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Lecture Unit 1

Prenatal period First 38 weeks of human development. Scientific weeks.
Pre-embryonic period Weeks 1-2
Embryonic period Weeks 3-8
Fetal period Weeks 9-38
Fertilization When sperm enters egg. Occurs in the uterine tube.
Zygote When genetic material mixes
Cleavage Cell division
Morula 16 cell stage
Blastocyst Composed of 2 parts: Trophoblast-becomes the fetal half of placenta & Embryoblast, Aka: inner cell mass (ICM)-becomes the embryo.
Trophoblast 2 layers: Cytotrophoblast: inner layer & Synctiotrophoblast: Outer layer. Layers form the Chorion which creates fetal part of placenta.
The Bilaminar disc ICM divides. 2 sheets of cells: epiblast (top) & hypoblast (bottom). Epiblast forms embryo & Amnion. Hypolast forms yolk sac.
Embryonic period: Formation of Three germ layers Embryonic period. Primitive streak appears on dorsal surface of epiblast. Gastrulation. Cells that invaginate form mesoderm and endoderm. Remaining cells: ectoderm. Hypoblast regresses.
Gastrulation epiblast cells invaginate (move) through the primitive streak towards the hypoblast.
Body folding Transverse: L & R sides of embyo curve toward midline. Forms cylindrical trunk w/ ectoderm covering exterior. Cephalocaudal: In head and tail regions. Creates future head and butt
Ectoderm derivatives Skin and nervous tissue
Endoderm derivatives Digestive and respiratory systems
Mesoderm derivatives Muscle, tissue, heart, kidneys, reproductive organs
Neurulation The notochord, a tube of mesoderm, forms parallel & deep to primative streak. It stimulates ectoderm to form the neural tube which becomes brain & spinal cord.
Induction One structure influencing another structure to change form
Organogenesis Organ development follows gastrulation and body folding. Most organ systems have developed by week 8. Embryo 1" long.
Fetal Period Growth and maturation of organs
Birth defects 3/100 in US have serious structural birth defect. Causes of 50% of birth defects are unknown.
Teratogen Anything that causes a birth defect. Embryo particularly sensitive during embryonic period.
Fetal Alcohol Syndrome (FAS) Preventable. Growth retardation, heart defects, microcephally (small brain), leading cause of mental retardation.
Accutane 25% of bables born to mothers taking Accutane have serious birth defects and 50% are mentally disabled.
Created by: punkaloo