DAT Developmental Biology
embryology - ANS study of the development of a unicellular zygote into a complete,
multicellular organism
early developmental stages - ANS fertilization, Cleavage
cleavage - ANS these divisions lead to an increase in cell number without a corresponding
growth in cell protoplasm. Thus cleavage results in progressively smaller cells with an
increasing ratio of nuclei to cytoplasm. it increase surface area- improving gas and nutrient
exchange
First complete cleavage of a zygote occurs approx. _____ the second ____ the third ___ - ANS
32 hours after fertilization the second occurs after 60 hours and the third is 72 hours at which
eight celled embryo reaches the uterus
morula - ANS solid all of embryonic cells
blastulation begins when - ANS morula develops a fluid- filled cavity call blastocoel, which by
the fourth day becomes a hollow sphere of cells blastula
blastula - ANS hollow sphere of cells, at this stage embryo that implants in the uterus.
emergency contraception - ANS works partially by inhibiting implantation of the blastula in the
uterus which is why it is most effective if taken within 72 hours of time of potential fertilization
normal pregnancy - ANS implant in the uterus, if outside of uterus most of the time it aborts
ectopic pregnancy - ANS embryo implant outside the uterus
Gastrulation - ANS after week 2 the embryo is fully implanted in the uterus and cell migration
transforms the single cell layer of the blastula into a three layer structure called a gastrula.
ectoderm - ANS integumentary system- epidermis, hair, nail, epithelium of nose, mouth- lens of
eyes, the retina, the nervous system.
endoderm - ANS epithelial lining of digestive tract and respiratory tracts and parts of liver,
pancreas, thyroid, and bladder lining
mesoderm - ANS musculoskeletal system, circulatory system, excretory system, gonads,
connective tissue throughout body, and portion of digestive and respiratory organs
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