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Digestive System Introduction Introduction Introduction 5/14/2016 Introduction • Every cell requires a constant energy source Digestive System – Ingested food is complex • Modification is needed to utilize Introduction Parotid gland Mouth (oral cavity) • Sublingual gland Salivary Digestive system is a tube Tongue Submandibular glands – Gastrointestinal tract gland • Specialized regions Pharynx – Esophagus Mouth Stomach – Pharynx Pancreas (Spleen) – Esophagus Liver Gallbladder – Stomach Transverse colon – Small intestine Duodenum Descending colon – Large intestine Small Jejunum Ascending colon intestine Ileum Cecum Large Sigmoid colon intestine Rectum Vermiform appendix Anus Anal canal Figure 23.1 Introduction Ingestion Food Mechanical digestion Pharynx • • Chewing (mouth) Esophagus Digestive processes • Churning (stomach) Propulsion • Segmentation • Swallowing 1. Ingestion (small intestine) (oropharynx) Chemical • Peristalsis digestion Stomach (esophagus, 2. Propulsion stomach, small intestine, 3. Mechanical digestion large intestine) Absorption 4. Chemical digestion Lymph vessel 5. Absorption Small intestine 6. Defecation Large Blood intestine vessel Mainly H 2O Feces Defecation Anus Figure 23.2 1 5/14/2016 Intrinsic nerve plexuses Introduction • Myenteric nerve plexus • Submucosal nerve plexus Glands in submucosa • Histology of the alimentary canal Mucosa – • Epithelium Four basic layers (tunics) • Lamina propria • Tunica mucosa – innermost layer • Muscularis mucosae – Protection and absorption Submucosa – Epithelium and connective tissue Muscularis • Tunica submucosa externa • Longitudinal – Connective tissue muscle – Binds tube together • Circular muscle Serosa • Nerve Tunica muscularis (externa) • Epithelium – Artery Double layer of muscle Vein • Connective • Tunica serosa tissue Gland in mucosa Lumen – Single layer of epithelium and connective tissue Lymphatic Duct of gland outside Mucosa-associated – Forms the visceral peritoneum Mesentery vessel alimentary canal lymphoid tissue Figure 23.6 Introduction • Peritoneum – Membrane that lines abdominal cavity – Serous membrane – remember, that means 2 layers! • Parietal peritoneum = outer layer (attached to abdominal wall) • Visceral peritoneum = inner layer (wrapped around visceral organs) • Space in between = peritoneal cavity Introduction Introduction • Mesentery • Omenta – Folds in the peritoneum – Folds in peritoneum – – Lesser Attached to intestinal tract Connect stomach to another organ omentum – Encapsulate blood vessels, nerves, fat stores that • Examples: supply the intestine – Lesser omentum connects stomach to liver – Greater omentum connects stomach to colon 2 5/14/2016 Peritoneum Liver Abdominopelvic Lesser omentum cavity Pancreas Vertebra Stomach Transverse mesocolon Dorsal mesentery Duodenum Transverse colon Mesentery Parietal peritoneum Ventral Greater omentum mesentery Visceral Jejunum peritoneum Ileum Visceral peritoneum Peritoneal Alimentary Liver cavity canal organ Parietal peritoneum (a) Schematic cross sections of abdominal cavity Urinary bladder illustrate the peritoneums and mesenteries. Rectum (d) Figure 23.5a Figure 23.30d Digestive System Soft palate Palatoglossal arch Uvula Hard palate • Mouth Oral cavity – Cheek, palate, Palatine tonsil tongue Tongue Oropharynx – Opens into Lingual tonsil oropharynx Epiglottis – Salivary glands Hyoid bone Laryngopharynx Esophagus Trachea (a) Sagittal section of the oral cavity and pharynx Figure 23.7a Salivary glands secrete about 1250 ml of saliva per day! Digestive System Tongue • Teeth Teeth – Held in place by periodontal ligaments Parotid Ducts of gland sublingual – Gingiva covers bone gland Parotid duct Masseter muscle Frenulum – 2 dentitions of tongue Body of Sublingual mandible (cut) • gland Posterior belly Deciduous Mylohyoid of digastric • Permanent muscle (cut) muscle Submandibular Anterior belly of Submandibular duct digastric muscle gland Mucous Serous cells (a) cells forming demilunes (b) Figure 23.9 3 5/14/2016 Teeth 20 deciduous 32 permanent Digestive System Incisors Incisors Central (6–8 mo) Central (7 yr) Lateral (8 yr) • Teeth Lateral (8–10 mo) Canine (eyetooth) Canine (eyetooth) (11 yr) – Anatomy (16–20 mo) Premolars • Molars (bicuspids) Crown First molar First premolar – Covered by enamel (10–15 mo) Deciduous (11 yr) Second molar (milk) teeth Second premolar • Dentin (about 2 yr) (12–13 yr) Molars • Pulp cavity First molar (6–7 yr) • Roots Second molar (12–13 yr) – Function Third molar Permanent (wisdom tooth) • (a) teeth Break down food (17–25 yr) • Mixed with saliva to form bolus Figure 23.10a Enamel Digestive System Dentin Crown Dentinal tubules Pulp cavity (contains Esophagus blood vessels and Pharynx to stomach Neck nerves) Moves bolus to stomach Gingiva (gum) Peristalsis Cardiac (gastroesophageal) sphincter Cementum Heartburn Root canal Histology Root Periodontal Mucosa ligament Stratified squamous epithelium Abundant mucous glands Serosa Apical foramen Entirely connective tissue Bone Figure 23.11 Relaxed muscles 4 Food is moved through Circular muscles the esophagus to the stomach by peristalsis. Parotid gland contract Mouth (oral cavity) Sublingual gland Salivary Tongue Submandibular Bolus of food glands gland Longitudinal muscles contract Esophagus Pharynx Stomach Pancreas Liver (Spleen) Gallbladder Gastroesophageal sphincter closed Transverse colon Duodenum Descending colon Small Jejunum Ascending colon intestine Ileum Cecum Large Stomach Sigmoid colon intestine Rectum Vermiform appendix Anus Anal canal Figure 23.1 Figure 23.13, step 4 4 5/14/2016 Relaxed 5 The gastroesophageal muscles sphincter opens, and food enters the stomach. Mucosa (contains a stratified squamous epithelium) Submucosa (areolar connective tissue) Lumen Gastroesophageal Muscularis externa sphincter opens • Longitudinal layer • Circular layer Adventitia (fibrous connective tissue) (a) Figure 23.13, step 5 Figure 23.12a Cardia simple columnar Fundus epithelium Esophagus Muscularis externa Serosa • Longitudinal layer • Circular layer Body • Oblique layer Lumen Mucosa Lesser (contains a stratified curvature Rugae of squamous epithelium) mucosa Esophagus stomach junction Greater curvature Pyloric Pyloric Duodenum canal antrum Pyloric sphincter (b) (a) (valve) at pylorus Figure 23.12b Figure 23.14a Digestive System Falciform ligament Liver Gallbladder • Stomach Spleen – From cardiac orifice to pyloric sphincter Stomach • Rugae (flatten as stomach fills) – Greater curvature Ligamentum teres • Convex lateral surface Greater omentum • Greater omentum Small intestine – Lesser curvature • Concave medial surface Cecum • Lesser omentum (a) Figure 23.30a 5 5/14/2016 Digestive System Liver Gallbladder Lesser omentum • Stomach – Stomach Four tunics Duodenum • Muscularis – Additional layer of muscle in an oblique orientation Transverse colon – Three layers of smooth muscle Small intestine Cecum Urinary bladder (b) Figure 23.30b Cardia Fundus Digestive System Esophagus Muscularis externa Serosa • • Longitudinal layer Stomach • Circular layer Body – Four tunics • Oblique layer • Lesser Lumen Mucosa curvature Rugae of – Gastric glands mucosa » Mucous cells = Mucous » Parietal cells = Intrinsic factor and HCl » Greater Zymogenic (chief) cells = Pepsinogen » curvature Enteroendocrine cells = Gastrin and cholecystokinin Pyloric Pyloric Duodenum canal antrum Pyloric sphincter (a) (valve) at pylorus Figure 23.14a Gastric pits Surface epithelium Surface epithelium (mucous cells) Mucosa Gastric pit Mucous neck cells Mucosa contains gastric glands Lamina propria Parietal cell Chief cell Muscularis mucosae Gastric Submucosa gland (contains submucosal plexus) Oblique layer Muscularis externa Circular layer (contains myenteric Longitudinal plexus) layer Serosa Stomach wall Enteroendocrine cell (a) Layers of the stomach wall (l.s.) (b) Enlarged view of gastric pits and gastric glands Figure 23.15a Figure 23.15b 6 5/14/2016 Pepsinogen Pepsin Digestive System HCl • Chemical digestion in the stomach Mitochondria – Protein catabolism → polypeptides Parietal cell – Secretions HCl • Pepsinogen → pepsin • HCl – Chief (Zymogenic) cell pH 1.5–3.5 – Denatures protein in food – Kills many bacteria Enteroendocrine cell • Intrinsic factor – (c) Location of the HCl-producing parietal cells and Required for absorption of vitamin B 12 in small intestine pepsin-secreting chief cells in a gastric gland Figure 23.15c Digestive System Digestive System • Chemical digestion in the stomach • Chemical digestion in the stomach – Enteroendocrine cells – Chyme • Secrete hormone-like substances • – Gastrin Product of stomach digestion » Stimulates parietal cells to release HCl – Prevention of autodigestion » Increases gastric motility, emptying • – Cholecystokinin Mucous » Primarily produced by enteroendocrine cells in the • Gastritis duodenum • Peptic ulcers » Inhibits HCl release and gastric emptying – » Stimulates pancreas to release digestive enzymes Gastric ulcers » Stimulates production and release of bile from gall bladder – Duodenal ulcers » Contributes to feelings of satiety after eating Digestive System Digestive System • Control of gastric secretions • Control of gastric secretions – Neural control – Hormonal control • Seeing, smelling, tasting, thinking about food stimulates • Gastrin gastric secretions via the vagus nerve – Released reflexively by enteroendocrine cells in • Enteric nervous system provides local control independently of brain and spinal cord response to stomach distension, peptides, and low acidity – Spinal cord injury will not damage! – – Ischemia can damage, but transplants
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