Development Lecture Flashcards
Development
Gradual modification of anatomical structures and physiological characteristics from fertilization to maturity
Amphimixis
-Fusion of female pronucleus and male pronucleus
-Moment of conception
-Cell becomes a zygote with 46 chromosomes
-Fertilization is complete
Cleavage
-Sequence of cell divisions begins immediately after fertilization
-Zygote becomes a pre-embryo, which develops into multicellular blastocyst
-Ends when blastocyst contact uterine wall
Blastomeres
Identical cells produced by cleavage divisions
Morula
-Stage after three days of cleavage
-Pre-embryo is solid ball of cells resembling mulberry
-Reaches uterus at about day 4
Blastocyst
-Formed by blastomeres
-Hollow ball with an inner cavity (known as blastocoel)
Trophoblast
-Outer layer of cells separate outside world from blastocoel
-Cells responsible for providing nutrients to developing embryo
Inner cell mass-Embryoblast
-Clustered at end of blastocyst
-Exposed to blastocoel
-Insulated from contact with outside environment by trophoblast
-Will later form embryo
Implantation
-Begins with attachment of blastocyst to endometrium of uterus
-Sets stage for formation of vital embryonic structures
-Occurs in the fundus of body of uterus
-Ectopic pregnancy occurs outside of uterus
-Occurs six to seven days after fertilization
-Blastocyst adheres to uterine lining
-Trophoblast cells divide rapidly, creating several layers that are going to support the embryo as it develops
Ectopic Pregnancy
-Does not produce viable embryo
-Can be life threatening
Gastrulation
-Germ Layer Formation
-Formation of third layer of cells
-Cells in specific areas of surface move toward central line known as primitive streak
Extraembryonic Tissue Formation
Support embryonic (embryonic period) and fetal development (fetal period)
Primitive Streak
-Migrating cells leave surface and move between two layers
-Creating three distinct germ layers
Ectoderm
Consists of the superficial cells that did not migrate into interior of inner cell mass
Endoderm
consists of cells that face blastocoel
Mesoderm
consists of poorly organized layer of migrating cells between ectoderm and endoderm
Embryonic Trilaminar Disc
-Oval, three-layered sheet
-Produced by gastrulation
-Will form body of embryo
-> Rest of blastocyst will be involved in forming extraembryonic tissues
Yolk sac
nutrient source until placenta forms
Amnion
sac that fills with fluid and forms a protective cushion
Allantois
will eventually form the urinary bladder of the embryo
Chorion
will form the placenta
