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Pharyngeal arch
The pharyngeal arches, also known as visceral arches, are transient structures seen in the embryonic development of humans and other vertebrates, that are recognisable precursors for many structures. In fish, the arches support the gills and are known as the branchial arches, or gill arches.
In the human embryo, the arches are first seen during the fourth week of development. They appear as a series of outpouchings of mesoderm on both sides of the developing pharynx. The vasculature of the pharyngeal arches are the aortic arches that arise from the aortic sac.
In humans and other vertebrates, the pharyngeal arches are derived from all three germ layers, (the primary layers of cells that form during embryonic development). Neural crest cells enter these arches where they contribute to features of the skull and facial skeleton such as bone and cartilage. The existence of pharyngeal structures before neural crest cells evolved is indicated by the existence of neural crest-independent mechanisms of pharyngeal arch development.
The first, most anterior pharyngeal arch (in mammals) gives rise to the mandible. The second arch becomes the hyoid and jaw support.
In fish, the other posterior arches contribute to the branchial skeleton, which support the gills; in tetrapods the anterior arches develop into components of the ear, tonsils, and thymus.
The genetic and developmental basis of pharyngeal arch development is well characterized. It has been shown that Hox genes and other developmental genes such as DLX are important for patterning the anterior/posterior and dorsal/ventral axes of the branchial arches. Some fish species have a second set of jaws in their throat, known as pharyngeal jaws, which develop using the same genetic pathways involved in oral jaw formation.
During embryonic development, a series of pharyngeal arch pairs form. These project forward from the back of the embryo toward the front of the face and neck. Each arch develops its own artery, nerve that controls a distinct muscle group, and skeletal tissue. The arches are numbered from 1 to 6, with 1 being the arch closest to the head of the embryo, and arch 5 existing only transiently.
These grow and join in the ventral midline. The first arch, as the first to form, separates the mouth pit or stomodeum from the pericardium. By differential growth the neck elongates and new arches form, so the pharynx has six arches ultimately.
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Pharyngeal arch
The pharyngeal arches, also known as visceral arches, are transient structures seen in the embryonic development of humans and other vertebrates, that are recognisable precursors for many structures. In fish, the arches support the gills and are known as the branchial arches, or gill arches.
In the human embryo, the arches are first seen during the fourth week of development. They appear as a series of outpouchings of mesoderm on both sides of the developing pharynx. The vasculature of the pharyngeal arches are the aortic arches that arise from the aortic sac.
In humans and other vertebrates, the pharyngeal arches are derived from all three germ layers, (the primary layers of cells that form during embryonic development). Neural crest cells enter these arches where they contribute to features of the skull and facial skeleton such as bone and cartilage. The existence of pharyngeal structures before neural crest cells evolved is indicated by the existence of neural crest-independent mechanisms of pharyngeal arch development.
The first, most anterior pharyngeal arch (in mammals) gives rise to the mandible. The second arch becomes the hyoid and jaw support.
In fish, the other posterior arches contribute to the branchial skeleton, which support the gills; in tetrapods the anterior arches develop into components of the ear, tonsils, and thymus.
The genetic and developmental basis of pharyngeal arch development is well characterized. It has been shown that Hox genes and other developmental genes such as DLX are important for patterning the anterior/posterior and dorsal/ventral axes of the branchial arches. Some fish species have a second set of jaws in their throat, known as pharyngeal jaws, which develop using the same genetic pathways involved in oral jaw formation.
During embryonic development, a series of pharyngeal arch pairs form. These project forward from the back of the embryo toward the front of the face and neck. Each arch develops its own artery, nerve that controls a distinct muscle group, and skeletal tissue. The arches are numbered from 1 to 6, with 1 being the arch closest to the head of the embryo, and arch 5 existing only transiently.
These grow and join in the ventral midline. The first arch, as the first to form, separates the mouth pit or stomodeum from the pericardium. By differential growth the neck elongates and new arches form, so the pharynx has six arches ultimately.