بسم الله الرحمن الرحيم

Oral Mucous Membrane

Objectives: At the end of this subject students should know thoroughly: 1- The definition & function of oral mucous membrane. 2- The classification of oral mucous membrane. 3- The histological structure of the mucous membrane. 4- The differences between the two different types of the oral epithelium. 5- Keratinocytes and non keratinocytes. 6- The macro &micro-anatomy of the gingiva. 7- The macro &micro-anatomy of the hard palate. 8- The different types of lining mucosa. 9- The specialized mucosa and the different types of the papillae. 10- Dento-gingival junction (Histology and Histogenesis)

Mucous membrane Hard palate Dorsal surface of the tongue Check mucosa Floor of mouth Gingiva Ventral surface of the tongue Vestibular fornix Alveolar mucosa Labial mucosa

Definition -It is that membrane which lines a body cavity that communicates to outside and coated with serous and or mucous secretion. - Its epithelial cells have a high rate of turnover. - It possesses a stratified epithelium which is keratinized in many places and prevents or limits diffusion across it in both directions.

Functions of oral mucosa 1- Protective It protects the underlying structures from mechanical, chemical and thermal effects of food taken. It acts as a biological barrier against bacteria and invasion of their toxins. 2- Sensory It has multi nerves that respond to temperature, touch and pain as well as to taste sensation. Certain receptors in the oral mucosa initiate reflexes such as swallowing, gagging, salivation and water satisfaction.

3- Thermal regulation In animals through the evaporation of water from the surface mucosa . Human oral mucosa plays a minor role in this respect. 4- Secretory Salivary secretion keeps it always moist and provides it with additional protective means.

Classification of oral mucous membrane 1-Keratenized mucosa ( Masticatory mucosa) (A) Gingiva (B) Hard palate 2- Non-keratenized mucosa (Lining mucosa) (A) Firmly attached (B) Loosely attached I- Soft palate I- Floor of mouth II-Vestibule II-lip III-check IV-ventral S tongue III-alveolar mucosa 3- Specialized mucosa Dorsal surface of the tongue

Histological structure: The human oral mucosa consists of: Epithelium. & Lamina propria, a connective tissue supporting layer. Both of these two layers are separated by a basement membrane and attached either directly to the underlying structures or through a submucous layer.

Keratenized epithelium Non-keratenized epithelium 1- The oral epithelium: It is stratified squamous epithelium keratinized in certain areas and non-keratinized in others. Keratenized epithelium Non-keratenized epithelium

A-The keratinized epithelium: Found in gingiva and mucosa of hard palate, which are subjected directly to the mechanical effect of food during mastication. The cells are arranged in four different layers: Basal (stratum basale) Spinous (stratum spinosum) Granular (stratum granulosum) Cornified (stratum cornium). Stratum cornium Stratum granulosum Stratum spinosum These cells are called Keratinocytes. Stratum basale

These cells have the following criteria: a- Always attached to each other by one or more type of cellular junctions. b- The cytoplasm of these cells is stained with ordinary stain as H & E. c- Their cytoplasm contains characteristic tonofilaments.

*The cells of the basal and spinous layer are named stratum germinativum or progenitor cells. *Daughter cells pass towards the surface and during the process of maturation, take on the appearance characteristic of the various layers.

a. Basal Cell layer (stratum Basal). -It consists of a single layer of high cuboidal cells rest on the basement membrane. -Protoplasmic process projecting from their basal end towards the C.T.

By the E. M. - The cytoplasm contains tonofibrils forming desmosomes and hemi -desmosomes which attach the cells to one another and to the Basal lamina. - The desmosomes consist of thickening of adjacent cell membrane a pair of attachment plaques and intervening extra cellular structure and tonofilaments. - The hemidesmosomes consist of a single attachment plaque. Thickening of one cell membrane extracellular structure that attach the epithelium to the Basal lamina and tonofilaments.

The desmosomes 1- Thickening of the adjacent cell membrane. 2- A pair of attachment plaque. 3- Tonofilaments. 4- Extracellular structure.

The hemi-desmosomes and basal lamina Both layers derived from the basal cell layer

b-The spinous cell layer (Stratum Spinosum). - Above the basal cell layer. - Formed of several layers of polyhedral cells joined by long intercellular Bridges which gives the cells a prickly appearance. They are small in size with wide intercellular spaces.

