CHAPTER 47 Animal Development

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

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

Cleavage

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

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

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