Lecture 5 - Oro Facial Development

Page 1: Development of the Face and Neck

• Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Page 2: Overview of Facial Development

• Facial development begins during the fourth week of prenatal development.

• The rapidly growing brain bulges over the oropharyngeal membrane and heart.

Page 3: Embryo at Fourth Week

• Figure 4-1 (Visual depiction of the embryo's development).

Page 4: Overview of Facial Development

• The formation of the primitive mouth, mandibular arch, maxillary process, frontonasal process, and nose occurs during this stage.

• Five facial processes (prominences) surround the primitive mouth:

  • Frontonasal process (single)

  • Maxillary processes (paired)

  • Mandibular processes (paired)

Page 5: Adult Face and Its Embryonic Derivatives

• Figure 4-3 (Illustration showing adult face compared to embryonic structures).

Page 6: Overview of Facial Development

• Facial tissues primarily develop by fusing swellings on the embryo's surface.

• Initially, clefts or furrows between adjacent swellings appear due to proliferation and morphogenesis.

Page 7: Fusion

• Figure 4-4 (Visual representation of facial fusion).

Page 8: Overview of Facial Development

• During facial fusion, furrows are eliminated as mesenchyme migrates into the furrows, smoothing the facial surface.

• This migration happens as mesenchyme grows and merges beneath the ectoderm.

Page 9: Stomodeum and Oral Cavity Formation

• The primitive mouth is known as the stomodeum, appearing as a shallow depression before week four.

• The stomodeum is limited in depth by the oropharyngeal membrane.

Page 10: Stomodeum and Oral Cavity Formation

• The oropharyngeal membrane separates the stomodeum from the primitive pharynx (cranial part of the foregut).

Page 11: Stomodeum and Oral Cavity Formation

• Disintegration of the oropharyngeal membrane enlarges the stomodeum, enabling access between the primitive mouth and pharynx.

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

Page 12: Figure 4-5

• Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Page 13: Mandibular Arch and Lower Face Formation

• Two tissue bulges appear as the mandibular processes beneath the primitive mouth.

• These processes consist of mesenchyme, partly originating from neural crest cells, and are covered by ectoderm and endoderm.

Page 14: Mandibular Arch and Lower Face Formation

• The paired mandibular processes fuse at the midline to become the mandibular arch, the precursor to the lower dental arch and mandible.

• Following fusion, the mandibular arch extends below the stomodeum and lies between the developing brain and heart.

Page 15: Mandibular Arch and Lower Face Formation

• The mandibular symphysis indicates where the mandible is formed by the fusion of the left and right mandibular processes.

Page 16: Mandibular Arch and Lower Face Formation

• The mandibular arch forms the lower face and lower lip, contributing to the mandible and its associated teeth and tissues.

Page 17: Frontonasal Process and Upper Face Formation

• A bulge of tissue, the frontonasal process, develops at the upper facial area by the fourth week as the cranial boundary of the stomodeum.

• Placodes (thickened ectoderm) on the embryo’s outer surface mark the sites of developing special sense organs.

Page 18: Nose and Paranasal Sinus Formation

• Tissue around the nasal placodes on the frontonasal process begins growing, leading to nose development.

• Nasal placodes become submerged, forming nasal pits (olfactory pits).

Page 19: Figure 4-6

• Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Page 20: Nose and Paranasal Sinus Formation

• The area around the nasal placodes shows crescent-shaped swellings:

  • Medial nasal processes (located between nasal pits)

  • Lateral nasal processes (located on the outer side of the nasal pits).

Page 21: Development of Intermaxillary Segment

• The intermaxillary segment develops from the fused medial nasal processes within the stomodeum.

Page 22: Figure 4-7

• Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Page 23: Maxillary Process and Midface Formation

• A maxillary process, formed from the mandibular arch, grows around the stomodeum during the fourth week, moving superiorly and anteriorly.

Page 24: Upper and Lower Lip Formation

• The upper lip forms when each maxillary process fuses with each medial nasal process on both sides of the stomodeum, influenced by the growth of the mesenchyme.

• The maxillary processes shape the sides of the upper lip, while the medial nasal processes form the philtrum.

Page 25: Development of Pharynx

• The foregut develops into the primitive pharynx, which will subsequently form the oropharynx.

Page 26: Development of Pharynx

• Figure 4-10 (Illustration related to pharynx development).

Page 27: Development of Branchial Arches

• During the fourth week, bilateral tissue swellings appear under the stomodeum, forming the branchial arches, with the mandibular arch being the first.

Page 28: Branchial Arches and Derivative Structures

• Figure 4-11 (Illustration showing branchial arches and their derivatives).

Page 29: Development of Branchial Arches

• Each paired branchial arch has its cartilage, nerve, vascular, and muscular components.

• The first two pairs of arches are the most prominent, while the third has unnamed cartilage contributing to the hyoid bone structure.

Page 30: Branchial Groove and Membrane Formation

• Branchial grooves appear between the branchial arches; only the first groove contributes to a mature structure in the head and neck.

Page 31: Pharyngeal Pouch Formation

• Four pairs of pharyngeal pouches develop as endodermal evaginations lining the pharynx, forming balloon-like structures between branchial arches.