1. Chapter 47 Animal Development

2. Embryonic development/fertilization u Preformation~ until 18th century; miniature infant in sperm or egg u At fertilization/conception: u Acrosomal reaction~ hydrolytic enzyme action on egg jelly coat…. u Fast block to polyspermy~ membrane depolarization prevents multiple fertilizations…. u Cortical reaction~ release of calcium causes hardening of egg outer layer and creates a... u Slow block to polyspermy and... u Egg activation~ increases metabolic activity; protein synthesis

3. The Fertilized Egg & Cleavage u Blastomeres ~ resultant cells of cleavage/mitosis u Yolk ~ nutrients stored in the egg u Vegetal pole ~ side of egg with high yolk concentration u Animal pole ~ side of egg with low yolk concentration u Morula~ solid ball of cells u Blastocoel ~fluid-filled cavity in morula u Blastula ~hollow ball stage of development

4. Gastrulation u Gastrula ~ 2 layered, cup-shaped embryonic stage u 3 Embryonic germ layers: u Ectoderm~ outer layer; epidermis; nervous system, etc. u Endoderm ~ inner layer; digestive tract and associated organs; respiratory, etc. u Mesoderm ~skeletal; muscular; excretory, etc. u Invagination ~ gastrula buckling process to create the... u Archenteron ~ primitive gut u Blastopore ~ open end of archenteron

5. Organogenesis: organ formation u Blastodisc ~ cap of cells on top of yolk u Primitive streak ~ invagination of blastodisc u Neural tube ~ beginning of spinal cord u Somites~ vertebrae and skeletal muscles u Neural crest ~ bones and muscles of skull

6. Amniote embryos u Extraembryonic membranes : yolk sac (support; circulatory function) amnion (fluid-filled sac; protection) chorion (placenta formation) u allantois (nitrogenous waste)