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Animal Development. Chapter 47. Post-fertilization. After fertilization, embryology occurs Embryology is the development of the zygote Focus on the development of mammalian embryos.

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Animal development

Animal Development

Chapter 47

Post fertilization

  • After fertilization, embryology occurs

  • Embryology is the development of the zygote

  • Focus on the development of mammalian embryos

Acrosomal Reaction – the acrosome on the sperm secretes hydrolytic enzymes to digest the egg’s jelly coat.

Acrosomal process – actin filaments that protrude from acrosome & binds to membrane receptors on the egg

Notes on fertilization
Notes on Fertilization

  • After the acrosomal process binds to membrane receptors, the sperm & egg membranes fuse

  • Depolarization of the egg membrane occurs preventing other sperm from binding to the egg

    • Depolarization is due to ion channels opening in the egg membrane, so Na+ ions flow into the egg

    • Depolarization prevents Polyspermy – more than 1 sperm binding to an egg

  • Is polyspermy bad?

Notes on fertilization page 2
Notes on Fertilization (page 2)

  • Cortical reaction

    • Fusion of gametes results in release of Ca2+ ions from the ER into the space between the jelly coat and plasma membrane

      • Swelling of the perivitelline space

      • Hardening of the vitelline layer

      • Removal of sperm-binding receptors on egg membrane

      • Collectively the above are called the fertilization envelope

    • Ca2+ ion release also causes activation of the egg/zygote to undergo an ontogenic process

Ectoderm – Skin, teeth, Nervous system

Mesoderm – Skeletal, Muscular, Circulatory, Reproductive Systems (Blood, bones, and muscles)

Endoderm – Epithelial linings of the digestive, respiratory, & excretory tract. Liver & Pancreas as well

Continuing development
Continuing Development

  • Organogenesis

    • Development of the 3 germ layers into rudimentary organs

    • Notochord – rigid dorsal rod (cartilage or bone)

      • Develops from mesoderm

    • Neural plate – will become brain & spinal cord

      • Develops from ectoderm

    • Neurulation

      • Process of forming dorsal hollow nerve chord

  • Blastocyst – mammalian version of blastula

  • Inner cell mass – group of cells that develops into the embryo

    • Source of embryonic stem cell lines

  • Trophpblast – outer epithelium of the blastocyst, becomes the fetal portion of placenta

Pattern of development
Pattern of Development

  • Development is governed by a combination of cytoplasmic determinants & inductive cell signals

  • Cytoplasmic determinants

    • Chemical signals such as mRNA & transcription factors that were distributed unevenly during cleavage

  • Induction

    • Interaction among cells that influence their fate

    • Causes changes in gene expression among cells

Totipotent cells
Totipotent Cells

  • Cells that are capable of developing into ANY possible cell type

    • As long as it possesses the requisite genetics, it can become muscular, nervous, epithelial, etc.

    • If you have a totipotent cell, you can literally grow another organism, and you can grow as many as you would like

  • Totipotent cells exist until the 16-cell stage of cleavage

  • After that, they are pluripotent – can become any of the 3 germ layers, but cannot develop into a new being

Ips cells
iPS Cells

  • iPS – Induced pluripotent stem cells

  • Take an adult (fully differentiated) cell, modify the signaling being received, thus altering the genetic expression of certain “induction” genes

  • Future of medicine?