The frontonasal process, or frontonasal prominence is one of the five swellings that develop to form the face. The frontonasal process is unpaired, and the others are the paired

maxillary prominence Continuous with the dorsal end of the first pharyngeal arch, and growing forward from its cephalic border, is a triangular process, the maxillary prominence (or maxillary process), the ventral extremity of which is separated from the mandibular a ...

s, and the paired

mandibular prominence The mandibular prominence is an embryological structure which gives rise to the lower portion of the face. The mandible and lower lip derive from it. The mesenchymal cells within the mandibular prominence condense to form Meckel's cartilage In hu ...

s. During the fourth week of

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 ...

, an area of thickened

ectoderm The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from t ...

develops, on each side of the frontonasal process called the

nasal placode The nasal placode (or olfactory placode) gives rise to the olfactory epithelium of the nose. Two nasal placodes arise as thickened ectoderm from the frontonasal process. They give rise to the nose, the philtrum of the upper lip, and the primary pa ...

s or olfactory placodes, and appear immediately under the

forebrain In the anatomy of the brain of vertebrates, the forebrain or prosencephalon is the Anatomical terms of location#Directional terms, rostral (forward-most) portion of the brain. The forebrain (prosencephalon), the midbrain (mesencephalon), and hin ...

. By invagination these areas are converted into two nasal pits, which indent the frontonasal prominence and divide it into medial and lateral nasal processes.

Nasal processes

The medial nasal process (nasomedial) on the inner side of each nasal pit merge into the

intermaxillary segment The intermaxillary segment in an Human embryo, embryo is a mass of tissue formed by the merging of tissues in the vicinity of the nose. It is essential for human survival. It is primordial, since in the further development of the embryo this part ...

and form the

upper lip The lips are the visible body part at the mouth of many animals, including humans. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech. Human lips are a tactile sensory organ, and can be ...

, crest, and tip of the

nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for respiration alongside the mouth. Behind the nose are the olfactory mucosa and the sinuses. Behind the nasal cavity, air next passes th ...

. The medial nasal processes merge with the maxillary prominences. The lateral nasal process from each side merge to form the alae of the

Clinical significance

Failure to fuse can cause a

cleft lip A cleft lip contains an opening in the upper lip that may extend into the nose. The opening may be on one side, both sides, or in the middle. A cleft palate occurs when the palate (the roof of the mouth) contains an opening into the nose. The te ...

Genetics

There is some evidence that development involves

Sonic hedgehog Sonic hedgehog protein (SHH) is encoded for by the ''SHH'' gene. The protein is named after the character ''Sonic the Hedgehog''. This signaling molecule is key in regulating embryonic morphogenesis in all animals. SHH controls organogenesis and ...

and

Fibroblast growth factor 8 Fibroblast growth factor 8 (FGF-8) is a protein that in humans is encoded by the ''FGF8'' gene. Function The protein encoded by this gene is a member of the fibroblast growth factor (FGF) family. FGF family members possess broad mitogenic and ...

References

External links

*
Flash animation at indiana.edu
* Embryology {{developmental-biology-stub