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Chapter 11 Digestive Tract

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Chapter 11 Digestive Tract Anhui Medical University Chapter 11 Digestive tract Lyu Zhengmei Department of Histology and Embryology, Anhui Medical University Anhui Medical University introdction Digestive tract (DT) and Digestive glands ===Digestive system: Functions of DT: Obtain molecules from ingested food. A protective barrier for the body. Anhui Medical University Functions Oral cavity Ingestion and Initial fragmentation esophagus Conduct food from oral to stomach Stomach Complete fragmentation and initial digestion Duodenum Get enzymes from pancreas and liver Jejunum and Ileum Complete digestion and main absorption Large intestine Absorption of Water and ions Elimination of waste products Anhui Medical University Anhui Medical University Part One Oral Cavity and Related structures Anhui Medical University Oral cavity The oral cavity extend from lips to pharynx. lined by nonkeratinized stratified squamous epi., except the gum and hard palate (keratinized). The wall of the oral cavity is made up of CT, muscles and bone. The oral cavity contains the lips, the teeth, the tongue and salivary glands. Anhui Medical University Papillae CV Foliate Filiform papillae Fungiform papillae Circumvallate Fg papillae FL a). Filiform papillae: The most numerous. Present over entire surface. small and conical in shape. b). Fungiform papillae: resemble mushrooms, a narrow stalk and a dilated upper part. Anhui Medical University c). Circumvallate papillae: The largest papillae. CV is encircled by a deep cleft. The epthelium contains numerous of taste buds. Underlying of the mucosa, there are serous glands CV Foliate Fg FL VE: serous glands(von Ebner’s) Anhui Medical University Taste bud 10,000 TBs in your mouth, present in the epi. of fungiform papillae, circumvallate papillae, etc. a onion-shaped structure made up of modified epithelial cells. a small cavity that opens to the surface through a taste pore. The cells in TB are of 3 basic types. Receptor cells or taste cells, supporting cells, which have microvilli on the tip of the cells and basal cells. Anhui Medical University The same taste bud can respond to 4 types of taste (sweet, sour, salty and bitter). The sweet and salty is less sensitive, but bitter is most sensitive. Anhui Medical University Part two Esophagus, Stomach and Intestine Anhui Medical University 1. Components of digestive tract mucosa submucosa muscularis share a similar histological plan: a hollow tube composed of a lumen surrounded by a wall. The wall includes: mucosa, submucosa, muscularis and adventitia. Anhui Medical University 2. General structural details of the wall 1) Mucosa (mucous membrane) ---------Three sublayers Epithelium : stratified squamous epi. simple columnar epi. FUNCTION: A selectively permeable barrier. • Facilitate the transport and digestion. • Promote the absorption •Produce the hormone •Secret mucus for lubrication and protection. Anhui Medical University Lamina propria: LCT rich in BV, LV and LP nerves ,lymphoid tissues, glands Muscularis mucosae : Except esophagus, 2 sublayers (Inner circular and outer longitudinal of smooth muscle). Function: Promote the movements LP of the mucosa and increase its contact with the food. Anhui Medical University 2) Submucosa: CT . Submucosa nerve plexus. 3) Muscularis : Smooth muscle cells and less skeletal muscle cells. inner circular and outer longitudinal sublayer Myenteric nerve plexus mucosa Function: The contraction of muscularis propel and mix the food in digestive tracts. 4) Adventitia submucosa Serosa: LCT + mesothelium Fibrosa: LCT muscularis Anhui Medical University Part 3 Esophagus 1) Mucosa: stratified squamous epi lamina propria muscularis mucosa: only a layer of longitudinal arranged SM 2) Submucosa: CT esophageal gland: mucous gland Anhui Medical University 3) Muscularis: inner circular and outer longitudinal upper portion: only skeletal muscle middle portion: mixture of skeletal and smooth muscle lower end: only smooth muscle 4) Adventitia: fibrosa Functions: Transport food from the mouth to the stomach. Anhui Medical University Stomach Functions: store food temporarily initial digestion absorb part of water and ion Structures: Gross inspection reveals 4 regions: fundus, cardia, body, pylorus Folds or rugae. Anhui Medical University The wall is composed of 4 layers: Mucosa, submucosa, muscularis adventitia. Mucosa have some special features . Mucosa muscularis Anhui Medical University Regions of the stomach and their histological structure Anhui Medical University I. Mucosa of stomach ① Epithelium: Gastric pit Surface mucous cell: Structures: LM: Tall columnar, ovoid and basally- located nucleus. with mucin granules, so cells look empty with HE staining. gastric pit: formed