Gastrulation is the process that occurs during the third week of embryonic development and includes transformation of embryonic disc with epiblast and hypoblast into a three layered embryonic disc made up of ectoderm, mesoderm and endoderm. These are the three primary germ layers and give rise to various tissues and body organs.
Endoderm of the embryo give rise to epithelial lining of gastrointestinal tract (except the buccal cavity), respiratory tracts and other organs such as gallbladder, liver,etc. Mesoderm forms connective tissues such as bones as well as muscles and peritoneum. All the tissues of nervous system and epidermis of skin are derived from ectoderm.
Centrioles are only found in animal cells and they help during cell division. They organize the spindle fibers that help elongate the cell and separate the chromosomes.
