histogenesis

File:Gastrulation.png of a diploblast: The formation of germ layers from a (1) blastula to a (2) gastrula. Some of the ectoderm cells (orange) move inward forming the endoderm (red).]]

{{Main|Germ layer}}

A germ layer is a collection of cells formed during animal embryogenesis. Germ layers are typically pronounced within vertebrate organisms; however, animals more complex than sponges (eumetazoans and agnotozoans) produce two or three primary tissue layers. Animals with radial symmetry, such as cnidarians, produce two layers, called the ectoderm and endoderm. They are diploblastic. Animals with bilateral symmetry produce a third layer in-between called mesoderm, making them triploblastic. Germ layers will eventually give rise to all of an animal's or mammal's tissues and organs through a process called organogenesis.

{{Main|Endoderm}}

The endoderm is one of the germ layers formed during animal embryogenesis. Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm. Initially, the endoderm consists of flattened cells, which subsequently become columnar...

{{Main|Mesoderm}}

The mesoderm germ layer forms in the embryos of animals and mammals more complex than cnidarians, making them triploblastic. During gastrulation, some of the cells migrating inward to form the endoderm form an additional layer between the endoderm and the ectoderm. A theory suggests that this key innovation evolved hundreds of millions of years ago and led to the evolution of nearly all large, complex animals. The formation of a mesoderm led to the formation of a coelom. Organs formed inside a coelom can freely move, grow, and develop independently of the body wall while fluid cushions and protects them from shocks.

{{Main|Ectoderm}}

The ectoderm is the start of a tissue that covers the body surfaces. It emerges first and forms from the outermost of the germ layers.

File:Germ layers.jpg produces tissue within the lungs, thyroid, and pancreas. The mesoderm aids in the production of cardiac muscle, skeletal muscle, smooth muscle, tissues within the kidneys, and red blood cells. The ectoderm produces tissues within the epidermis and aids in the formation of neurons within the brain, and melanocytes.]]

The proceeding graph represents the products produced by the three germ layers.

• Histology
• List of human cell types derived from the germ layers

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• Microsoft Corporation. [http://www.encarta.msn.com/dictionary_/Histogenesis.html Histogenesis] {{Webarchive|url=https://web.archive.org/web/20090328200143/http://encarta.msn.com/dictionary_/histogenesis.html |date=2009-03-28 }} ([https://web.archive.org/web/20090328200143/http://encarta.msn.com/dictionary_/histogenesis.html Archived] 2009-10-31). Encarta World English Dictionary (North American Edition). URL accessed on 14 May 2005.
• Evers, Christine A., Lisa Starr. Biology:Concepts and Applications. 6th ed. United States:Thomson, 2006. {{ISBN|978-0-534-46224-6}}.

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{{Wiktionary|histogenesis}}

• {{in lang|en}} [http://www.uoguelph.ca/zoology/devobio/splab7/index.htm Derivatives of the Ectoderm]
• {{in lang|en}} [http://www.uoguelph.ca/zoology/devobio/splab8/index.htm Derivatives of the Endoderm and Mesoderm]

{{Embryology}}

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Category:Developmental biology

Category:Embryology

Category:Histology