Stomodeum
Encyclopedia
The stomodeum, also called stomatodeum or stomatodaeum, is a depression between the brain
and the pericardium
in an embryo
, and is the precursor of the mouth
and the anterior lobe of the pituitary gland
.
, and is separated from the anterior end of the fore-gut by the buccopharyngeal membrane.
This membrane is devoid of mesoderm
, being formed by the apposition of the stomodeal ectoderm with the fore-gut endoderm; at the end of the third week it disappears, and thus a communication is established between the mouth and the future pharynx
.
By the growth of the head end of the embryo
, and the formation of the cephalic flexure
, the pericardial area and the buccopharyngeal membrane
come to lie on the ventral surface of the embryo
.
With the further expansion of the brain
, and the forward bulging of the pericardium
, the buccopharyngeal membrane
is depressed between these two prominences. This depression constitutes the stomodeum.
No trace of the membrane is found in the adult; and the communication just mentioned must not be confused with the permanent isthmus faucium.
The lips
, teeth, and gums are formed from the walls of the stomodeum, but the tongue
is developed in the floor of the pharynx.
Other sources (much probably) suggest it is from the Greek stoma- and odaios, "a way"
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
and the pericardium
Pericardium
The pericardium is a double-walled sac that contains the heart and the roots of the great vessels.-Layers:...
in an embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
, and is the precursor of the mouth
Mouth
The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....
and the anterior lobe of the pituitary gland
Pituitary gland
In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
.
Structure
The stomodeum is lined by ectodermEctoderm
The "ectoderm" is one of the three primary germ cell layers in the very early embryo. The other two layers are the mesoderm and endoderm , with the ectoderm as the most exterior layer...
, and is separated from the anterior end of the fore-gut by the buccopharyngeal membrane.
This membrane is devoid of mesoderm
Mesoderm
In all bilaterian animals, the mesoderm is one of the three primary germ cell layers in the very early embryo. The other two layers are the ectoderm and endoderm , with the mesoderm as the middle layer between them.The mesoderm forms mesenchyme , mesothelium, non-epithelial blood corpuscles and...
, being formed by the apposition of the stomodeal ectoderm with the fore-gut endoderm; at the end of the third week it disappears, and thus a communication is established between the mouth and the future pharynx
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
.
Development
The mouth is developed partly from the stomodeum, and partly from the floor of the anterior portion of the fore-gut.By the growth of the head end of the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
, and the formation of the cephalic flexure
Cephalic flexure
The mesencephalic flexure or cephalic flexure is the first flexure, or bend, of the embryonic brain; it appears in the region of the mid-brain...
, the pericardial area and the buccopharyngeal membrane
Buccopharyngeal membrane
The region where the crescentic masses of the ectoderm and endoderm come into direct contact with each other constitutes a thin membrane, the buccopharyngeal membrane , which forms a septum between the primitive mouth and pharynx...
come to lie on the ventral surface of the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
.
With the further expansion of the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
, and the forward bulging of the pericardium
Pericardium
The pericardium is a double-walled sac that contains the heart and the roots of the great vessels.-Layers:...
, the buccopharyngeal membrane
Buccopharyngeal membrane
The region where the crescentic masses of the ectoderm and endoderm come into direct contact with each other constitutes a thin membrane, the buccopharyngeal membrane , which forms a septum between the primitive mouth and pharynx...
is depressed between these two prominences. This depression constitutes the stomodeum.
No trace of the membrane is found in the adult; and the communication just mentioned must not be confused with the permanent isthmus faucium.
The lips
Lip
Lips are a visible body part at the mouth of humans and many animals. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech...
, teeth, and gums are formed from the walls of the stomodeum, but the tongue
Tongue
The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...
is developed in the floor of the pharynx.
Etymology
From the Greek stoma ("mouth or jaw") and Latin Deum ("God") for "mouth of God", indicative of its large size in development.Other sources (much probably) suggest it is from the Greek stoma- and odaios, "a way"
