the primitive streak?
A narrow line of cells that forms on the surface of the embryonic disk. It is the future axis of the embryo, and marks the beginning of GASTRULATION. The region will also be the back end of the fetus.
Primitive groove
posterior end of the primitve streak where epiblast cells migrate to, fall through and then spread out. This elongates the embryonic disc and forms the MESODERM and ENDODERM.
What layer does the endoderm replace?
hypoblast
What layers are derived from the epiblast?
ectoderm, mesoderm and endoderm
What replaces the primitive streak?
Notochord
primitive pit
anterior end of the primitive streak in the center of the embryonic disk.
sacrococcyeal teratoma
disorder that occurs when the primitive streak does not recede. A tumor with derivatives of all 3 germ layers is present in the embryo/infant.
caudal dysplasia
A germ layer disorder (mesoderm) in which the lower vertebrae and sacrum do not develop correctly.
How is the notochord formed?
Migrating cells form a median column of cells in the mseoderm; looks like a rod and serves as the axis for the embryo.
What does the notochord do?
Acts as an axis which things develop around, is a foundation upon which the vertebral column forms and brings about induction of the NEURAL TUBE.
Chordoma
Bone cancer in adults that derives from remnants of the embryonic notochord.
What does the notochord induce?
The ectoderm to produce epithelial ectoderm (outermost skin) and the neural plate (nervous system) and eventually the neural tube.
