Palate Development

Introduction

Fetal head (week 12)

The palate has two key stages of development during embryonic and an early fetal involving the fusion of structures (epithelia to mesenchymal).

Historic Head Embryology
1910 Skull \| 1910 Skull Images \| 1912 Nasolacrimal Duct \| 1921 Human Brain Vascular \| 1923 Head Subcutaneous Plexus \| 1919 21mm Embryo Skull \| 1920 Human Embryo Head Size \| 1921 43 mm Fetal Skull \| Historic Disclaimer

Some Recent Findings

A dosage-dependent role for Spry2 in growth and patterning during palate development^[1] "The formation of the palate involves the coordinated outgrowth, elevation and midline fusion of bilateral shelves leading to the separation of the oral and nasal cavities. Reciprocal signaling between adjacent fields of epithelial and mesenchymal cells directs palatal shelf growth and morphogenesis. Loss of function mutations in genes encoding FGF ligands and receptors have demonstrated a critical role for FGF signaling in mediating these epithelial-mesenchymal interactions. The Sprouty family of genes encode modulators of FGF signaling. We have established that mice carrying a deletion that removes the FGF signaling antagonist Spry2 have cleft palate."

Textbooks

The Developing Human: Clinically Oriented Embryology (8th Edition) by Keith L. Moore and T.V.N Persaud - Moore & Persaud Chapter Chapter 10 The Pharyngeal Apparatus pp201 - 240.
Larsen’s Human Embryology by GC. Schoenwolf, SB. Bleyl, PR. Brauer and PH. Francis-West - Chapter 12 Development of the Head, the Neck, the Eyes, and the Ears pp349 - 418.

Development Overview

Pharyngeal Arch Components

Major features to identify for each: arch, pouch, groove and membrane. Contribute to the formation of head and neck and in the human appear at the 4th week. The first arch contributes the majority of upper and lower jaw structures.

Early Face and Pharynx

Pharynx - begins at the buccopharyngeal membrane (oral membrane), apposition of ectoderm with endoderm (no mesoderm between)

Pharyngeal Arch Development

branchial arch (Gk. branchia= gill)
arch consists of all 3 trilaminar embryo layers
ectoderm- outside
mesoderm- core of mesenchyme
endoderm- inside

Neural Crest

Mesenchyme invaded by neural crest generating connective tissue components
cartilage, bone, ligaments
arises from midbrain and hindbrain region

Face Development

Begins week 4 centered around stomodeum, external depression at oral membrane

5 initial primordia from neural crest mesenchyme

single frontonasal prominence (FNP) - forms forehead, nose dorsum and apex
nasal placodes develop later bilateral, pushed medially
paired maxillary prominences - form upper cheek and upper lip
paired mandibular prominences - lower cheek, chin and lower lip

Frontonasal Process

The frontonasal process (FNP) forms the majority of the superior part of the early face primordia. It later fuses with the maxillary component of the first pharyngeal arch to form the upper jaw. Failure of this fusion event during the embryonic period leads to cleft lip. Under the surface ectoderm the process mesenchyme consists of two cell populations; neural crest cells, forming the connective tissues; and the mesoderm forming the endothelium of the vascular network.

A chicken developmental model study has identified a specific surface region, the Frontonasal Ectodermal Zone (FEZ), initially induced by bone morphogenetic proteins that appears to regulate the future growth and patterning of the frontonasal process. The specific frontonasal ectodermal zone was located in the frontonasal process ectoderm flanking a boundary between Sonic hedgehog (Shh) and Fibroblast growth factor 8 (Fgf8) expression domains.^[2]

Head Growth

continues postnatally - fontanelle allow head distortion on birth and early growth
bone plates remain unfused to allow growth, puberty growth of face

Embryonic Palate

Primary palate, fusion in the human embryo between stage 17 and 18, from an epithelial seam to the mesenchymal bridge.

Fetal Palate

Secondary palate, fusion in the human embryo in week 9. This requires the early palatal shelves growth, elevation and fusion during the early embryonic period. The fusion event is to both each other and the primary palate. palatal shelf elevation | secondary palate