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Anat - Zygotic Per.

The Zygotic Period

Morula day 3-4 where there are 16-32 cells clumped in a ball
inner cell mass the "embryoblast" - pluripotent cells that make only embryonic cells. first apparent in blastocyst at the embryonic pole
outer cell mass develops into placental membranes (tropholast
trophoblast peripheral cells of blastocyst that attach the fertilized ovum to the uterine wall and contribute to placenta membranes to nourish embryo
Describe how the morula transitions into the blastula stage. Differential cell adhesion and junctions cause outer cells to become convex & inner concave (compaction), causes inner cell mass and outer cell mass to form. ion pumps fluid into the center to form the blastocyst cavity
totipotent vs. pluripotent totipotent can make ANY cell type (ex: morula cells) Pluripotent - can make a limited subset of cells (ex: inner cell mass can only make embryonic cells, not trophoblast cells)
2 ways to form Chimeras (1)combining 2+ morulas into a giant morula and allowing to develop into adult with 2 different cell types (2)inject morula cell into inner cell mass of another blastula so areas of the body would contain different cell type (ex black/white chimera mice)
embryonic stem cells cells from the inner cell mass that are cultured so they will continually divide and remain pluripotent; can be used to form chimeras where they eventually contribute to formation of all tissues
What are Barr bodies and when are they formed? condensed inactive X chromosome found in females. Inactivation occurs during the formation of the morula and blastula
Why is X inactivation important in diagnosing x-linked inherited disorders if males carry the x-linked gene, they will have the full form the of the disease. Females will only have the full disease if they are homozygous for the gene. heterozygous females are "chimeric" and show partial symptoms(ex Duchenne muscular dystrophy)
When does implantation begin? Day 5-6. By day 9, zygote is completly penetrated
What are ectopic pregnancies and where can they occur? implantation outside the uterus - most occur in uterine tube ("tubal pregancy"). Also occur in ovary or abdomen
placenta previa placenta covers the internal os (cervical opening) of the uterus - causes bleeding during pregnancy and premature separation of the placenta from the uterus
Decidua reaction rxn that occurs when hatched blastocyst binds the endometrium & cause endometrial cells to secrete nutrients, increase uterine glands and vasculture, and edema to support the embryo
What are the 2 layers of the trophoblast (outer cell mass) and what do they release cytotrophoblast (inner layer of mononucleated cells) and syncytiotrophoblast (outer layer of multinucleated cells that make hCG)- both secrete enzymes to invade uterine lining
Describe the fate of the inner cell mass at day 7-8 forms a bilaminar disk with a hypoblast layer next the to blastocyst cavity and an epiblast layer on the opposite side
what is the amniotic cavity cavity that forms between the cytotrophoblasts and epiblasts; eventually becomes lined by epiblasts
How is the primitive (primary) yolk sac formed exocoelomic (Heuser's) membrane forms from migrating hypoblast cells. Heuser and hypoblast cells together line the inner surface of the blastocoel cavity to convert it into the primary/primitive yolk sac
extraembryonic reticulum loose extracellular matrix deposited between the heuser's membrane and cytotrophoblast in the primitive yolk sac
primitive (primary) vs definitive (secondary) yolk sac secondary yolk sac forms after the primitive sac when migrating hypoblasts push the Heuser (exocoelomic) membrane away causing the primitive yolk sac to pinch away. Secondary sac remains attached to bilaminar disc while primary eventually disintegrates
what is extraembryonic mesoderm cells that form between Heuser's (exocoelomic) and cytotrophoblast cells. Forms extraembryonic splanchnic mesoderm (covers Heuser's membr.) and extraembryonic somatic mesoderm (covers cytotrophblast and amnion)
what is the extraembryonic coelom spaces that form in extraembryonic reticulum that eventually combine to form one large cavity
how is the future umbilical cord formed extraembryonic coelom grows so large that the embryo is attached by only a stalk of cells (connecting stack) that eventually becomes the umbilical cord
Describe early uteroplacental ciruculation at day 11-13, lacunae form in the syncytiotrophoblast and erode the maternal capillaries (called "maternal sinuses") in the endometrium. The lacunae combine and fill with blood to establish circulation
Created by: c.phill