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The Digestive System Overview of the Digestive System • Organs Are Divided Into Two Groups the Alimentary Canal and Accessory

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C H A P T E R 23 The Digestive System 1 Overview of the Digestive System • Organs are divided into two groups • The alimentary canal • Mouth, pharynx, and esophagus • Stomach, small intestine, and large intestine (colon) • Accessory digestive organs • Teeth and tongue • Gallbladder, salivary glands, liver, and pancreas 2 The Alimentary Canal and Accessory Digestive Organs Mouth (oral cavity) Parotid gland Tongue Sublingual gland Salivary glands Submandibular gland Esophagus Pharynx Stomach Pancreas (Spleen) Liver Gallbladder Transverse colon Duodenum Descending colon Small intestine Jejunum Ascending colon Ileum Cecum Large intestine Sigmoid colon Rectum Anus Vermiform appendix Anal canal Figure 23.1 3 1 Digestive Processes • Ingestion • Propulsion • Mechanical digestion • Chemical digestion • Absorption • Defecation 4 Peristalsis • Major means of propulsion • Adjacent segments of the alimentary canal relax and contract Figure 23.3a 5 Segmentation • Rhythmic local contractions of the intestine • Mixes food with digestive juices Figure 23.3b 6 2 The Peritoneal Cavity and Peritoneum • Peritoneum – a serous membrane • Visceral peritoneum – surrounds digestive organs • Parietal peritoneum – lines the body wall • Peritoneal cavity – a slit-like potential space Falciform Anterior Visceral ligament peritoneum Liver Peritoneal cavity (with serous fluid) Stomach Parietal peritoneum Kidney (retroperitoneal) Wall of Posterior body trunk Figure 23.5 7 Mesenteries • Lesser omentum attaches to lesser curvature of stomach Liver Gallbladder Lesser omentum Stomach Duodenum Transverse colon Small intestine Cecum Urinary bladder (b) Figure 23.6b 8 Mesenteries • Greater omentum— Greater omentum a “fatty apron” of Transverse colon peritoneum Transverse • Greater omentum and mesocolon Descending colon transverse colon Jejunum reflected Mesentery Sigmoid mesocolon Sigmoid colon Ileum (c) Figure 23.6c 9 3 Mesenteries • Sagittal section through Liver the abdominopelvic Lesser omentum Pancreas cavity Stomach Duodenum Transverse • Mesenteries attach to mesocolon Transverse colon posterior abdominal wall Mesentery Greater omentum Jejunum Ileum Visceral peritoneum Parietal peritoneum Urinary bladder Rectum (d) Figure 23.6d 10 Histology of the Alimentary Canal Wall • Same four layers from esophagus to anus • The mucosa – innermost layer • Consists of: • Epithelium • Lamina propria • Muscularis mucosae • The submucosa – external to the mucosa • Contains blood and lymphatic vessels, nerve fibers • The muscularis externa – external to the submucosa • Two layers • Circular muscularis • Longitudinal muscularis • The serosa – the outermost layer • The visceral peritoneum • Nerve plexuses • Myenteric nerve plexus • Submucosal nerve plexus 11 Histology of the Alimentary Canal Intrinsic nerve plexuses Myenteric nerve plexus Submucosal nerve plexus Glands in submucosa Mucosa Epithelium Lamina propria Muscularis mucosae Submucosa Muscularis externa Longitudinal muscle Circular muscle Serosa Epithelium Connective tissue Nerve Artery Gland in mucosa Lumen Vein Duct of gland outside Mucosa-associated Mesentery Lymphatic vessel alimentary canal lymphoid tissue (a) Longitudinal and cross-sectional views through the small intestine Figure 23.7a 12 4 Histology of the Alimentary Canal Mucosa Submucosa Muscularis externa Serosa (b) Light micrograph cross section through the small intestine (30×) Figure 23.7b 13 Smooth Muscle Longitudinal layer of smooth muscle (shows smooth muscle fibers in cross section, 145×) Small intestine Mucosa (a) Location and plane of (b) Cross section of the intestine Circular layer of smooth section shown in (b) showing the smooth muscle muscle (shows longitudinal layers (one circular and the views of smooth muscle other longitudinal) running fibers, 145×) at right angles to each other Figure 23.8a, b 14 The Mouth and Associated Organs • The mouth – oral cavity • Mucosal layer • Stratified squamous epithelium • Lamina propria • The lips and cheeks • Formed from orbicularis oris and buccinator muscles, respectively 15 5 Anatomy of the Mouth Soft palate Palatoglossal arch Uvula Hard palate Oral cavity Palatine tonsil Tongue Oropharynx Lingual tonsil Epiglottis Hyoid bone Laryngopharynx Esophagus Trachea (a) Sagittal section of the oral cavity and pharynx Figure 23.11a 16 Anatomy of the Mouth • The labial frenulum • Connects lips to gum Upper lip • The palate Gingivae (gums) Superior labial frenulum • Forms the roof Palatine raphe Palatoglossal of the mouth Hard palate arch Soft palate Palatopharyngeal arch Uvula Palatine Posterior wall tonsil of oropharynx Tongue Sublingual Lingual frenulum fold with Opening of openings of submandibular sublingual