by epithelium invaginates into lamina propria Functions: Secreting mucus, which form mucous barrier Anhui Medical University ② lamina propria: Gastric pit Deep to gastric pits, packed with gastric glands and scanty CT. Here’re 3 types of gastric gland: Main gastric gland cardiac gland pyloric gland. muscularis mucosa Anhui Medical University Main gastric glands Distribution: Most of the stomach (present in the body and fundus) except pylorus and cardia. Structures: Simple or branched tubular glands. The glands open into gastric pits. The epithelium of the glands includes chief cells, parietal cells, neck mucous cells, undifferentiated cells and endocrine cells. Their distribution is not uniform. Anhui Medical University 1. Parietal cell or oxyntic cell Distribution: more numerous in the upper half of the gland. Structures: LM: rounded or pyramidal with round and centrally-located nucleus. The cytoplasm is strongly acidophilic. Anhui Medical University EM: Active cell Intracellular canaliculus (IC), which bear microvilli in the wall. Tubulovesicles (TV) and Abundant Resting cell Mitochondria Functions: secrete hydrochloric acid and produce intrinsic factor. Anhui Medical University Active ce Resting cell EM of Parietal cell Anhui Medical University 1 Function of Hydrochloric acids Pepsinogen (chief cells) hydrochloric acids Proteins Pepsin pH0.9-1.5 Peptides 2 Function of intrinsic factor Intrinsic factor Complex production of erythrocytes Vitamin B12 Anhui Medical University Gastric ulcer Anhui Medical University 2. Chief cell, zymogenic cell Distribution: numerous in the basal part of the glands. Structures: LM: Low columnar, A round and basally-located nucleus. Basal cytoplasm is basophilic and apical is light-stained Anhui Medical University EM: RER, Golgi apparatus and apical granules (pepsinogen). Functions: secrete pepsinogen Pepsin can break down proteins into peptides and solid food become liquefied. Highly active Inactive HCl pepsinogen pepsin digest proteins Anhui Medical University 3. Mucous neck cell Distribution: neck part of the gland. Structures: Columnar cells, A flattened and basally-located Nucleus The cytoplasm is pale-stained in HE stain. Functions: mucus secretion. 4. undifferentiated cell : can multiply to replace other cells and play an important role in healing. 5. Endocrine cell: Anhui Medical University Cardiac glands and pyloric glands Distribution: The mucosa of cardia and pylorus respectively. Function: Mucous secreting glands. Structure: The majority of cells is mucous cells. Occasionally, parietal cells, chief cells and endocrine cells is present. Anhui Medical University ③ muscularis mucosa: 2 sublayers of SM: inner circular and outer longitudinal other layers of stomach Muscularis is well developed ------three sublayers: oblique, circular and longitudinal serosa Anhui Medical University Small intestines Components: Small intestine is a tube, 5 meters long. It is composed of 3 parts: Duodenum: 25 cm long Jejunum: 2 meters long Ileum: 3 meters long Functions: The small intestine is the site of terminal food digestion, nutrient absorption and endocrine secretion. The nutrients are absorbed by the epithelial cells. Anhui Medical University General Structure: The wall of the small intestine includes 4 layers: Serosa similar to other segments Muscularis Submucosa: Mucosa exhibit several special features, will be described below. Mucosa Lamina propria Submucosa Muscularis Anhui Medical University Mucosa The surface area is 600-fold(200m2) increased. Three special fetures as following: 1.Plicae circulares(3-fold) →2. Villi(10-fold)→3. Microvilli(20-fold) Gross inspection Anhui Medical University 1. Plicae circulares (Circular folds) Structure : Mucosa and part of submucosa project into the lumen, which is so large that be readily seen with naked eye. Distribution: most develped in the jejunum. Become fewer and less in the ileum. Function: increase the surface area and slow down the passage of the contents to facilitate absorption. Gross inspection Tissue section Anhui Medical University 2.Intestinal Villi: Structure: finger like projections, 0.5-1.5mm long ,consisting of a core of connective tissue covered by a surface epithelium . The CT core contains 3 important structures: Numerous fenestrated Cap., which allow rapid absorption of nutrients into the blood. A central lymphatic Cap. called a central lacteal. Distal ends blindly and proximal ends in a plexus of lymphatic V. Some smooth muscle cells Anhui Medical University intestinal villi under SEM intestinal villi under LM Distribution: most developed in the duodenum, decrease along SI. Function : villi can increase the surface areas 10-fold. Anhui Medical University 3. intestinal glands(Crypts): The invagination of epithelium into lamina propria. Really simple
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