Edit Page
Source Editor

Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.

The edit can be undone. Please check the comparison below to verify that this is what you want to do, and then save the changes below to finish undoing the edit.

This page supports semantic in-text annotations (e.g. "[[Is specified as::World Heritage Site]]") to build structured and queryable content provided by Semantic MediaWiki. For a comprehensive description on how to use annotations or the #ask parser function, please have a look at the getting started, in-text annotation, or inline queries help pages.

Latest revision Your text
Line 1: Line 1:
 
{{BioPsy}}
 
{{BioPsy}}
  +
 
A '''germ layer''' is a collection of [[cell (biology)|cell]]s, formed during animal [[embryogenesis]]. Germ layers are only really pronounced in the [[vertebrate]]s. However, all [[animal]]s more complex than [[sponge]]s ([[eumetazoa]]ns and [[wikispecies:agnotozoa|agnotozoans]]) produce two or three '''primary tissue layers''' (sometimes called primary germ layers). Animals with [[symmetry (biology)#Radial symmetry|radial symmetry]], like [[cnidaria]]ns, produce two called '''ectoderm''' and '''endoderm'''. Animals with [[symmetry (biology)#Bilateral symmetry|bilateral symmetry]] produce a third layer in-between called '''mesoderm'''. Germ layers will eventually give rise to all of an animal’s [[biological tissue|tissues]] and [[organ (anatomy)|organ]]s through a process called '''organogenesis'''.
 
A '''germ layer''' is a collection of [[cell (biology)|cell]]s, formed during animal [[embryogenesis]]. Germ layers are only really pronounced in the [[vertebrate]]s. However, all [[animal]]s more complex than [[sponge]]s ([[eumetazoa]]ns and [[wikispecies:agnotozoa|agnotozoans]]) produce two or three '''primary tissue layers''' (sometimes called primary germ layers). Animals with [[symmetry (biology)#Radial symmetry|radial symmetry]], like [[cnidaria]]ns, produce two called '''ectoderm''' and '''endoderm'''. Animals with [[symmetry (biology)#Bilateral symmetry|bilateral symmetry]] produce a third layer in-between called '''mesoderm'''. Germ layers will eventually give rise to all of an animal’s [[biological tissue|tissues]] and [[organ (anatomy)|organ]]s through a process called '''organogenesis'''.
  +
 
[[Image:cell differentiation.gif|right|thumb|Organs derived from each germ layer. Image from [http://www.ncbi.nih.gov/About/primer/genetics_cell.html NCBI].]]
   
 
==Germ layer==
 
==Germ layer==
 
[[Image:Gastrulation.png|thumb|300px|'''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).]]
  +
 
[[Caspar Friedrich Wolff]] observed organization of the early embryo in leaf-like layers. Later, [[Heinz Christian Pander]] discovered germ layers while studying chick embryos.
 
[[Caspar Friedrich Wolff]] observed organization of the early embryo in leaf-like layers. Later, [[Heinz Christian Pander]] discovered germ layers while studying chick embryos.
  +
 
According to the number of layers produced, animals are classified as [[diploblastic]] (two layers) or [[triploblastic]] (three layers). All animals, except for those in the branch [[radiata]], are triploblastic.
 
According to the number of layers produced, animals are classified as [[diploblastic]] (two layers) or [[triploblastic]] (three layers). All animals, except for those in the branch [[radiata]], are triploblastic.
 
   
 
===Development===
 
===Development===
 
[[fertilisation|Fertilization]] leads to the formation of a [[zygote]]. During the next stage, [[cleavage (embryo)|cleavage]], [[mitosis|mitotic]] cell divisions transform the zygote into a tiny ball of cells called a [[blastula]]. This early embryonic form undergoes a massive reorganization called [[gastrulation]] forming a [[gastrula]] with either two or three layers (the germ layers). In all [[vertebrate]]s, these are the forerunners of all adult tissues and organs.
 
[[fertilisation|Fertilization]] leads to the formation of a [[zygote]]. During the next stage, [[cleavage (embryo)|cleavage]], [[mitosis|mitotic]] cell divisions transform the zygote into a tiny ball of cells called a [[blastula]]. This early embryonic form undergoes a massive reorganization called [[gastrulation]] forming a [[gastrula]] with either two or three layers (the germ layers). In all [[vertebrate]]s, these are the forerunners of all adult tissues and organs.
  +
 
The appearance of the [[archenteron]] marks the onset of gastrulation.
 
The appearance of the [[archenteron]] marks the onset of gastrulation.
  +
[[Image:Gastrulation.png|thumb|300px|'''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).]]
 
 
==Ectoderm==
 
==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.
 
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.
Line 17: Line 23:
 
*[[Nervous system]]
 
*[[Nervous system]]
 
*Outer part of [[integumentary system|integument]]
 
*Outer part of [[integumentary system|integument]]
[[Image:cell differentiation.gif|right|thumb|Organs derived from each germ layer. Image from [http://www.ncbi.nih.gov/About/primer/genetics_cell.html NCBI].]]
 
