Histogenesis is the formation of different tissues from undifferentiated cells.
These cells are constituents of three primary
, 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,
more complex than
sea sponge (
and ) produce two or three primary tissue layers. Animals with radial symmetry, such as
, 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
of
and
more complex than
, 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
body cavity. 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
.
Production
The proceeding graph represents the products produced by the three germ layers.
See also
-
Histology
-
List of human cell types derived from the germ layers
Further reading
-
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. .
External links
