development and growth. embryology so…meiosis gives us gametes which unite through fertilization...
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Embryology
So…meiosis gives us gametes which unite through fertilization to form a fertilized zygote. Now what?
9 months later….
A baby is born with a complete body structure, both inside and out. How do we get there?
We must look at the early stages of
embryology (study of dev. embryos) as these early stages set up the body for the rest of the pregnancy
Definitions Development- a series of events that
give rise to a full grown organism Embryo- a multicellular organism in
the early stages of development Differentiation- a series of changes that
transforms unspecialized embryonic cells into specialized cells, tissues, and organs.
Cleavage- series of cell divisions by the zygote
After fertilization….
Zygote begins a series of cell divisions called cleavage
Cleavage occurs every 20 hours. To produce more cells that decrease in size until all cells are the size they will be of the adult.
Stage 3: Embryo Development
Gastrula- cells on one side of the blastula move inward and form a two layered embryo
opening is created- blastopore
Embryo Development
The 2nd week of human development Gastrulation– early in development, a gut is created
through an intucking of cells from the exterior of the embryo into the interior
– It results in 3 basic germ layers• Ectoderm• Mesoderm• Endoderm
Embryo Development
The endoderm differentiates into– digestive tract– lungs– bladder
The mesoderm differentiates into– skeleton– skeletal muscle– connective tissue
Embryo Development
By the 4th week of human development
–Neurulation (nervous system) is underway
–Gastrulation is complete
Embryo Development
By the 5th week of human development
–Limb buds are present
–Organs start to form
Fetal Development
By the 10th week of human development
–Intestines are located in the abdomen
–Fingernail development
Fetal Development
By the 15th week of human development
–Fetus is very recognizable
–While internal organs continue to grow and mature, the external appearance is very human-like
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