duct ducts Gingivae (gums) Vestibule Inferior labial Lower lip frenulum (b) Anterior view Figure 23.11b 17 The Tongue • Interlacing fascicles of skeletal muscle • Grips food and repositions it • Helps form some consonants • Intrinsic muscles – within the tongue • Extrinsic muscles – external to the tongue 18 6 The Superior Surface of the Tongue • Tongue papillae • Filiform papillae • Fungiform papillae • Vallate papillae Figure 23.12 19 The Teeth • Dentition and dental formula • Deciduous teeth – 20 teeth • First appear at 6 months of age • Permanent teeth – 32 teeth • Most erupt by the end of adolescence • Dental formula – shorthand • Way to indicate number and position of teeth 20 The Teeth Incisors Central (7 yr) Lateral (8 yr) Canine (eyetooth) (11 yr) Premolars (bicuspids) First premolar (11 yr) Incisors Second premolar Central (6–8 mo) (12–13 yr) Lateral (8–10 mo) Molars Canine (eyetooth) First molar (16–20 mo) (6–7 yr) Molars Second molar First molar (12–13 yr) (10–15 mo) Deciduous Third molar Permanent Second molar (milk) teeth (wisdom tooth) teeth (about 2 yr) (17–25 yr) (a) Figure 23.13a 21 7 The Teeth Deciduous teeth Permanent teeth (b) Figure 23.13b 22 Tooth Structure Enamel Longitudinal Dentin • Crown Dentinal tubules section of tooth in Pulp cavity (contains alveolus blood vessels Neck and nerves) Gingiva (gum) Cementum Root canal Root Periodontal ligament Apical foramen Bone Figure 23.14 23 The Salivary Glands Tongue Teeth Parotid gland Ducts of sublingual Parotid duct gland Masseter muscle Frenulum of tongue Body of mandible (cut) Sublingual gland Posterior belly of digastric muscle Mylohyoid Submandibular muscle (cut) duct Anterior belly of Submandibular digastric muscle gland Mucous cells Serous cells forming (a) (b) demilunes Figure 23.15 24 8 The Pharynx • Oropharynx and laryngopharynx – passages for air and food • Lined with stratified squamous epithelium • External muscle layer • Consists of superior, middle, and inferior pharyngeal constrictors 25 The Esophagus • Gross anatomy – muscular tube • Begins as a continuation of the pharynx • Joins the stomach inferior to the diaphragm • Microscopic anatomy • Epithelium is stratified squamous epithelium • When empty – mucosa and submucosa in longitudinal folds • Mucous glands – primarily compound tubuloalveolar glands • Muscularis externa – skeletal muscle first third of length • Most external layer – adventitia 26 Microscopic Structure of the Esophagus Mucosa (contains a stratified squamous epithelium) Submucosa (areolar connective tissue) Lumen Muscularis externa Circular layer Longitudinal layer Adventitia (fibrous connective tissue) (a) Cross section through esophagus (5×) (b) Gastroesophageal junction, longitudinal section (85×) Figure 23.16 27 9 The Stomach • Site where food is churned into chyme • Protein digestion begins • Secretes pepsin • Functions under acidic conditions 28 The Stomach Cardia Fundus Esophagus Muscularis externa Serosa Longitudinal layer Circular layer Oblique layer Body Lumen Lesser curvature Rugae of mucosa Greater curvature Pyloric Pyloric Duodenum canal antrum Pyloric sphincter (a) (valve) at pylorus Figure 23.17a 29 The Stomach—Microscopic Anatomy Gastric pits Surface epithelium (mucous cells) Surface Gastric epithelium pit Mucous neck cells Mucosa Parietal cell Lamina Gastric propria gland Muscularis mucosae Submucosa (contains Chief cell submucosal plexus) Oblique layer Muscularis externa Circular layer (contains myenteric Longitudinal plexus) layer Enteroendocrine cell Serosa Stomach wall (b) Enlarged view of gastric pits and gastric glands (a) Layers of the stomach wall, longitudinal section Pepsinogen Pepsin Mucus-secreting HCl cells Gastric pits Surface mucous cell Mitochondria Mucus neck cells Parietal cell HCl secreting parietal cells Gastric gland Chief cell Enzyme secreting chief cells Enteroendocrine cell Muscularis mucosae (c) Location of the HCl-producing parietal cells and (d) Micrograph of the stomach mucosa, view similar to part (b) (115×) pepsin-secreting chief cells in a gastric gland Figure 23.18 30 10 The Small Intestine – Gross Anatomy • Longest portion of the alimentary canal • Site of most enzymatic digestion and absorption • Three subdivisions • Duodenum • Brunner’s glands • Jejunum • Ileum • Peyer’s patches 31 The Small Intestine—Structural Features Vein carrying blood to hepatic portal vessel Muscle layers Lumen Circular Microvilli folds (brush Absorptive border) Villi cells Lacteal Goblet cell Blood Absorptive cells capillaries Vilus (a) Mucosa Goblet associated cells lymphoid Villi tissue Intestinal Enteroendocrine crypt cells Muscularis Venule mucosae Lymphatic vessel Duodenal (b) gland Submucosa (c) Intestinal crypt Figure 23.20 32 The Duodenum • Receives digestive enzymes and bile • Main pancreatic duct and common bile duct enter duodenum • Sphincters control entry of bile
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