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Terms in this set (17)

-human eggs are quite small, storing little in the way of food reserves.
-Fertilization takes place in the oviduct
-at the end of cleavage, the embryo has more than 100 cells arranged around a central cavity and has reached the uterus, embryo is called the blastocyst
-clustered at one end of the blastocyst cavity is a group of cells called the inner cell mass
-cells of the very early blastocyst stage that are the source of embryonic stem cell lines
-embryo implantation is initiated by the trophoblast, the outer epithelium of the blastocyst. Enzymes secreted by the trophoblast during implantation break down molecules of the endometrium, the lining of the uterus, allowing invasion by the blastocyst
-the inner cell mass of the blastocyst forms a flat disc with an inner layer of cells, the epiblast and outer layer the hypoblast
-following implantation, the trophoblast continues to expand into the endometrium, and four new membranes appear
-extraembryonic membranes arise from the embryo
-implantation is completed, gastrulation begins. Some epiblast cells remain as ectoderm on the surface, while others move inward through a primitive streak and form mesoderm and endoderm
-by the end of gastrulation, the embryonic germ layers have formed
-cells of the invading trophoblast, the epiblast, and the adjacent endometrial tissue all contribute to the formation of the placenta
-the placenta mediates the exchange of nutrients, gases, and nitrogenous wastes between the developing embryo and the mother
-reorganization of the cytoskeleton is a major force in changing cell shape during development
-in neural tube formation, microtubules oriented from dorsal to ventral in a sheet of ectodermal cells help lengthen the cells along that axis. At the dorsal end of each cell is a bundle of actin filaments (microfilaments) oriented crosswise. The actin filaments contract, giving the cells a wedge shape that bends the ectoderm layer inward
-the cytoskeleton also directs a morphogenetic movement called convergent extension, a rearrangement that causes a sheet of cells to become narrower while it becomes longer
-The cells elongate, with their ends pointing in the direction they will move, and they then wedge between each other to form fewer columns of cells
-An example is the archenteron elongates in the sea urchin embryo
-In involution in the frog gastrula, convergent extension changes the gastrulation embryo from a spherical shape to the rounded rectangular shape
-the cytoskeleton is also used for cell migration
-During organogenesis in vertebrates, cells from the neural crest and from somites migrate to locations through the embryo. Cells 'crawl' by using cytoskeletal fibers to extend and retract cellular protrusions (this mobility is akin to amoeboid movement)
-transmembrane glycoproteins called cell adhesion molecules are involved in cell migration by promoting interaction between pairs of cells
-cell migration involves the extracellular matrix (ECM), the meshwork of secreted glycoproteins and other macromolecules lying outside the plasma membranes of cells
-ECM helps guide migration of individual cells and shape changes of cell sheets. Cells that line migration pathways regulate movement of migrating cells by secreting specific molecules into the ECM