EMBRYOLOGY OF SALIVARY GLANDS

PREPARED BY:Dr.Bayad Jaza Mahmood

Contents Introduction   Development of the major salivary glands: 1.parotid glands. 2.submandibular glands. 3.sublingual glands.   Development of the minor salivary glands and Von Ebner.

Summary.

References

Embryology:(from Greek embryon, "unborn, and -logia) is a science which is about the development of an embryo from the fertilization of the ovum to the fetus stage.

1. The innermost layer, or endoderm, gives rise to the digestive organs, lungs and bladder.

2. The middle layer, or mesoderm, gives rise to the muscles, skeleton and blood system.

3. The outer layer of cells, or ectoderm, gives rise to the nervous system and skin.

-logia

Three distinct layers of cells (the germ layers) from which all the bodily organs and tissues then develop:

o The development of salivary glands during the gestational period is important because these are actively involved in during postnatal life in the digestive processes ,body defense and speech.

o Thus, over the sixth and seventh weeks of embryonic period, the primitive salivary glands appear from the primitive oral cavity.

o According to the size present these glands in the adult there are two types of salivary glands: major salivary glands (parotid, submandibular gland, sublingual gland) and minor salivary glands and von Ebner.

INTRODUCTION

DEVELOPMENT OF THE PAROTID GLAND

The parotid glands are the first to appear (at the beginning of the sixth week). They develop from buds that arise from the oral ectodermal lining around the corners of stomodeum.

The buds grow and branch to form solid cords with rounded ends.

Subsequently, the laces are channeled and become conduits to the

10th week.

The rounded ends of the cords differentiate into acini.

Secretions begin early in the 18th week.

The capsule and connective tissue develops from the

surrounding mesenchyme.

Duct Canalization: Canalization results from mitotic activity of the

outer layers of the cord outpacing that of the inner cell layers.

Canalization is complete by 6th month post conception.

Acinar cells of Salivary Glands are classified: Serous cells: produce a thin watery secretion Mucous cells: produce a more viscous secretion

DEVELOPMENT OF SUBMANDIBULAR GLANDS

Submaxillary glands appear at the end of the 6th week.

They are formed from endodermal buds on the floor of stomodeum.

Grow posteriorly in the solid cell processes, lateral to the tongue and later branch out and differentiate.

Acini begin to form at the 12th week and the secretory activity

begins at the 16th week.

The growth of submandibular glands at birth continued after the formation of mucous acini. On one side of the tongue forms a linear groove which soon closes above and results in the submandibular duct.

DEVELOPMENT OF SUBLINGUAL GLAND

Sublingual glands appear during the eighth week, two weeks after the rest of the salivary glands.

Develop from multiple endodermal epithelial bud in the groove paralingual.

These buds branch and channelize to be 10 to 12 ducts that open independently on the floor of the mouth.

DEVELOPMENT OF MINOR SALIVARY GLANDS (VON EBNER)

Minor salivary glands are distributed in the submucosa of the oral cavity and are called according to the region that include: lip, palate, tongue, and palatoglossal junction.

Their secretions represent just under 10% of the total salivary volume, but they have great importance both locally and generally in relation to the defensive functions and digestive saliva.

  Most of the minor salivary glands have a mixed

structure, with a predominance of mucous components. The exception is the Von Ebner glands and lingual later, the only pure serous,

Von Ebner glands Are of endodermal origin.

They are found in circumvallate papillae of the tongue.

They secrete a serous fluid that begin lipid hydrolysis, and they facilitate the perception of taste.

They Begin to develop between the 8th and 10th week of intrauterine life. Between the 16th and 20th week acini and ducts are observed.

At 20th weeks of embryonic development both acini and ductal system are structurally distinct.

whose structure closely resembles the parotid gland. However, the secretory units of the Von Ebner glands do not consist of true acini but tubulosaccular dilated structures.

SUMMERY

The process of embryogenesis is common to all the salivary glands and each originates from a specific location stomodeum mucosa.

First there is a thickening of the epithelium at the site where pour gland secretions, hence an epithelial bud arises as a solid cellular cord which invaginates into the underlying connective tissue formation and dichotomous branching at its distal end.

Key points to review: The parotid primordium are the first to develop, followed by the

submandibular gland, and finally the sublingual gland. Parenchymal tissue (secretory) of the glands arises from the

proliferation of oral epithelium.

The stroma (capsule and septae) of the glands originates from mesenchyme that may be mesodermal or neural crest in origin.

Although the parotid primordium are the first to develop, they become encapsulated AFTER the SMG and SLG.

This delayed encapsulation is critical after the encapsulation of the SMG and SLG but BEFORE encapsulation of the parotid, the lymphatic system develops.

Therefore, there are intraglandular lymph nodes and lymphatic channels entrapped within the parotid gland (PG).

PG is also unique because its epithelial buds grow, branch and extend around the divisions of the facial nerve.

Elongation of the end bulb follows and lumina appears in their centers, transforming the end bulbs into terminal tubules.

These tubules join the canalizing ducts to the peripheral acini.

REFERENCES

Clinical embryology / Seventh Edition / Editorial ELSEVIIER / Madrid Spain – 2004.

Basic Embryology Patten / Editorial Mc Graw – Hill / Mexico – 1990.

  Atlas of human anatomy / Frank H. Netter / Second

Edition / Editorial Masson SA / Madrid Spain – 2000.   Sobotta Atlas of Human Anatomy / Ferrer, Helmut

Staubesand, Jochen.   Internet for pictures.

Thanks Dubai Towers