Digestive System 1: Oral Cavity PDF

Digestive system 1 Oral cavity DR Fatma Meligy The digestive system The digestive system comprises the oral region and alimentary canal (esophagus, stomach and small and large intestines) and several extrinsic glands. Function: Obtain molecules from the ingested food that are necessary for the maint...

Digestive system 1 Oral cavity DR Fatma Meligy The digestive system The digestive system comprises the oral region and alimentary canal (esophagus, stomach and small and large intestines) and several extrinsic glands. Function: Obtain molecules from the ingested food that are necessary for the maintenance, growth, and energy Through ingestion, mastication, digestion and absorption of nutrients and in the elimination of indigestible materials. These functions occurred by help of some enzymes and hormones. Oral cavity The oral region includes the lips; palate; teeth and associated structures; tongue; major salivary glands; and lingual, palatine, and pharyngeal tonsils to protect the entryways into the alimentary canal and the respiratory system. The oral region is lined in The epithelium and most places by a stratified connective tissue together squamous epithelium. The form the mucosa underlying C.T. is formed of dense irregular collagenous C.T lamina propria. The oral cavity has three types of mucosae Lining mucosa: whose epithelium is nonkeratinized; soft palate, inner surface of lips, cheeks, and the floor of the mouth Masticatory mucosa: whose epithelium is keratinized; gingiva (gum), hard palate. and dorsal surface of the tongue (variable degree of keratinization.(protect surfaces exposed to abrasions or forces of mastication) Specialized mucosa, restricted to areas containing taste buds e.g. the dorsum of the tongue The Lips The lips have 3 surfaces; ▪outer (cutaneous). ▪Red (vermilion). ▪inner (oral mucosa The Lips The outer surface ( thin skin ) it consists of an epidermis and an underlying dermis with hair follicles, sebaceous and sweat glands. The inner surface (oral mucosa) is lined by a wet stratified squamous non-keratinized epithelium and many minor labial salivary glands In vermilion zone ( red margin): modified thin skin ▪ Thin epidermis ▪ lightly keratinized. ▪ lacks salivary or sweat glands and is kept moist with saliva from the tongue. Deep dermal papillae is very rich in both sensory innervation and blood capillaries, which cause the pink color and great sensation Core of The Lips Is formed of bundles of striated muscles. A dense irregular collagenous connective tissue core envelops striated muscle. This welldeveloped core of striated muscle in the lips, makes these structures highly mobile for ingestion, speech, and other forms of communication Minor salivary glands are also found near the inner surface which produce mucous important for lubrication minor labial salivary glands Tongue A mass of striated muscle covered by a mucous membrane whose structure varies according to the region. Functions of tongue: 1- Food manipulation 2- Sensory perception (taste) 3- speech The main bulk of the tongue I has dorsal and ventral surfaces between them is the main bulk The ventral surface is covered by non-keratinized stratified squamous epithelium loosely attached to lamina propria Its dorsal surface is covered by stratified squamous epithelium with variable degrees of keratinization. Tongue The dorsal surface has v-shaped groove (sulcus terminalis) that points posteriorly. This sulcus divides the dorsal surface into an anterior 2/3 and a posterior 1/3 The anterior 2/3 is irregular, covered anteriorly by a great number of small eminences called papillae The posterior 1/3 surface shows the many bulges of the lingual tonsils and smaller collections of lymphoid nodules Lingual papillae They are Small projections (elevations) of the mucous membrane of the tongue ( epithelium and connective tissue) Filiform papillae: Most numerous Tall, narrow, conical shape highly keratinized structures Give rough surface for movement of food Lacking taste buds. Fungiform papillae Mushroom-shaped structures Covered by non-keratinized squamous epithelium Interspersed in the tip and sides Have taste buds. Fungiform Circumvallate papillae called vallate papillae Arranged in a single row, which contains about 10 to 14 papillae that are located immediately anterior to the sulcus terminalis Cylindrical in shape and is surrounded by a groove called a moat. Ducts of the glands of von Ebner (minor serous salivary glands) open and drain serous products into the groove; this helps to clear the food debris in the groove and helps in detection of taste Foliate papillae Poorly developed in adults Consist of parallel ridges and furrows located on the posterior lateral surface of the tongue Contain taste buds Taste buds Consist of: Gustatory (taste) cells (light cells) slender supportive cells (dark and intermediate cells), and basal stem cells. The base of each bud rests on the basal lamina perforated by afferent sensory axons that form synapses on the gustatory cells. At the apical ends of the gustatory cells microvilli project through an opening called the taste pore Molecules (tastants) dissolved in saliva contact the microvilli through the pore and interact with cell surface taste receptors Lingual papillae and taste buds Core of the tongue The tongue is a mass of striated muscle covered by mucosa, which manipulates ingested material during mastication and swallowing. The muscle fibers are oriented in all directions, allowing a high level of mobility. Connective tissue between the fascicles of muscle is penetrated by the lamina propria, which makes the mucous membrane strongly adherent to the muscular core. In addition to minor salivary glands. Posterior third of the tongue Covered by stratified squamous epithelium Underneath the epithelium, there is a lymphoid tissue containing lymphoid follicles (lingual tonsils) Epithelial crypts penetrate the lymphoid tissue