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Organ system development
Development of the cardiovascular system
Development of the ear
Development of the eye
Development of the face and palate
Pharyngeal arches, pouches, and clefts
Development of the digestive system and body cavities
Development of the gastrointestinal system
Development of the teeth
Development of the tongue
Development of the integumentary system
Development of the axial skeleton
Development of the limbs
Development of the muscular system
Development of the nervous system
Development of the renal system
Development of the reproductive system
Development of the respiratory system
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Branchial Pouches: 1st Pouch
Branchial Pouches: 2nd Pouch
Branchial Pouches: 3rd Pouch
Branchial Pouches: 4th Pouch
Pharyngeal Arch Derivatives: 1st Arch
Pharyngeal Arch Derivatives: 2nd Arch
Pharyngeal Arch Derivatives: 3rd Arch
Pharyngeal Arch Derivatives: 4-6 Arches
branchial arch derivation p. 640
branchial arch derivative p. 640
branchial arches derivation p. 639
Early in development, the embryo is a flat, disc-shaped organism made up of three layers of pluripotent cells called germ layers: an inner layer, called endoderm, a central layer, called mesoderm, and an outer layer, called ectoderm.
These three specialized cell layers give rise to all the organs and tissues in the body.
By week 4 of development, the embryo takes on a more recognizably human form—but to be honest, it still looks more like a shrimp than a baby.
At the cranial (head) end of this little shrimp-like creature, a set of structures called the pharyngeal apparatus begins to develop, consisting of pharyngeal arches, clefts, and pouches.
The pharyngeal apparatus starts forming around weeks 4 and 5, when six little bars of mesoderm, the pharyngeal arches, sprout from the primitive pharynx.
The pharyngeal arches develop in a craniocaudal fashion—meaning they form at the head and continue developing towards the tail end of the fetus.
These paired, symmetrical bumps are numbered from 1 to 6—it’s important to note that the fifth arch either never forms, or it quickly regresses, so it doesn’t develop into any structures.
Between the five pharyngeal arches, four pharyngeal clefts form and cover the external part of the corresponding arch with ectoderm cells, while four pharyngeal pouches line the internal part of their corresponding arches with endoderm.
The components of the pharyngeal apparatus develop into various head and neck structures, and sometimes multiple arches join together to give rise to a single structure.
Each pharyngeal arch, with its associated pouch and cleft, carries its own cranial nerve that innervates the structures that develop from that arch.
Pharyngeal arches, pouches, and clefts are structures that develop in the embryonic stage of human development and are involved in the formation of various head and neck structures, including the face and ears. The pharyngeal arches are derived from mesoderm and give rise to many of the bones and muscles in the head and neck. The pharyngeal clefts derive from the ectoderm, forming structures in the ear canals. The pharyngeal pouches arise from endoderm cells, and these form parts of the ears, as well as the early tonsils, and many portions of the parathyroid glands and thyroid.
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