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Chapter 25 Digestive system Functions of Digestive system • I. Alimentary canal Mouth anus • 1) Ingestion • 2) Digestion: mechanical & chemical • 3) Move food through- peristalsis • 4) Absorb nutrient molecules • 5) Excretion of waste (food & waste from liver) • 6) Compaction: dehydration of indigestible materials compacted material: feces. Defecation. Figure 25.1 Components of the Digestive System Salivary Glands Oral Cavity, Teeth, Tongue Mechanical processing, moistening, mixing with salivary secretions Secretion of lubricating fluid containing enzymes that break down carbohydrates Mouth Liver Pharynx Secretion of bile (important for lipid digestion), storage of nutrients, many other vital functions Muscular propulsion of materials into the esophagus Esophagus Transport of materials to the stomach Gallbladder Storage and concentration of bile Stomach Pancreas Chemical breakdown of materials via acid and enzymes; mechanical processing through muscular contractions Exocrine cells secrete buffers and digestive enzymes; endocrine cells secrete hormones Large Intestine Small Intestine Dehydration and compaction of indigestible materials in preparation for elimination Enzymatic digestion and absorption of water, organic substrates, vitamins, and ions Anus II. Layers of Alimentary canal A. Mucosa: mucous membrane layer surrounding lumen. 1) epithelium: glandular epithelial cells, secrete digestive juices & goblet cells that secrete mucus. This changes with the location of the digestive tract. Eg) esophagus: stratified squamous ; stomach: simple columnar with goblet cells; small intestine; simple columnar with microvilli & goblet cells; lg intestine: simple columnar with many goblet cells; rectum: upper half is simple columnar, lower half is stratified squamous. 2) lamina propria (loose CT) w/ capillaries to absorb nutrients has MALT 3) muscularis mucosa- thin smooth muscle layer that has small movements eg) twitch to dislodge sharp food. (Cancer diagnosed if cells break this barrier!) B. Submucosa: Dense irregular CT, allows elasticity. Larger blood vessels, lymph & nerve. C. Muscularis externa: most of tract has 2 smooth muscle layers 1) Inner circular layer – segmentation of food 2) Outer longitudinal layer-peristalsis- food moves down length of GI tract D. Serosa: visceral peritoneum, secretes fluid. This last layer is called adventitia for organs that are retroperitoneal. Adventitia is fibrous CT. Figure 25.2a Histological Structure of the Digestive Tract Mesenteric artery and vein Mesentery Plica Mucosa Submucosa Muscularis externa Serosa (visceral peritoneum) a Three-dimensional view of the histological organization of the general digestive tube © 2015 Pearson Education, Inc. Figure 25.2b Histological Structure of the Digestive Tract Plica Mucosal epithelium Lamina propria Mucosa Villi Mucosal glands Submucosal gland Muscularis mucosae Lymphatic vessel Mucosa Artery and vein Submucosa Muscularis externa Serosa (visceral peritoneum) Submucosal plexus Circular muscle layer Myenteric plexus Longitudinal muscle layer An enlarged section of the digestive tube showing the structure of a plica Figure 25.2c Histological Structure of the Digestive Tract Plica (mucosal fold) Villi Muscularis mucosae Mucosa Submucosa Circular muscle layer The ileum LM 180 Longitudinal muscle layer Serosa Photomicrograph of the ileum showing aspects of the histological organization of the small intestine Muscularis externa See peristalsis in gastric antrum (lower part) Figure 25.3 Peristalsis and Segmentation Peristalsis Segmentation INITIAL STATE Longitudinal muscle Circular muscle From mouth To anus Contraction Contraction of circular muscles behind bolus Contraction of longitudinal muscles ahead of bolus Contraction Contraction Contraction in circular muscle layer forces bolus forward Segmentation movements primarily involve the circular Peristalsis propels materials along the length of the digestive tract by coordinated contractions of the circular and longitudinal layers. churn and mix the contents of the digestive tract, but do not produce net movement in a particular direction. muscle layers. III. Peritoneum - The serosa (visceral peritoneum) is continuous with the parietal peritoneum A. Intraperitoneal organs: Organs are surrounded completely by the visceral peritoneum B. Retroperitoneal organs: Organs are covered by the visceral peritoneum on their anterior surface Retroperitoneal organs are: SAD PUCKER S - Suprarenal (adrenal) gland A - aorta/IVC D - duodenum (second and third part) P - pancreas (except