Development of the facial region, nasal and oral cavity

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Overview

The facial region and nasal–oral cavities arise primarily from the first pharyngeal arch and the frontonasal prominence. Their formation involves a complex sequence of growth, fusion, and remodeling of embryonic facial prominences between the 4th and 10th weeks of development. Precise coordination is crucial—small disturbances can lead to congenital malformations such as cleft lip, cleft palate, or nasal deformities.

Early craniofacial patterning and development.

Early Facial Development (Weeks 4–5)

1. Facial Prominences

By the end of the 4th week, five swellings appear around the primitive mouth (stomodeum):

1. Frontonasal prominence – unpaired, above the stomodeum
2. Two maxillary prominences – paired, from the first pharyngeal arch
3. Two mandibular prominences – paired, from the first pharyngeal arch

These structures surround the stomodeum, which is initially separated from the foregut by the oropharyngeal membrane (ruptures at ~day 26).

Development of the Facial Features

1. Frontonasal Prominence and Nasal Placodes

• On the lateral aspects of the frontonasal prominence, ectodermal thickenings appear—nasal placodes—which represent the early nasal epithelium.
• Each placode invaginates to form a nasal pit, surrounded by medial and lateral nasal prominences.
• The pits deepen to form nasal sacs, precursors of the nasal cavities.

2. Formation of the Upper Face

• The medial nasal prominences fuse with each other in the midline to form the intermaxillary segment, which gives rise to:
  • The philtrum of the upper lip
  • The premaxilla (bearing the four incisor teeth)
  • The primary palate
• The maxillary prominences grow medially and fuse with both the medial and lateral nasal prominences, forming:
  • The upper cheek regions
  • The lateral portions of the upper lip

Failure of fusion between maxillary and medial nasal prominences leads to a cleft lip (unilateral or bilateral).

3. Formation of the Lower Face

• The mandibular prominences merge in the midline to form:
  • The lower lip
  • The lower jaw (mandible)
  • The chin

This is the first part of the face to form and close.

Development of the Nasal Cavity

1. Formation of Nasal Sacs

As the nasal pits deepen, they form nasal sacs that are separated from the oral cavity by the oronasal membrane.

Around week 6, this membrane ruptures, creating the primitive choanae, connecting the nasal and oral cavities.

2. Separation by the Palate

• With the growth of the secondary palate (see below), the definitive choanae move posteriorly to open into the nasopharynx.
• The nasal septum develops from the frontonasal prominence and grows downward to fuse with the palatal shelves, dividing the nasal cavity into right and left halves.
• Ectodermal invagination forms the olfactory epithelium, from which olfactory receptor neurons differentiate.

Development of the Oral Cavity and Palate

1. Primary Palate

Derived from the intermaxillary segment (fusion of the medial nasal prominences), it forms:

• The anterior portion of the hard palate
• The region of the maxillary incisors

2. Secondary Palate

• Arises from palatine shelves (outgrowths of maxillary prominences) around week 6.
• Initially positioned vertically beside the tongue; later, the tongue drops and the shelves elevate to a horizontal position and fuse in the midline by week 9.
• Fusion occurs with:
  • The primary palate anteriorly
  • The nasal septum superiorly

3. Definitive Palate

The fusion of primary and secondary palates completes by week 10, forming the roof of the oral cavity and the floor of the nasal cavity.

Clinical relevance:

• Failure of fusion of the palatal shelves → cleft palate.
• Failure of fusion between primary and secondary palate → anterior cleft (involving the lip or premaxilla).
• Clefts may occur alone or in combination with cleft lip.

Formation of the Oral Cavity Proper

• The stomodeum becomes the oral cavity after rupture of the oropharyngeal membrane.
• The epithelium of the oral cavity originates from ectoderm, while its underlying tissues (muscle, connective tissue) come from mesoderm of the first arch and neural crest cells.
• Tongue development arises from the first four pharyngeal arches, with the anterior two-thirds from the first arch (lingual swellings and tuberculum impar) and the posterior third from arches three and four.

Clinical Correlations

• Cleft Lip: Failure of fusion between maxillary and medial nasal prominences.
• Cleft Palate: Failure of fusion between palatine shelves or between shelves and nasal septum.
• Oblique Facial Cleft: Failure of fusion between maxillary and lateral nasal prominences.
• Median Cleft Lip: Failure of fusion between the two medial nasal prominences.

Sources

• Moore, K.L., Persaud, T.V.N., Torchia, M.G. The Developing Human: Clinically Oriented Embryology.
• Sadler, T.W. Langman’s Medical Embryology.
• Larsen, W.J. Human Embryology.
• Netter, F.H. Atlas of Human Embryology.
• Carlson, B.M. Human Embryology and Developmental Biology.