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Video-Overview of Human Prenatal Development
Sep 2, 2024
Human Prenatal Development
Stages of Development
Pre-embryonic Stage
Embryonic Stage
Fetal Development
Fertilization Process
Occurs in the ampulla of the fallopian tube.
Fertilized egg, or conceptus, travels to the uterus.
Undergoes mitotic divisions to form blastomeres (cleavage).
Conceptus Development
Day 3
: Conceptus reaches the uterus (16 cells, called a morula).
Cells are totipotent (capable of differentiating into all cell types).
Morula
continues dividing, nourished by egg cytoplasm and "uterine milk."
Formation of Blastocyst
100 cells
: Form a blastocyst with:
Embryoblast
: Inner cell mass, becomes the embryo.
Trophoblast
: Outer shell, nourishes the embryo, becomes chorion (part of placenta).
Trophoblast secretes enzyme to hatch blastocyst for implantation.
Implantation
At the end of the first week, the blastocyst attaches to the endometrium.
Syncytiotrophoblast
forms, growing into the endometrium for nutrition.
Secretes
Human Chorionic Gonadotropin (HCG)
to maintain progesterone production by corpus luteum.
Formation of the Embryonic Disc (Week 2)
Embryoblast forms a two-layered disc (hypoblast and epiblast).
Sets dorsal/ventral axis (epiblast is dorsal).
Formation of yolk sac and amnion:
Yolk Sac
: Provides nutrients and gas exchange, first site of blood cell production.
Amnion
: Protects embryo, allows movement.
Gastrulation (Week 3)
Transformation into 3 germ layers: endoderm, mesoderm, ectoderm.
Initiated by the primitive streak formation.
Determines cranial/caudal axis.
Cells migrate through the primitive streak:
First cells form endoderm.
Second cells form mesoderm.
Remaining cells form ectoderm.
Formation of Organs and Tissues
By end of embryonic period, primitive forms of all organ systems are present.
Yolk Sac
gives rise to allantois (primitive urinary bladder).
Amnion
surrounds embryo with protective amniotic fluid.
Embryonic Membranes
Yolk Sac
Amnion
Allantois
Chorion
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