tail) U – ureters C - colon (ascending and descending) K – kidneys E – esophagus R – rectum C. Mesenteries: fused double sheets of peritoneal membrane which carry blood vessels to intestines - Omentum: specialized to store fat/ cushion -Greater omentum: greater curvature of stomach over intestines -Lesser omentum: lesser curvature of stomach to liver Figure 25.4b Mesenteries Falciform ligament Diaphragm Liver Lesser omentum Pancreas Duodenum Mesentery proper Stomach Transverse mesocolon Transverse colon Greater omentum Sigmoid mesocolon Rectum Urinary bladder Parietal peritoneum Small intestine Uterus Mesenteries of the abdominopelvic cavity, as seen in a diagrammatic sagittal section Figure 25.10 Anatomy of the Stomach (3 of 5) Mesenteries of the Stomach Lesser curvature (medial surface) Retractor Esophagus Lesser Omentum Diaphragm The lesser omentum lies between the stomach and proximal duodenum and the liver. Fundus Cardia Liver Hepatogastric Ligament STOMACH The hepatogastric ligament connects the liver to the lesser curvature of the stomach. Blood Supply to the Stomach Left gastric artery Hepatoduodenal Ligament The hepatoduodenal ligament connects the liver to the proximal segment of the duodenum. Spleen Body Left gastroepiploic artery Right gastric artery Pylorus Right gastroepiploic artery Greater Omentum The greater omentum forms a large pouch that hangs like an apron from the greater curvature of the stomach. Greater curvature (lateral surface) Gall bladder Duodenum Right kidney Transverse colon © 2015 Pearson Education, Inc. Figure 25.10 Anatomy of the Stomach (4 of 5) Esophagus Diaphragm Left gastric artery Liver, right lobe Liver, left lobe Vagus nerve (N X) Lesser curvature Fundus Hepatic artery Gallbladder Combine bile duct Cardia STOMACH Pyloric sphincter Body Spleen Greater curvature with greater omentum attached Pylorus Greater omentum © 2015 Pearson Education, Inc. IV. Alimentary Canal/ Gastrointestinal tract A. Mouth 1. Tongue: skeletal muscle, lingual frenulum, hyoid bone a) Papillae (contain taste buds. Gustatroy cells (chemorectptors) found within taste buds) 1. filiform - Rough. Most numerous. No taste buds- for mechanical breakdown of food. 2. fungiform- mushroom like, taste buds 3. vallate (circumvallate) large, 10-12 on the posterior 1/3 of tongue Some taste buds also found on hard palate, epiglottis, & pharynx. b) Lingual tonsils: at base of tongue- posterior to vallate papillae c) saliva: amylase, lipase (produced by glands of tongue), histatins : wound healing d) bolus: chewed food mixed with saliva © 2015 Pearson Education, Inc. Tongue Visible fungiform papillae (large bumps) scattered among filiform papillae (small bumps). Filiform are keratinized & appear white. Fungiform papillae are vascularized & appear red. Lingual tonsils • • • • • • • • 2. Teeth. a) Crown i. Enamel: outer layer. No cells, not vascularized. 99% is hypoxyapatite crystals (same calcium salts in bone). Hardest substance in the body! ii. Dentin a yellow, bone-like layer with mineral and collagen. Lacks blood vessels. Has small tubules that lead to pulp. significance? iii. pulp cavity & root canal has blood & nerves. Supplies nutrients for harder tissues. The pulp extends to the root of the tooth, this is called the root canal. b) Neck- gingiva c) Root Cementum: external surface of tooth’s root, attaches tooth to periodontal ligaments, which bind tooth to bony socket in jaw. Figure 25.7a Teeth Enamel Crown Dentine Pulp cavity Gingiva Neck Gingival sulcus Cement Periodontal ligament Root Root canal Bone of alveolus Apical foramen Diagrammatic section through a typical adult tooth Branches of alveolar vessels and nerves Teeth Figure 25.7e Teeth Maxilla exposed to show developing permanent teeth Erupted deciduous teeth First and second molars Mandible exposed to show developing permanent teeth The skull of a 4-year-old child, with the maxillae and mandible cut away to expose the unerupted permanent teeth Figure 25.5a The Oral Cavity Hard palate Soft palate Nasal cavity Palatoglossal arch Opening of parotid duct Upper lip Cheek Dorsum of tongue Lower lip Gingiva Vestibule Body of tongue Root of tongue Pharyngeal tonsil Entrance to auditory tube Nasopharynx Uvula Palatine tonsil Fauces Palatopharyngeal arch Oropharynx Lingual tonsil Epiglottis Hyoid bone Laryngopharynx The oral cavity as seen in sagittal section Swallowing Reflex action. Close of nasopharynx Close off trachea Figure 25.6a The Salivary Glands Openings of sublingual ducts Lingual frenulum Opening of left submandibular duct Sublingual salivary gland Parotid salivary gland Parotid