In the

embryonic development An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

s, pharyngeal pouches form on the endodermal side between the

pharyngeal arch The pharyngeal arches, also known as visceral arches'','' are structures seen in the embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the branchial arches, or gill arch ...

es. The

pharyngeal groove A pharyngeal groove (or branchial groove, or pharyngeal cleft) is made up of ectoderm unlike its counterpart the pharyngeal pouch on the endodermal side. The first pharyngeal groove produces the external auditory meatus (ear canal). The rest (2, ...

s (or clefts) form the lateral ectodermal surface of the neck region to separate the arches. The pouches line up with the clefts, and these thin segments become

gills A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

Specific pouches

First pouch

The

endoderm Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gast ...

lines the future

auditory tube Auditory means of or relating to the process of hearing: * Auditory system, the neurological structures and pathways of sound perception ** Auditory bulla, part of auditory system found in mammals other than primates ** Auditory nerve, also known ...

(Pharyngotympanic Eustachian tube),

middle ear The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear). The mammalian middle ear contains three ossicles, which transfer the vibrations of the eardrum into waves in the ...

mastoid antrum The mastoid antrum (tympanic antrum, antrum mastoideum, Valsalva's antrum) is an air space in the petrous portion of the temporal bone, communicating posteriorly with the mastoid cells and anteriorly with the epitympanic recess of the middle ear vi ...

, and inner layer of the tympanic membrane. Derivatives of this pouch are supplied by Mandibular nerve.

Second pouch

* Contributes the

palatine tonsils Palatine tonsils, commonly called the tonsils and occasionally called the faucial tonsils, are tonsils located on the left and right sides at the back of the throat, which can often be seen as flesh-colored, pinkish lumps. Tonsils only present as ...

, supplied by the

facial nerve The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of tas ...

Third pouch

* The third pouch possesses Dorsal and Ventral wings. Derivatives of the dorsal wings include the inferior

parathyroid gland Parathyroid glands are small endocrine glands in the neck of humans and other tetrapods. Humans usually have four parathyroid glands, located on the back of the thyroid gland in variable locations. The parathyroid gland produces and secretes pa ...

s, while the ventral wings fuse to form the cytoreticular cells of the

thymus The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or ''T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders. ...

. The main nerve supply to the derivatives of this pouch is Cranial Nerve IX,

glossopharyngeal nerve The glossopharyngeal nerve (), also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper Medulla oblongata, medulla, just anterior (closer to the nose) to t ...

Fourth pouch

Derivatives include: * superior

s and ultimobranchial body which forms the

parafollicular Parafollicular cells, also called C cells, are neuroendocrine cells in the thyroid. The primary function of these cells is to secrete calcitonin. They are located adjacent to the thyroid follicles and reside in the connective tissue. These cells a ...

C-Cells of the

thyroid gland The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobe (anatomy), lobes. The lower two thirds of the lobes are connected by a thin band of Connective tissue, tissue cal ...

. * Musculature and cartilage of larynx (along with the sixth pharyngeal arch). * Nerve supplying these derivatives is Superior laryngeal nerve.

Fifth pouch

* Rudimentary structure, becomes part of the fourth pouch contributing to thyroid C-cells.Endocrine Glands

Sixth pouch

* The fourth and sixth pouches contribute to the formation of the musculature and cartilage of the larynx. Nerve supply is by the recurrent laryngeal nerve.

References

External links

* (Item #1 at Fig. 14) * * *
Outline at howard.edu (scroll down to "III. THE PHARYNGEAL POUCHES")
{{Authority control Animal developmental biology Pharyngeal arches Human head and neck