Anatomy & Organs

Gill Arch – Structure, Function & Diseases

Germ arches

The gill arch is a six-part anatomical system in the early embryonic phase of humans. Various parts of the human body develop from the six relatively independent gill arches during later pregnancy . If the gill arch is affected by developmental disorders, the fetus may be deformed.

What is the gill arch?

The head gut of all vertebrate embryos proliferates into what is known as the gill arch. These are gill-like folds that are only relevant to the fetus and its development. Anatomical structures are formed from them by the time they are born . In humans, the gill arch develops during the early embryonic period.

Between the third and fifth week of embryonic development, the embryonic connective tissue already proliferates and forms a total of six arches. Only four of these are relevant for the later development of the fetus. The fifth gill arch is only rudimentary in all mammals. When viewed from the inside, the gill arches appear with gill folds or pharyngeal pouches. Externally, they correspond to gill sulci. The anatomical structure of the gill arch is also known as the bronchial arch or pharyngeal arch. It is also sometimes referred to as the pharyngeal arch or visceral arch.

Anatomy & Structure

The individual gill arches of humans are completely metameric, i.e. structurally identical. During embryonic development, a germ layer forms in each branchial arch, from which a cartilage , nerve , artery , and muscle later grow. These structures can be assigned to each gill arch individually.This means that they do not form a coherent system together, but exist as a self-contained system for the associated gill arch. The first and second branchial arches develop first. This development is followed by the formation of the third and fourth gill arches. The fifth bow is hardly put on. The sixth merges into the fourth later in the embryonic phase. The internal pharyngeal pouches are directly related to the gill arches and make up a total of five separate structures.

Function & Tasks

Organs develop from the gill arches of the embryo in the later development phase of the fetus. These organs are also known as branchiogenic organs. The first gill arch forms part of the face . This primarily includes the parts of the jaw, the palate and the auditory ossicles, the hammer and anvil. The first branchial arch nerve later becomes the fifth cranial nerve .

His muscular system becomes the masticatory muscles, with his own artery largely regressing. The stirrup forms from the second gill arch. The superior hyoid bone and temporal bone also arise from the second branchial arch. The artery of this arch later regresses. His nerve becomes the seventh cranial nerve and his musculature develops into facial muscles in particular. The lower hyoid bone later develops from the third gill arch . Its muscle becomes the style-throat muscle, with its artery becoming the internal carotid artery.

Its nerve later forms the ninth cranial nerve, the so-called tongue-pharyngeal nerve. In particular, the larynx , together with the larynx and pharyngeal muscles, develop from the fourth gill arch in conjunction with the sixth gill arch . Its artery becomes the aortic arch and subclavian artery. Along with portions of the sixth branchial arch, the fourth branchial nerve also develops into the tenth cranial nerve. The merely rudimentary fifth gill arch does not form any definite structures.

On the other hand, anatomical structures do develop from the five pharyngeal pouches or gill slits of the gill arch during the embryonic phase. The first pharyngeal pouch specifically becomes the auditory tube and the auditory canal . The second pharyngeal pouch becomes the tonsils of the palate. The third and fourth make up the parathyroid and thymus glands . The fifth pharyngeal pouch becomes C cells, which later populate the thyroid .

Diseases

The gill arch can be affected by embryonic developmental disorders. Such a developmental disorder could possibly be due to nicotine or alcohol consumption during pregnancy. The cleft lip and palate is one of the most well-known phenomena associated with a developmental disorder of the branchial arch.In the gill arch, individual parts of the face develop separately and later grow together. If these individual parts do not fuse or only partially fuse in the seventh week of pregnancy, a deformed premaxillary segment can form, for example. The maxillary ridges from certain parts of the gill arch later grow together with the nasal ridges . They form the left and right part of the upper lip and also form the individual sides of the upper jaw. If this development is disrupted or relevant tissue parts open up again in the course of development, a cleft jaw or cleft lip develops, which can be unilateral or bilateral.

Many other abnormalities of the jaw or teeth can be traced back to developmental disorders of the branchial arch. For example, Goldenhar syndrome is a congenital malformation syndrome that can result in asymmetrical corners of the mouth , underdeveloped cheeks and jawbones, small ears , narrow eyelids, and even missing eyes . The children are often also affected by a heart defect , kidney damage or hearing and tooth damage .

Medicine now assumes that the cause of the syndrome is a thrombus in the tissue of the first and second branchial arch and the first pharyngeal pouch. The thrombus is presumably preceded by an interrupted blood supply to these tissues. Little is known about the causes of such a circulatory disorder . The syndrome should not be hereditary.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.