HE L5.1

Development of the Face and Neck

Introduction

• Reference: Development of the Face and Neck Handout (Copyright © 2011, 2006 by Saunders, Elsevier Inc.)

Overview of Facial Development

• Begins in the fourth week of prenatal development during the embryonic period.

• Rapidly growing brain bulges over the oropharyngeal membrane and heart.

Key Stages of Facial Development

• Facial Formation: Includes the primitive mouth, mandibular arch, maxillary process, frontonasal process, and nose.

• Dependent on five facial processes surrounding the primitive mouth:

  • Single frontonasal process

  • Paired maxillary and mandibular processes

Growth and Fusion of Facial Tissues

• Most facial tissues form by fusion of swellings on the same surface of the embryo.

• Initial formation includes a cleft or furrow between adjacent swellings caused by proliferation, differentiation, and morphogenesis.

• With fusion, furrows are usually eliminated as mesenchyme migrates, making the facial surface smooth.

Stomodeum and Oral Cavity Formation

• Stomodeum appears as a shallow depression in the ectoderm at the cephalic end before the fourth week.

• Limited in depth by the oropharyngeal membrane, separating it from the primitive pharynx (cranial part of foregut).

• Disintegration of the oropharyngeal membrane enlarges the stomodeum, allowing access between the stomodeum and pharynx.

• Mandibular processes fuse to form the mandibular arch below the stomodeum.

Mandibular Arch and Lower Face Formation

• Two bulges, the mandibular processes, appear below the primitive mouth within the fourth week.

• These processes fuse at midline to form the mandibular arch, contributing to the future lower dental arch.

• Indicates fusion at the mandibular symphysis on the mature mandible's surface.

• The mandibular arch gives rise to:

  • Lower face including the lower lip

  • Mandibular teeth and associated tissues

Frontonasal Process and Upper Face Formation

• The frontonasal process is a bulge of tissue in the upper facial area at the embryo's cephalic end.

• Contains placodes, specialized ectoderm areas for developing sense organs.

Nose and Paranasal Sinus Formation

• Nasal placodes undergo growth in the fourth week, initiating development of the nasal region and nose.

• Placodes submerge forming nasal pits (olfactory pits) between crescent-shaped swellings:

  • Medial nasal processes (middle)

  • Lateral nasal processes (outer part)

Intermaxillary Segment Development

• Formed from fused medial nasal processes inside the stomodeum.

Maxillary Process and Midface Formation

• Maxillary processes form from increased growth of the mandibular arch on each side of the stomodeum.

• Grow superiorly and anteriorly around the stomodeum.

Upper and Lower Lip Formation

• Upper lip formed when each maxillary process fuses with the medial nasal processes by mesenchymal growth.

Development of Pharynx

• Foregut develops into the primitive pharynx, forming the oropharynx.

Development of Branchial Arches

• Branchial arches (pharyngeal arches) appear in the fourth week, with the mandibular arch as the first.

• Each arch contains its own cartilage, nerves, and muscular components.

• First two pairs are more developed and named, while the third has unnamed cartilage.

• Third arch contributes to parts of the hyoid bone formation.

Branchial Groove and Membrane Formation

• Branchial grooves appear between branchial arches; only the first groove yields a definitive head and neck structure.

Pharyngeal Pouch Formation

• Four pairs of pharyngeal pouches develop as endodermal evaginations, ballooning between branchial arches in craniocaudal sequence.