duct Submandibular duct Submandibular salivary gland Lateral view showing the relative positions of the salivary glands and ducts on the left side of the head. Much of the left half of the body and the left ramus of the mandible have been removed. For the positions of the ducts inside the oral cavity, see Figure 25.5. Figure 25.9 Histology of the Esophagus Stratified squamous epithelium Muscularis mucosae Lamina propria Mucosa Submucosa Muscularis externa Muscularis mucosae Adventitia The esophagus a Low-power view of a section through the esophagus © 2015 Pearson Education, Inc. LM x 5 The esophageal mucosa LM x 300 b The esophageal mucosa Figure 25.10 Anatomy of the Stomach (5 of 5) Gastroesophageal junction Regions of the Stomach Fundus Esophagus The fundus is the region of the stomach superior to the junction between the stomach and the esophagus (the gastroesophageal junction). Musculature of the Stomach Longitudinal muscle layer Anterior surface Circular muscle layer Oblique muscle layer (overlying mucosa) Duodenum Pyloric canal Pyloric antrum © 2015 Pearson Education, Inc. The cardia is the superior, medial portion of the stomach within 3 cm of the gastroesophageal junction. Body The body, the largest region of the stomach, is the area between the fundus and the pylorus. Lesser curvature (medial surface) Pyloric sphincter Cardia Pyloris Rugae The pylorus extends to the entrance to the duodenum. It is divided into the pyloric antrum and the pyloric canal. A muscular pyloric sphincter regulates the passage of materials into the duodenum. Greater curvature (lateral surface) Right gastroepiploic vessels Shark stomach showing rugae Figure 25.12c Histology of the Stomach Wall Layers of the Stomach Wall Mucosa Gastric pit (opening to gastric gland) Mucous epithelium Lamina propria Muscularis mucosae Submucosa Muscularis externa Artery and vein Oblique muscle Circular muscle Longitudinal muscle Serosa Lymphatic vessel Myenteric plexus c Diagrammatic view of the organization of the stomach wall. This corresponds to a sectional view through the area indicated by the box in part (b). © 2015 Pearson Education, Inc. Figure 25.12d Histology of the Stomach Wall Luminal surface Lamina propria Gastric pit Mucous neck cells Cells of Gastric Glands Gastric gland Parietal cells G cell Chief cells Smooth muscle cell Muscularis mucosae d Diagrammatic view of a gastric gland and micrograph of the gastric mucosa. © 2015 Pearson Education, Inc. LM x 200 Figure 25.13b Histology of the Stomach Wall Figure 25.13 Regions of the Small Intestine Transverse colon Regions of the Small Intestine Duodenum Jejunum Ileum Ascending colon Cecum Descending colon Sigmoid colon Rectum © 2015 Pearson Education, Inc. Figure 25.15 Regions of the Small Intestine (1 of 4) Jejunum Serosa Duodenum Duodenal submucosal glands Muscularis externa Plicae Submucosa Mucosa Muscularis mucosae Villi Aggregated lymphoid nodules (Peyer’s patches) © 2015 Pearson Education, Inc. Ileum Figure 25.15a Histology of the Intestinal Wall Plica circulares Villi Characteristic features of the intestinal lining Figure 25.14b Histology of the Intestinal Wall Villi Layers of the Small Intestine Mucosa Muscularis mucosae Submucosa Muscularis externa Serosa b The organization of villi and the intestinal crypts © 2015 Pearson Education, Inc. Intestinal crypt Lymphoid nodule Lacteal Submucosal artery and vein Lymphatic vessel Submucosal plexus Circular layer of smooth muscle Myenteric plexus Longitudinal layer of smooth muscle Figure 25.15c Histology of the Intestinal Wall Goblet cell Columnar epithelial cell Lacteal Nerve Capillary network Lamina propria Arteriole Venule Lymphatic vessel Diagrammatic view of a single villus showing the capillary and lymphatic supply Figure 25.16 Regions of the Small Intestine (Part 3 of 4) Figure 25.15d Histology of the Intestinal Wall Villi Mucosa Intestinal crypts Muscularis mucosae Submucosa Vein Artery LM 50 Panoramic view of the wall of the small intestine showing mucosa with characteristic villi, submucosa, and muscularis layers Figure 25.14e Histology of the Intestinal Wall Villus Villi Nuclei of simple columnar epithelial cells Capillary network Goblet cells Lamina propria Brush border (microvilli) LM x 360 e Photomicrographs of villi from the jejunum © 2015 Pearson Education, Inc. LM x 620 Figure 25.17a The Large Intestine TRANSVERSE COLON Aorta Hepatic portal vein Splenic vein Superior mesenteric artery Inferior mesenteric vein Superior mesenteric vein Inferior vena cava Left colic (splenic) flexure Right colic (hepatic) flexure Greater omentum (cut) DESCENDING