2. Well developed Golgi apparatus. By the E.M. The prickle cells are the most active in protein synthesis so they contain: 1- Nuclei show widely spread chromatin. 2. Well developed Golgi apparatus. 3. Rough endoplasmic Reticulum with its Ribosomes. 4. Numerous Mitochondria. There is a progressive decrease in synthetic activity through the layer directed to the surface. Low synthetic activity High synthetic activity

Odland Bodies or Keratinosome : - They are membrane coating granules. - Present in the superficial layer of the prickle cells. - It has an internal Lamellated structure. - It may originate from the Golgi system. They are present also in the lower granular cell layers. Odland body

Role of Odland bodies -These structures are responsible for the thickening of the cell membrane which occurs during Keratinization. -In the more superficial layers of the stratum spinosum the granules come to lie close to the cell membrane.

c-The granular cell layer Lies above the prickle cell layer and is made up of several rows. - Cells are Flat with degenerated and Pyknotic nuclei and many organelles are reduced - They synthesis protein also but with diminished rate.

-Cells contain basophilic granules called Keratohyaline granules. -These granules are 0.5-1.0 μm in length and form the matrix in which the tonofilaments are embedded. -The Odland Bodies are increased and discharged into the intercellular spaces. -This is associated with the development of a barrier in the epithelium that limits the movement of substances between the cells. -The tonofilaments are increased and associated with the Keratohyaline granules.

d-The cornified layer: - Made up of keratinized squamae which are larger and Flatter than the granular cells. -These cells are characterized by loss of all organelles -They are filled entirely with closely backed tonofilaments. -These cells finally will desquamate. -This layer provides the mechanical and chemical protective function to the mucosa.

2- Non keratinized epithelium Stratum superficial Stratum intermedium Odland body Stratum basal Non-keratenized epithelium

Non-keratinized oral epithelium: The epithelium is thicker than the keratinized one - It doesn’t produce cornified surface layer. - It has no stratum granulosum nor stratum cornium. - It has 3 cell layers.

1. Stratum Basal (Basal cell layer ). Similar to that of the Keratinized type. 2. Stratum Intermedium -Formed of large polyhedral cells with short intercellular Bridges and small intercellular spaces. -The cells do not have prickly appearance. -There are Odland bodies with different size and location than that in the Keratinized epithelium.

3. Superficial cell layer. (Stratum Superficial). It consists of nucleated flat cells which ultimately desquamate as the cornified layer. There is accumulation of glycogen and occasionally Kerato hyaline granules appear more regular and not associated with tonofilaments. Function of keratohyaline granules appear to be associated with thickening of the cell membrane. -These granules may contribute to the internal thickening of the cell membrane.

Keratinocytes and non-keratinocytes Keratinocytes are those cells of keratinized and non keratinized epithelium. Non Keratinocytes are: Melanocyte, Langerhans cell, Merkel ‘s cell and Inflammatory cells.

Criteria of Keratinocytes a- Always attached to each other by one or more type of cellular junctions. b- The cytoplasm of these cells is stained with ordinary stain as H & E. c- Their cytoplasm contains characteristic tonofilaments. Criteria of Non Keratinocytes a- They do not attach to each other or to the epithelial cells except Merkel’s cells. b- The cytoplasm of these cells does not stain by H & E. c- Their cytoplasm does not contain tonofilaments except Merkel’s cells.

1- Pigment cell (Melanocyte, blast) 3- Merkel’s cell 2- Langerhan’s cell 1- Pigment cell (Melanocyte, blast) They do not have long processes. Contain small membrane bounded granules Similar in shape. Contain granules (langerhan’s granules) Small body with long slender and branched process present in the Inter cellular spaces of epith. contain melanin granules (melanosomes) Shape Basally in epithelium High level cell and may be found at lower levels. Basal and parabasal layers Location Not stained so called ( Clear but not dentritic cell ) ( Clear dentritic cell ) Stain by H&E Gold chloride DOPA reaction ( for tyrosinase enzyme) Special stain

-Little tonofilaments. -Little desmosomes. Neural crest cells Bone marrow Origin -Little tonofilaments. -Little desmosomes. -Nerve cell seen to be associated with the cell with synapse-like cleft. No tonofilaments. No desmosomes. Cell junction Responding to touch. They may be described as 1-Neural element. 2- Degenerated melanocyte. 3- Intra epithelial Macrophage. 4- Regulatory cells (control epith. Cell division and differentiation) 5- Uptake and processing of antigen in contact allergic reaction Pigmentation. If melanosomes engulfed by epithelial cell called (Melanophore) or by C.T. cell (Melanophage). Function 4- Inflammatory cells They are transient cells

The lamina propria is divided into 2 layers, II- Lamina propria. The lamina propria is divided into 2 layers, 1- A superficial layer: loose connective tissue called the papillary layer which is formed of tall numerous papilla directly under the basement membrane and collagen fibers arranged in a loose network with fine argerophelic Fibers. Papillary layer

No line of demarcation is present between the two layers. 2-The deeper layer is made of dense and closely packed collagen fibers which are arranged in laminae, and this layer is called the Reticular layer. The papillary layer may be absent while the Reticular layer is always present. No line of demarcation is present between the two layers. Papillary layer Reticular layer

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