   
 
===What forms from it (vertebrates)?===
 
===What forms from it (vertebrates)?===
 
In [[vertebrate]]s, the ectoderm has three parts: external ectoderm, the [[neural crest]], and neural tube.
 
In [[vertebrate]]s, the ectoderm has three parts: external ectoderm, the [[neural crest]], and neural tube.
   
*[[External Ectoderm]]
+
*External Ectoderm
 
**[[skin]] (along with [[glands]], [[hair]], [[nails]])
 
**[[skin]] (along with [[glands]], [[hair]], [[nails]])
 
**[[epithelium]] of the [[mouth]] and [[nasal cavity]]
 
**[[epithelium]] of the [[mouth]] and [[nasal cavity]]
 
**[[lens (vision)|lens]] and [[cornea]] of the [[eye]]
 
**[[lens (vision)|lens]] and [[cornea]] of the [[eye]]
   
*[[Neural Crest]]
+
*Neural Crest
 
**[[melanocytes]]
 
**[[melanocytes]]
 
**[[peripheral nervous system]]
 
**[[peripheral nervous system]]
Line 33: Line 38:
 
**[[dentin]] (in teeth)
 
**[[dentin]] (in teeth)
   
*[[Neural Tube]]
+
*Neural Tube
 
**[[brain]] ([[rhombencephalon]], [[mesencephalon]] and [[prosencephalon]])
 
**[[brain]] ([[rhombencephalon]], [[mesencephalon]] and [[prosencephalon]])
 
**[[spinal cord]] and [[motor neuron]]s
 
**[[spinal cord]] and [[motor neuron]]s
Line 40: Line 45:
   
 
==Endoderm==
 
==Endoderm==
Cells migrating inward along the [[archenteron]] form the inner layer of the gastrula, which develops into the [[endoderm]].
+
Cells migrating inward along the [[archenteron]] form the inner layer of the gastrula, which develops into the endoderm.
   
 
===What forms from it?===
 
===What forms from it?===
Line 48: Line 53:
   
 
==Mesoderm==
 
==Mesoderm==
[[Mesoderm]] forms in the embryos of animals more complex than cnidarians. Some of the cells migrating inward to form the endoderm form an additional layer between the other two.
+
Mesoderm forms in the embryos of animals more complex than cnidarians. Some of the cells migrating inward to form the endoderm form an additional layer between the other two.
   
 
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|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.
 
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|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.
   
 
===Categorizing Animals===
 
===Categorizing Animals===
Not all [[triploblastic]] animals have a coelom, like [[flatworm]]s, the simplest animals with organs that form from three tissue layers. Three different configurations of mesoderm in relation to ectoderm form a method of categorizing animals.
+
Not all triploblastic animals have a coelom, like [[flatworm]]s, the simplest animals with organs that form from three tissue layers. Three different configurations of mesoderm in relation to ectoderm form a method of categorizing animals.
   
 
*'''Acoelomates'''
 
*'''Acoelomates'''
Line 66: Line 71:
   
 
===What forms from it (general)?===
 
===What forms from it (general)?===
Note: Not all [[triploblasts]] produce all of the items listed.
+
Note: Not all triploblasts produce all of the items listed.
 
*[[skeletal system|Bones]]
 
*[[skeletal system|Bones]]
 
*most of the [[Circulatory system]]
 
*most of the [[Circulatory system]]
Line 81: Line 86:
 
In addition to the general list, the mesoderm of a developing vertebrate differentiates into the following:
 
In addition to the general list, the mesoderm of a developing vertebrate differentiates into the following:
   
*[[Chordamesoderm]]
+
*Chordamesoderm
 
**lies along the central axis, under the neural tube
 
**lies along the central axis, under the neural tube
 
**gives rise to the notochordal process which later becomes the [[notochord]]
 
**gives rise to the notochordal process which later becomes the [[notochord]]
   
*[[Paraxial Mesoderm]]
+
*Paraxial Mesoderm
 
**at the sides of the neural tube
 
**at the sides of the neural tube
 
**gives rise to the [[somite]]s and head mesoderm.
 
**gives rise to the [[somite]]s and head mesoderm.
Line 91: Line 96:
 
***head mesoderm will develop into facial muscle and cartilage
 
***head mesoderm will develop into facial muscle and cartilage
   
*[[Intermediate Mesoderm]]
+
*Intermediate Mesoderm
 
**located between the paraxial mesoderm and the lateral plate
 
**located between the paraxial mesoderm and the lateral plate
 
**develops into the part of the urogenital system ([[kidney]]s and [[gonad]]s)
 
**develops into the part of the urogenital system ([[kidney]]s and [[gonad]]s)
   
*[[Lateral Plate Mesoderm]]
+
*Lateral Plate Mesoderm
 
**found at the periphery of the embryo
 
**found at the periphery of the embryo
 
**will split into two layers, the somatic layer/mesoderm and the splanchnic layer/mesoderm
 
**will split into two layers, the somatic layer/mesoderm and the splanchnic layer/mesoderm

Please note that all contributions to the Psychology Wiki are considered to be released under the CC-BY-SA

Cancel Editing help (opens in new window)