COLON Left colic vein Middle colic artery and vein Inferior mesenteric artery Left colic artery Right colic artery and vein ASCENDING COLON Omental appendices Ileocecal valve Haustra Intestinal arteries and veins Ileum Rectal artery Cecum Sigmoid arteries and veins Taenia coli Gross anatomy Appendix and regions of the large intestine Sigmoid flexure SIGMOID COLON Rectum Figure 25.17b The Large Intestine Ileal papilla Ileocecal valve Cecum (cut open) Appendix The cecum and appendix Figure 25.18 Anterior/Posterior Radiograph of the Colon Figure 25.19a The Wall of the Large Intestine Taenia coli Omental appendices Haustrum Simple columnar epithelium Goblet cells Intestinal crypt Muscularis mucosae Submucosa Aggregated lymphoid nodule Longitudinal layer Circular (taenia coli) layer Muscularis externa Diagrammatic view of the colon wall Figure 25.18b The Wall of the Large Intestine Simple columnar epithelium Goblet cells Intestinal crypt Muscularis mucosae Submucosa The colon LM x 114 b Colon histology showing detail of mucosal and submucosal layers © 2015 Pearson Education, Inc. Colonoscopy Colon is subject to growth of polyps: small growths from epithelial lining. Can be either benign or cancerous. Images from inside the large intestine during a colonoscopy. In the bottom photo, the doctor is using a tiny tool to remove a polyp. Nat Geo. video on dig. system Accessory Organs Figure 25.19c Anatomy of the Liver Coronary ligament Right lobe Left lobe Falciform ligament Round ligament Gallbladder c Anatomical landmarks on the anterior surface of the liver © 2015 Pearson Education, Inc. Figure 25.19d Anatomy of the Liver Coronary ligament Left hepatic vein Inferior vena cava Caudate lobe Porta Hepatis Left lobe Hepatic portal vein Hepatic artery proper Common bile duct Right lobe Quadrate lobe Gallbladder d The posterior surface of the liver Figure 25.21a Liver Histology Interlobular Bile duct septum Branch of hepatic portal vein Diagrammatic view of lobular organization Portal area Bile ductules Figure 25.21b Liver Histology Central vein Kupffer cells Sinusoid Bile canaliculi Branch of hepatic portal vein Bile duct Branch of hepatic Hepatocytes artery proper Magnified view showing the portal area and central vein Figure 25.21c Liver Histology Branch of hepatic portal vein Branch of hepatic artery Lobules Central vein Interlobular septum Portal area Liver lobules LM 47 Light micrograph showing representative mammalian liver lobules. Human liver lobules lack a distinct connective tissue boundary, making them difficult to distinguish in histological section. Table 25.1 Major Functions of the Liver © 2015 Pearson Education, Inc. Figure 25.22a The Gallbladder and Associated Bile Ducts Round ligament Left hepatic duct Left hepatic artery Common hepatic duct Cut edge of lesser omentum Hepatic portal vein Right hepatic duct Cystic duct Fundus Gallbladder Body Neck Common bile duct Common hepatic artery Right gastric artery Liver Duodenum A view of the inferior surface of the liver showing the position of the gallbladder and ducts that transport bile from the liver to the gallbladder and duodenum Stomach Pancreas Figure 25.22c The Gallbladder and Associated Bile Ducts Common bile duct Hepatopancreatic sphincter Duodenal ampulla Pancreatic duct Duodenal papilla Intestinal lumen Pancreas A portion of the lesser omentum has been cut away to make it easier to see the relationships among the common bile duct, the hepatic duct, and the cystic duct. Figure 25.23a The Pancreas Tail of Caudal Splenic artery Great pancreatic artery pancreas pancreatic artery Abdominal aorta Celiac trunk Stomach Common hepatic artery Gastroduodenal artery Common bile duct Superior pancreatic artery Superior pancreaticoduodenal artery Lobules Accessory pancreatic duct (to lesser duodenal papilla) Duodenum Transverse Body of pancreas pancreatic artery Head of pancreas Pancreatic duct (to greater duodenal papilla) with common bile duct Superior mesenteric artery Anterior branch Posterior branch Inferior pancreaticoduodenal artery Gross anatomy of the pancreas. The head of the pancreas is tucked into a curve of the duodenum that begins at the pylorus of the stomach. Figure 25.23b The Pancreas Pancreatic Acinar cells Pancreatic islet duct (endocrine) (exocrine) Pancreatic acini Diagrammatic view of the histological organization of the pancreas showing exocrine and endocrine regions Figure 25.22c The Pancreas Duct Pancreatic acini (exocrine) Pancreatic islet (endocrine) Pancreas LM x 120 c Histology of the pancreas showing exocrine and endocrine cells. © 2015 Pearson Education, Inc.
