Histogenesis

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Histogenesis is the formation of different tissues from undifferentiated cells.[1] These cells are constituents of three primary germ layers, the endoderm, mesoderm, and ectoderm. The science of the microscopic structures of the tissues formed within histogenesis is termed histology.

Germ layers[edit]

Gastrulation 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).

A germ layer is a collection of cells, formed during animal and mammalian embryogenesis. Germ layers are typically pronounced within vertebrate organisms; however, animals or mammals 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. Therefore, 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.

Endoderm[edit]

The endoderm is one of the germ to penes 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.

Mesoderm[edit]

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.

Ectoderm[edit]

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.

Production[edit]

The endoderm 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.

Germ Layer Category Product
Endoderm General[2] Gastrointestinal tract
Endodern General Respiratory tract
Endoderm General Endocrine glands and organs (liver and pancreas)
Mesoderm General Bones
Mesoderm General Most of the Circulatory system
Mesoderm General Connective tissues of the gut and integuments
Mesoderm General Excretory Tract
Mesoderm General Mesenchyme
Mesoderm General Mesothelium
Mesoderm General Muscles
Mesoderm General Peritoneum
Mesoderm General Reproductive System
Mesoderm General Urinary System
Mesoderm Vertebrate[3] Chordamesoderm
Mesoderm Vertebrate Paraxial mesoderm
Mesoderm Vertebrate Intermediate mesoderm
Mesoderm Vertebrate Lateral plate mesoderm
Ectoderm General Nervous system
Ectoderm General Outer part of integument
Ectoderm Vertebrate Skin (along with glands, hair, nails)
Ectoderm Vertebrate Epithelium of the mouth and nasal cavity
Ectoderm Vertebrate Lens and cornea of the eye
Ectoderm Vertebrate Melanocytes
Ectoderm Vertebrate Peripheral nervous system
Ectoderm Vertebrate Facial cartilage
Ectoderm Vertebrate Dentin (in teeth)
Ectoderm Vertebrate Brain (rhombencephalon, mesencephalon and prosencephalon)
Ectoderm Vertebrate Spinal cord and motor neurons
Ectoderm Vertebrate Retina
Ectoderm Vertebrate Posterior pituitary

See also[edit]

References[edit]

  1. ^ histogenesis definition - Dictionary - MSN Encarta. Archived from the original on 2009-10-31. 
  2. ^ The General category denotes that all or most of the animals containing this layer produce the adjacent product.
  3. ^ The Vertebrate category denotes that all or most of the vertebrates containing this layer produce the adjacent product.
  • Microsoft Corporation. Histogenesis (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.

External links[edit]