Study Booklet (work In Progress)

Human Embryo Development Study Guide

Solomon Berg Martin

Gametogenesis • 1

Overview 1. Gametogenesis

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2. Fertilization

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4. Blastulation

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5. Gastrulation

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6. Organogenesis

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7. Development

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Gametogenesis is the process of gamete formation. The two types of gametogensis in humans are spermatogenesis and oogenesis. Spermatogenesis

How to Use This Guide

Spermatogenesis is the process of sperm cell production. In humans, it takes place in paired male gonads, called testes. Within the testes, spermatogenesis takes place within the seminiferous tubules.

This study guide is not meant to replace a general biology textbook. Instead, this booklet serves as supplementary study material. It is designed for an abbreviated, but comprehensive

Oogenesis

Oogenesis is the process of ovum production that begins in the ovaries. Oogonia increase in size and become primary oocytes. The primary oocyte undergoes a series of meiotic divisions to become an ovum.

Spermatogonium (2n) Mitosis

understanding of human embryology. In this booklet, you will find images of the various stages in human embryo

Oogonium (2n)

Primary spermatocyte (2n) Meiosis I Secondary spermatocyte (n) Meiosis II Spermatid (n)

development. The text will provide a description of the most important aspects of each stage of development.

Sperm (n)

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Mitosis Primary oocyte (2n) Meiosis

Polar body (degenerates)

Secondary oocyte (n)

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Fertilization • 2

Gastrulation • 3

After cleaveage, a series of rapid mitotic division with no period of growth during each cycle, gastrulation takes place. During gastrulation, the embryo begins to approximate its body plan in germ layers.

Fertilization is the process by which the motile sperm fuses with the immotile ovum to produce a zygote, or fertilized egg. Fertilzation involves four events, which may or may not occur simultaneously. Contact and Recognition

Ectoderm

When sperm comes in contact with a ovum, the sperm undergoes an acrosome reaction. The acrosome releases enzymes to digest through the eggs jelly coat. Compatible sperm and egg will secrete species specific bindin.

The ectoderm is the outermost germ layer. This germ layer develops into the nervous system and sense organs. The epidermis of the skin and the associated structures are also formed from the ectoderm. The pituitary gland is also formed from this germ layer.

Sperm Entry

Enzymes from the sperm acrosome partially dissolve a bit of the vitelline envelope. In this area, microvilli on the plasma membrane of the egg elongate to surround the sperm head. The plasma membranes of the egg and sperm fuse to form a fertilization cone that draws the sperm into the egg.

Mesoderm

The mesoderm is the germ layer from which most tissues arise. Mesodermal structures include the notochord, skeleton, muscles, and the dermis of the skin. The circulatory, excretory, and reproductive systems also arise from the mesoderm.

Egg Activation

Release of calcium ions into the egg cytoplasm triggers the activation program, a series of metabolic changes within the egg. Certain enzymes and proteins become active and a burst of protein synthesis occurs. Lastly, the egg nucleus completes meiosis and forms the female pronucleus.

Endoderm

The endoderm is the innermost germ layer of the gastrula. This germ layer gives rise to the lining of the structures that develop from it. For example, the lining of the digestive tract and the lining of the respiratory system develop from the endoderm.

Pronuclei Fusion

The sperm is guided to the egg nucleus by a system of microtubules. The sperm nucleus swell and forms the male pronucleus. The haploid male and female pronuclei fuse to form the diploid nucleus of the zygote.

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From top: Nerves, muscle, GI lining

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Organogenesis • 4

Development • 5

Organogenesis is organ formation, in which the cells of the three germ layers continue the processes of pattern formation that lead to the formation of specific structures. Neurulation

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