Helwan University Lecture Notes on Oral Cavity (GIT module 104) PDF

Lecture (1) by: Dr. Shaimaa Zaher Lecturer of Histology Email: [email protected] Faculty of Medicine Helwan University objectives Identify p...

Lecture (1) by: Dr. Shaimaa Zaher Lecturer of Histology Email: [email protected] Faculty of Medicine Helwan University objectives Identify parts of the digestive system Describe the histology of different structures related to the oral cavity: Lips Cheeks Tongue Palate Pharynx  Digestive system Digestive tract Associated glands Lips Cheeks Oral cavity Tongue Palate Salivary glands Pharynx Liver Pancreas Gastrointestinal Esophagus tract Stomach (alimentary Small intestine Large intestine canal)  The function of the digestive system is to break down food for absorption into the body. This process occurs in five main phases: ingestion, mastication, digestion, absorption and elimination of waste products. The microscopic structure of each part of the digestive tract is adapted to reflect functional changes. The digestive tract is lined internally by mucous membrane (mucosa) Epithelium Lamina propria (loose connective tissue)  Oral cavity It is lined with oral mucosa (mucous membrane). Its epithelium is stratified squamous that may be keratinized, partially keratinized or nonkeratinized depending on the location. Oral mucosa Masticatory mucosa Lining mucosa ▪ It has keratinized stratified squamous ▪ It has non-keratinized stratified squamous epithelium. epithelium. ▪ It is found on areas subjected to ▪ It is found on inner surface of the lips, mechanical trauma during cheeks, floor of the mouth, inferior mastication of food e.g. the gingiva surface of the tongue, soft palate & (gums) and the hard palate. pharynx.  Lips The lips consist of a core of striated muscle (orbicularis oris) Thin skin Each lip has three covering surfaces: Vermilion Outer surface zone (thin skin) Striated muscle Vermilion zone (red margin) Inner surface mucous (mucous membrane) membrane The outer surface of the lip is thin skin consisting of epidermis (stratified squamous keratinized epithelium) & dermis with hair follicles, sebaceous glands & sweat glands. Epidermis Dermis Sebaceous glands Hair follicles Sweat glands Orbicularis oris muscle (T.S.) 6 The inner surface of the lip is lined by mucous membrane (lining oral mucosa) with minor salivary glands (labial glands). Epithelium Stratified squamous nonkeratinized Minor Lamina propria = C.T. containing labial glands (mucous secreting minor salivary glands) 7  The red vermilion zone (lip margin) is a transitional zone between skin and oral mucosa. It appears pinkish-red because of the relatively translucent epithelium and many blood capillaries in the underlying C.T. Epithelium (stratified squamous lightly keratinized ) Underlying C.T. - Very rich in blood capillaries and sensory innervation. - NO hair follicles. - No sweat nor sebaceous glands (so lip margin is kept moist with Blood vessels saliva) 8  Cheeks The cheek resembles the lip in histologic features. It consists of a core of striated muscle (Buccinator muscle) that is covered by skin from outside & lined by mucous membrane from inside. The epithelium of its lining mucosa is stratified squamous nonkeratinized. The lamina propria contains minor salivary (buccal) glands that extends in C.T. between muscle fibers. 9  Tongue ❖The tongue is a muscular organ. ❖It consists of a mass of striated muscle covered by oral mucosa. ❖It has 2 surfaces: dorsal (upper) & ventral (lower). ❖The dorsal surface is divided into an anterior two-thirds and a posterior one- third by a V-shaped depression, the sulcus terminalis. The apex of the V points posteriorly. 10 Histological structure of the tongue Mass of Dorsal surface Ventral surface striated muscle 1. The striated muscle fibers of the tongue ❖They are oriented in Bundles of 3 different directions (vertical, striated horizontal & longitudinal) muscle allowing a high level of fibers mobility essential of mastication, swallowing & phonation. 2. Dorsal surface of the tongue ❖ It is irregular as it contains lingual papillae on its anterior two-thirds and lingual tonsil on its posterior one-third. ❖ It is covered by partially keratinized stratified squamous epithelium. 3. Ventral surface of the tongue Lingual glands ❖ It is smooth. ❖ It is covered by typical lining mucosa (nonkeratinized stratified squamous epithelium). ❖ Lingual glands (mucous secreting minor salivary glands) are found in the deep part of the lamina propria & extend in-between the ventral portion of lingual muscles.  Lingual Filiform papillae Tongue Epithelium Fungiform Dorsal surface Lamina propria papilla striated muscle Lamina fibers propria Stratified squamous non- Ventral surface keratinized epithelium 14  lingual papillae Definition: epithelium Mucosal projections on the anterior two-thirds of the dorsal surface of the tongue. C.T. Structure: Each papilla has a core of connective tissue covered by stratified squamous epithelium (with variable degree of keratinization).  Types of lingual papillae: 1- Filiform papillae 2- Fungiform papillae 3- Circumvallate papillae 4- Foliate papillae 16  1- Filiform papillae Filiform papillae Number: the most numerous. Site: anterior 2/3 of the dorsum of the tongue. Shape: conical, with their tips directed posteriorly. Epithelium: stratified squamous striated muscle fibers heavily keratinized, which gives a whitish appearance. Taste buds: absent. Filiform papillae provide a rough surface that facilitates movement of food during chewing. 