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From fish gill arches to human facial bones: the amazing evolution of pharyngeal arch development!
Pharyngeal arches are transient structures that appear during the embryonic development of vertebrates. These structures have evolved to form a variety of important organs and tissues in many organisms. In fish, the pharyngeal arches support the gills, so they are called branchial arches or branching arches. In human embryonic development, the formation of the pharyngeal arches is equally important. They are first observed in the fourth week of embryonic development. .
During development, the importance of the pharyngeal arches is obvious, as they are the precursors of many structures.
The development of the pharyngeal arches begins on both sides of the embryo and is formed by the bulging of the mesoderm. These longitudinal structures play an important role in the development of organisms, such as the formation of tissues and organs that support the head and neck. Human development is similar to that of other vertebrates, although there are some unique characteristics. The blood vessels of the pharyngeal arch are formed by the aortic arch arising from the aortic sac.
Structure of pharyngeal arch
The pharyngeal arches develop from the three best germ layers, which include ectoderm, mesoderm and endoderm. Neural crest cells also enter these arches, forming features of the skull and facial bones. However, the development of pharyngeal arches does not only depend on the presence of neural crest cells, but also has other developmental mechanisms that are independent of neural crest.
Biologists pointed out that Hox genes and other developmental genes such as DLX play a key role in the pattern formation of the pharyngeal arches.
The arches are numbered 1 to 6, with the first arch being closest to the head of the embryo, and the fifth arch being a transient structure that appears only during development. All pharyngeal arches gradually grow and connect at the midline of the abdomen, eventually forming a complex cavity system.
The development of the first bow
The first pharyngeal arch, also known as the mandibular arch, begins to develop in the fourth week. This arch is divided into the maxillary process and the mandibular process, which ultimately form the important structures of the face, such as the jaw and palate. This arch also provides the basis for the development of the muscles of mastication.
Meckel's cartilage in the mandibular arch eventually becomes some of the structures of the middle ear during development and serves as the template for the lower jaw.
The products of this arch include not only the structure of the skull, but also facial muscles, such as masticatory muscles, which all come from the mesoderm of the pharyngeal arch.
The role of the second bow
The second pharyngeal arch, or hyoid arch, appears primarily during the fourth week of development and helps form the sides and front of the neck. Reichert's cartilage in this arch will influence various structures in adulthood, such as the ossicles of the middle ear and the upper part of the hyoid bone.
In adults, these structures reflect the development of the second pharyngeal arch, which includes facial muscles such as the muscles of expression and some of the muscles of mastication.
This loose cartilage eventually becomes a mature structure, but as development progresses, parts of it disappear to form the latest anatomy.
Blood and nerve supply of the pharyngeal arches
Each pharyngeal arch has its own arterial and nerve supply. For example, the first arch is innervated by the trigeminal nerve, which provides nerve conduction to associated muscles and structures. The second arch is mainly controlled by the facial nerves, which not only affect the muscles of the face but also contribute to hearing function.
Similarities between humans and other vertebrates
Despite specific evolutionary differences between humans and other vertebrates, the function and anatomy of the pharyngeal arches are very similar across species. This allows biologists to study developmental processes between different species to understand how they evolved.
The presence of pharyngeal arches in some vertebrates demonstrates diverse genetic backgrounds and complexity of biological evolution.
In-depth exploration of the evolution of pharyngeal arches highlights an important question in the life process: What impact will these subtle evolutionary processes have on our appearance and function in future biological evolution?
