23 The Digestive System

I. Overview of the Digestive System A. Organs are divided into two groups 1. Alimentary canal ► mouth, pharynx, and esophagus ► stomach, small intestine, and large intestine, rectum 2. Accessory digestive organs ► teeth and tongue ► gallbladder, salivary glands, liver, and pancreas i. connected to the alimentary canal by ducts ii. secretions contribute to breakdown of foodstuffs

3 Mouth (oral cavity) Parotid gland Sublingual gland Tongue Salivary glands Submandibular gland Pharynx Esophagus Stomach Pancreas (Spleen) Liver Gallbladder Transverse colon Descending colon Duodenum Small intestine Jejunum Ascending colon Ileum Large intestine Cecum Sigmoid colon Rectum Appendix Anus Anal canal 3

II. Abdominal Regions A. Four lines divide abdominal wall into nine regions 1. Midclavicular lines - vertical lines of grid 2. Subcostal plane - superior horizontal line 3. Transtubercular plane - inferior horizontal line B. Four quadrants – cross with point in the umbilicus 1. Right upper quadrant 2. Left upper quadrant 3. Right lower quadrant 4. Left lower quadrant

Right hypochondriac region Left hypochondriac region Epigastric region Right lumbar region Left lumbar region Umbilical region Right iliac (inguinal) region Hypogastric (pubic) region Left iliac (inguinal) region Nine regions delineated by four planes 5

Transverse colon of large intestine Ascending colon of large intestine Liver Diaphragm Gallbladder Stomach Transverse colon of large intestine Ascending colon of large intestine Small intestine Descending colon of large intestine Cecum Initial part of sigmoid colon Appendix Urinary bladder Anterior view of the nine regions showing the superficial organs 6

III. The Peritoneal Cavity and Peritoneum A. Imagine the digestive organs surrounded by plastic wrap 1. some of it touches the surface of the organ (“visceral”) 2. some of it touches the outer area of the organ (“parietal”) 3. like a hose that is surrounded by plastic wrapping B. Peritoneum - a serous membrane around the digestive organs 1. visceral peritoneum - surrounds digestive organs on surface 2. parietal peritoneum – part that touches the outside a. peritoneal cavity – space between these two layers

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C. Mesentery - a double layer of peritoneum 1. holds organs in place 2. sites of fat storage 3. provides a route for circulatory vessels and nerves 4. it is the “sheet” that envelopes the intestines D. Ventral mesenteries 1. Falciform ligament - binds anterior part of liver to anterior abdominal wall; between lobes of the liver 2. Lesser omentum - attaches liver to lesser curvature of stomach

E. Dorsal mesenteries 1. Greater omentum - connects greater curvature of stomach to posterior abdominal wall a. a “fatty apron” flapped over the digestive organs 2. Transverse mesocolon - holds transverse colon in place 3. Sigmoid mesocolon - connects the sigmoid colon to posterior pelvic wall F. Retroperitoneal organs - behind the peritoneum G. Peritoneal organs - digestive organs that keep their mesentery

Liver Gallbladder Lesser omentum Stomach Duodenum Transverse colon Small intestine Cecum Urinary bladder 12

Greater omentum Transverse colon Transverse mesocolon Descending colon Mesentery Sigmoid mesocolon Jejunum Sigmoid colon Ileum 13

Gastrosplenic ligament Ligamentum teres Gallbladder Lesser omentum Spleen Liver Gastrosplenic ligament Transverse mesocolon Pancreas Stomach, pyloric part Duodenum, superior part Transverse colon Duodenum, horizontal part Duodenojejunal flexure Greater omentum Descending colon Ascending colon Mesentery (cut) Sigmoid mesocolon Rectum Ileum Cecum 14

Falciform ligament Liver Gallbladder Spleen Stomach Ligamentum teres Greater omentum Small intestine Cecum 15

IV. Histology of the Alimentary Canal Wall A. Same four layers from esophagus to anus 1. mucosa—innermost layer a. epithelium b. lamina propria c. muscularis mucosae 2. submucosa—external to the mucosa a. contains blood and lymphatic vessels, nerve fibers

