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mitosis cleavage mitosis cleavage solid ball of cells Morula is Latin for mulberry result of early cleavages takes about 96 hours hollow ball of cells day 6 of development On top is the inner cell mass where the embryonic stem cells are •lots of telomerase; “immortal” Once the blastula reaches several hundred cells, the embryo indents and becomes 3-layered (germ layers) endoderm- inner layer ectoderm- outer mesoderm- middle week 7-8 laser clip 1 laser clip 2 •the changing of unspecialized cells into 210 different types of cells, tissues, organs •occurs during gastrula phase; when the cells become “different” •endoderm becomes liver, pancreas, lining of organs •mesoderm becomes muscles, skeleton, circ. Sys. •ectoderm becomes skin, nervous sys., hair, nails Increase in size and/or # of cells embryonic devel clip differentiation link fertilization cleavage/mitosis cleavage/mitosis differentiation/ gastrulation differentiation growth Stem cells- undifferentiated cells that have the ability to become specialized cells *totipotent a. Adult stem cells •Some adult tissues contain stem cells: brain, bone marrow, blood, vessels, muscle, skin, liver •these cells give rise to “like” cells (liver liver) •hoped to be used to treat Parkinson’s, diabetes, etc. b. Embryonic stem cells •grown from in-vitro fertilized eggs (controversial) •taken from the 4-6 day old blastula •toti/pluripotent- Can become (potentially) ANY type of cell. They can truly differentiate downside: abundance of telomerase may lead to….. cancer also destroys the embryo cord blood…stem cells internal internally uterus yolk the mother/placenta internally yolk combination of maternal & embryonic tissues materials exchanged by diffusion blood supplies don’t mix contains blood vessels attaches embryo to placenta yolk externally pouch