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Gastrointestinal Tract 1. Gastrointestinal Tract(oral cavity till anal orifice). 2. Assosciated Glands. Oral Cavity Within the oral cavity are the tongue, teeth and the salivary glands ,which empty their secretory products into the oral cavity. Histology of GIT Schematic diagram showing different layers of GIT 1. Mucosa Submucosa Muscularis Serosa 2. 3. 4. Mucosa Consists of: Lining epithelium made of simple columnar epithelium It sits on a basement membrane Lamina propria made of loose connective tissue bfull of macrophges and lymphocytes Muscularis mucosae separate mucosa from submucosa contraction of which leads to increase contact of epithelium with food Sumucosa Consists of a layer of dense connective tissue Rich in blood vessels Contains submucosal nerve plexuses Some times it may contain mucus glands Muscularis Generally, it consists of two layers of smooth muscle fibers Inner circular and outer longitudinal Myenteric nerve plexuses are distributed between the two muscle layers With the submucosal nerve plexuses, they help propel and mixing the food Serosa It is a layer of loose connective tissue covered by a layer of simple squamous epithelium called mesothelium It contains the lymphatic and blood vessels of the GI tract and fat tissue Functions of the GIT Selective permeability Transport and food digestion Absorption of food Secretion of hormones and enzymes of digestion Production of mucus for lubrication and moisturizing ingested food Immunity The epithelial lining is divided into two types: 1.Masticatory epithelium covers (tongue, gingivae and hard palate). The epithelium is keratinized stratified squamous epithelium. 2.Lining epithelium, i.e. nonkeratinised stratified squamous epithelium, covers the remaining surfaces of the oral cavity. Oral cavity Is lined with stratified squamous epithelium to protect the mouth from the effect of food Soft palate, floor of the mouth, lips, and cheeks are lined with nonkeratinized epithelium Lamina propria contains many diffuse salivary glands The Tongue It consists of skeletal muscle fibers concerned with change in tongue shape The tongue is attaches to nearby bony structures to move the tongue in various directions It is covered by different types of papillae Tongue Papillae They are four types: Filliform Fungiform Circumvallate Foliate With the exception of filiform, they contain taste buds for taste sensation Taste bud consists of sensory cells, supporting cells, and basal cells Von Ebner glands Lingual Papilla Papillae are elevations of the oral epithelium and lamina propria that assume various forms and functions. Filiform papillae have an elongated conical shape; they are quite numerous and are present over the entire surface of the tongue. Their epithelium, which does not contain taste buds, is keratinized. Fungiform papillae resemble mushrooms.These papillae, which contain scattered taste buds on their upper surfaces, are irregularly interspersed among the filiform papillae. Foliate papillae are poorly developed in humans. They consist of two or more parallel ridges and furrows on the dorsolateral surface of the tongue and contain many taste buds. Circumvallate papillae are 7–12 extremely large circular papillae whose flattened surfaces extend above the other papillae. They are distributed in the V region in the posterior portion of the tongue. Numerous serous (von Ebner's) glands drain their contents into the deep groove that encircles the periphery of each papilla Taste Buds Cells that form the taste bud can functionally be divided into three groups: Sensory cells, Supporting (or sustentacular) cells Basal cells(regenerate the two other cell types) Taste buds are also found in the palate, in the pharynx and larynx. Teeth There are 20 deciduous teeth There are 32 permanent teeth Each tooth consists of : Enamel (ameloblasts) Dentin(odontoblasts) Pulp Cementum(cementocytes Periodontal ligament Root canal Gingiva Histology of GIT Eosophagus Consists of four layers Lining epithelium is stratified squamous non-keratinized Eosophageal submucus gland Eosopageal cardiac glands Muscular layer Covering serosa and adventitia Parts of the esophagus Upper part Middle part Lower part Stomach It is a mixed gland and secretes hormones Is divided histologically into three parts: Body and fundus: secrete HCL Cardia: secretes mucus Pyloric region: secretes mucus Mucosa and submucosa are found within rugae Muscularis consists of three layaers Cardia contains simple or branched tubular glands Stomach Cont. Fundus and body contain branched tubular glands 3-7 opens into one pit Gastric gland is divided into: Gastric pit Isthmus Neck Base Stomach Cont. Gastric gland contains the following cells: Surface mucus Stem cells Mucus neck cells : mucus Parietal (Oxyntic cells) : HCL Chief cells : pepsinogen Enteroendocrine cells : gastrin and serotonin Regions of the Stomach Transition Zone between Stomach and Duodenum Small Intestine Consists of four layers Mucosa Lining epithelium is simple columnar ,lamina propria containg intestinal glands & muscularis mucosae Submucosa(c.t) In the duodenum there are submucosal glands called Brunner’s glands Muscular layer inner circular and outer longitudinal. Serosa (c.t and mesothelium) Small intestine cont. Is the site of terminal digestion, absorption and enteroendocrine secretion Composed of Duodenum, Jejunum, Ileum Plica circularsis mostly in jejunum composed of mucosa and sumucosa increase the surface area 3 times Intestinal villi leaf-like to tubular form composed of epithelium and lamina propria Intestinal glands (simple tubular) Lined with absorbtive columnar cells and goblet cells Paneth cells M cells M (microfold) cells are specialized epithelial cells overlying the lymphoid follicles of Peyer's patches. These cells are characterized by the presence of intraepithelial lymphocytes and antigen-presenting cells (macrophages). M cells can endocytose antigens and transport them to the underlying macrophages and lymphoid cells, Small Intestine Cont., Intestinal glands (Crypt of Lieberkühn) Are short tubular glands Continuous with intestinal villi Contain enteroendocrine cells and Paneth cells Absorptive epithelium It has many microvilli (brush border) and goblet cells It contains stem cells that replace other types of cells Villi increase the surface area by 10 and microvilli and increase the surface area by 20 time. Regions of Small Intestine Jejunum Ileum and Peyer’s patches Duodenum and Bruner’s glands Between the intestinal villi we see the openings of simple tubular glands, the crypts of Lieberkühn.They extend through the lamina propria down to the muscularis mucosae. Undifferentiated cells close to the bottom of the crypts regenerate the epithelium. Large Intestine No folds or villi Abundance of goblet cells Absorptive cells with irregular microvilli Stem cell in lower portion of the glands Few enteroendocrine cells Lymph follicles Taeniae coli Appendices epiploicae Appendix It is a large intestine Except: Narrow, small, irregular lumen Abundunt lymphoid follicles Few and short glands No teniae coli Medical Application Congenital Pyloric Hypertrophy Atrophic Gastritis Peptic ulcer Malabsorption syndrome Megacolon Appendicitis Thank You a a