17  Fungiform papilla 2- Fungiform papillae Filiform papillae Number: less numerous. Site: interspersed among the filiform papillae. Shape: mushroom-shaped. Epithelium: stratified squamous lightly keratinized with highly vascularized connective tissue core (so appear as red spots by naked eye) Taste buds: few, present on the apical surface of papillae. 18  3- Circumvallate (vallate) papillae Number: 8- 12 (least common type). Site: just in front of the sulcus terminalis Shape: The largest papillae (1-3 mm). Dome-shaped. Each papilla is surrounded by a deep groove (cleft). Epithelium: stratified squamous Taste buds non-keratinized. Taste buds: numerous ((about 250 taste buds are present on the lateral surface (sides) of each vallate papilla)) Von Ebner glands Ducts of serous salivary glands (von Ebner St.ms glands) open into the base of the clefts. 19  von Ebner glands Definition: serous lingual minor salivary Circumvallate papilla glands. Site: in the connective tissue underlying circumvallate papillae. Ducts: open into the base of the clefts of vallate papillae. Taste buds Function: 1.Secretion of a watery fluid which dissolves food particles to facilitate taste reception. cleft 2. Continuous flow of this fluid over the taste buds washing away food particles so Ducts they can receive new taste stimuli. Von Ebner 3. This fluid contains a lipase enzyme that prevents formation of a hydrophobic glands layer on taste buds that would hinder gustation. 20  Circumvallate A deep groove (vallate) papilla (cleft) surrounds (SEM) the vallate papilla 21  4- Foliate papillae Number: rudimentary in humans especially in elderly individuals but are developed in young children. They are well developed in rabbits. Site: form parallel ridges on posterolateral margins of the anterior two-thirds tongue. Shape: Leaf-like. Each papilla is surrounded by a deep cleft. Epithelium: stratified squamous non-keratinized. Taste buds: numerous, present on the Foliate sides (lateral walls) of these papillae. papillae 22 stratified squamous non-keratinized Surrounded by epithelium deep clefts Serous glands open via ducts into the cleft 23  Foliate papillae stratified Taste buds squamous non- present on keratinized the lateral epithelium surfaces 24  Taste buds Taste buds Definition: they are neuroepithelial structures specialized for taste sensation. Sites: within the stratified epithelium of circumvallate, fungiform and foliate papillae (but NOT the keratinized filiform papillae). They are more abundant on circumvallate papillae. Shape: appear as oval pale staining bodies that extend through the thickness of the epithelium. A small opening at the apex of the taste bud is called the taste pore. Structure: consists of three types of cells Taste 1. Gustatory (taste, sensory) cells. pore 2. Supporting cells. 3. Basal cells.  1. Gustatory (taste, sensory) cells. They are the most numerous cells in the taste bud. They are elongated cells extending from the basal lamina of the epithelium to the taste pore. Their apical ends have microvilli projecting through taste pores. Their bases form synapses with afferent sensory axons that carry impulses of taste sensation. Food molecules dissolved in saliva contact the microvilli and interact with taste receptors found on microvilli.  2. Supporting cells less numerous. They are elongated cells that extend from the basal lamina to the taste pore. Support the gustatory cells. 3. Basal cells They are small cells located in the basal portion of the taste bud, near the basal lamina. They are the stem cells for the other two cell types. Taste buds Nerve fibers Taste buds (NF) Taste Pore (TP) 28  Palate ✓The palate forms the roof of the mouth and separates oral and nasal cavities. ✓The anterior part is the hard palate (its core is bone). ✓ The posterior part is the soft palate (its core is skeletal muscle). ✓The nasal aspect of the palate is lined by pseudostratified columnar ciliated epithelium with goblet cells (respiratory epithelium). ✓Oral aspect of the hard palate is lined by masticatory mucosa (stratified squamous keratinized epithelium). ✓Oral aspect of the soft palate is lined by stratified squamous non-keratinized epithelium. ✓Lamina propria of the palate contains palatine glands (minor salivary glands) Hard palate Bone Lamina propria Stratified squamous keratinized epithelium  Pharynx It is a transitional tube that conducts food to the esophagus and air to the larynx. It is divided into 3 parts Nasopharynx: lies posterior to nasal cavities & lined with respiratory epithelium. Oropharynx: it the posterior part of oral cavity & lined with stratified squamous non-keratinized epithelium Laryngopharynx: lined with stratified squamous non-keratinized epithelium Pseudostratified columnar ciliated epithelium stratified squamous non-keratinized epithelium with goblet cells (respiratory epithelium). Nasopharynx Oropharynx The dorsal surface of a tongue specimen is examined at high magnification (shown in the image). Which of the following describes the most likely function of the structure indicated by the arrow? (A) Pain receptor (B) Response to bitter taste (C) Surface for food movement (D) Temperature receptor 33 A lip biopsy is sectioned and prepared with routine H&E staining (shown in the image). Identify the structures indicated by the arrows. (A) Minor salivary gland (B) Sebaceous gland (C) Sublingual gland (D) Submandibular gland 34 35