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Download Fertilization Notes #2
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FERTILIZATION & DEVELOPMENT--#2 Prenatal Development GESTATION • Definition: period of time between fertilization and birth • Typically lasts 38 weeks or 9 months STAGES OF DEVELOPMENT • Fertilization of the egg occurs forming a structure called a zygote • After the zygote divides into two cells it is called an embryo • After 3 days, mitotic divisions occur resulting in a 16 cell structure, then eventually a structure of 32 cells AFTER 5 DAYS • a solid ball of cells, or morula, develops and the embryo attaches to the uterus CONTINUED MITOSIS • division continues until the center of the ball becomes hollow forming the blastula GASTRULATION • The blastula pushes inward on one side, resulting in the formation of a 2layered gastrula the inner layer is called the endoderm the outer layer is called the ectoderm FROM 2 to 3 LAYERS • Eventually, a third cell layer, or mesoderm will form Diagram WHAT NEXT?? • The embryonic cells specialize to perform the various tasks of particular tissues throughout the body, a process called differentiation The 3 cell layers will form the following: 1. Ectoderm--outer skin, nervous system 2. Endoderm--lining of digestive tract, respiratory tract, portions of liver and pancreas 3. Mesoderm--muscles, gonads, and the circulatory, skeletal, excretory systems DIAGRAM Diagram
