Lecture 20, Ch. 47

Lecture #20

Date ________

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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

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Yolk~ nutrients stored in the egg Vegetal pole~ side of egg with high yolk concentration

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Animal pole ~ side of egg with low yolk concentration

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Morula~solid ball of cells Blastocoel~fluid-filled cavity in morula

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Blastula~hollow ball stage of development

Cleavage

QuickTimeª and a Cinepak decompressor are needed to see this picture.

Gastrulation ◆

Gastrula~ 2 layered, cup-shaped embryonic stage

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3 Embryonic germ layers:

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Ectoderm~ outer layer; epidermis; nervous system, etc. Endoderm~ inner layer; digestive tract and

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associated organs; respiratory, etc. ◆

Mesoderm~skeletal; muscular; excretory, etc.

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Invagination~ gastrula buckling process to create the...

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Archenteron~ primitive gut Blastopore~ open end of archenteron

Organogenesis: organ formation ◆

Blastodisc~ cap of cells on top of yolk

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Primitive streak~ invagination of blastodisc

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Neural tube~ beginning of spinal cord

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Somites~

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Neural crest~ bones and

vertebrae and skeletal muscles muscles of skull

Amniote embryos ◆

Extraembryonic membranes: •yolk sac •amnion

(support; circulatory function) (fluid-filled sac; protection)

•chorion •allantois

(placenta formation) (nitrogenous waste)