Histogenesis

Histogenesis is the formation of different tissues from undifferentiated cells. 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

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.

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...

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.

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.

Production

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

Germ Layer Category Product Endoderm GeneralThe General category denotes that all or most of the animals containing this layer produce the adjacent product. Gastrointestinal tract Endodern General Respiratory tract Endoderm General Endocrine glands and organs (liver and pancreas) Mesoderm VertebrateThe Vertebrate category denotes that all or most of the vertebrates containing this layer produce the adjacent product. Bones and most cartilage 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 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 & prosencephalon) Ectoderm Vertebrate Spinal cord and motor neurons Ectoderm Vertebrate Retina Ectoderm Vertebrate Posterior pituitary

Histogenesis

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