3. muscularis externa - external to the submucosa a. circular muscularis - inner layer b. longitudinal muscularis - outer layer 4. serosa—the outermost layer – is the visceral peritoneum

Mucosa Epithelium Lamina propria Muscularis mucosae Submucosa Muscularis externa Circular layer Longitudinal layer Serosa Epithelium Connective tissue Nerve Lumen Artery Vein Mesentery Lymphatic vessel Longitudinal and cross-sectional views through the small intestine 18

Mucosa Submucosa Muscularis externa Serosa Light micrograph cross section through the small intestine (85) 19

Longitudinal layer of smooth muscle (shows smooth muscle fibers in cross section, 215) Small intestine Mucosa Location and plane of section shown in (b) Cross section of the intestine showing the smooth muscle layers (one circular and the other longitudinal) running at right angles to each other Circular layer of smooth muscle (shows longitudinal views of smooth muscle fibers, 215) 20

V. Nerve Plexuses A. Myenteric nerve plexus 1. lies between circular and longitudinal muscularis 2. controls peristalsis and segmentation B. Submucosal nerve plexus 1. lies in submucosa 2. signals glands to secrete C. Innervation - sympathetic and parasympathetic motor fibers

VI. The Mouth and Associated Organs A. Borders of the mouth ► Lips anteriorly ► Cheeks laterally ► Palate superiorly ► Tongue inferiorly ► Fauces of oropharynx posteriorly B. lips and cheeks - formed from orbicularis oris and buccinator C. Mucosal layer - stratified squamous epithelium

Sagittal section of the oral cavity and pharynx Soft palate Uvula Hard palate Nasopharynx Palatine tonsil Tongue Oropharynx Lingual tonsil Epiglottis Hyoid bone Laryngopharynx Esophagus Trachea Sagittal section of the oral cavity and pharynx 23

Sagittal section of the oral cavity and pharynx Uvula Nasopharynx Oropharynx Laryngopharynx Sagittal section of the oral cavity and pharynx 24

D. labial frenulum - connects lips to gum E. palate - forms the roof of the mouth (hard and soft) F. Boundaries of the fauces ► palatoglossal arches ► palatopharyngeal arches

Superior labial frenulum Palatoglossal arch Hard palate Soft palate Palatopharyngeal arch Uvula Lingual frenulum Gingivae (gums) Inferior labial frenulum Anterior view 26

VII. The Tongue A. Interlacing fascicles of skeletal muscle B. Grips food and repositions it C. Helps form some consonants D. Intrinsic muscles - within the tongue E. Extrinsic muscles - external to the tongue F. Lingual frenulum - secures tongue to floor of mouth G. Papillae – different “bumps” on the tongue for taste, etc.

Medial sulcus of the tongue Epiglottis Terminal sulcus Foliate papillae Vallate papilla Medial sulcus of the tongue Dorsum of tongue Fungiform papilla Filiform papilla 28

VIII. The Teeth A. Deciduous teeth – (20 teeth) - first appear at 6 months of age B. Permanent teeth – (32 teeth) - by the end of adolescence C. Types of teeth: ► Incisors (8) ► Canines (4) ► Premolars (8) ► Molars (12)

Incisors Central (6–8 mo) Lateral (8–10 mo) Canine (eyetooth) (16–20 mo) Molars First molar (10–15 mo) Deciduous (milk) teeth Second molar (about 2 yr) Incisors Central (7 yr) Lateral (8 yr) Canine (eyetooth) (11 yr) Premolars (bicuspids) First premolar (11 yr) Second premolar (12–13 yr) Molars First molar (6–7 yr) Second molar (12–13 yr) Third molar (wisdom tooth) (17–25 yr) Permanent teeth 30

IX. Tooth Structure A. Crown - exposed surface B. Neck – at gum line B. Root - in tooth socket C. Enamel – outer layer D. Dentin - underlies enamel E. Pulp cavity - center of tooth F. Periodontal ligament – attaches tooth to bone

Pulp cavity (contains blood vessels and nerves) Enamel Dentin Crown Pulp cavity (contains blood vessels and nerves) Neck Gingiva (gum) Cement Root canal Root Periodontal ligament 32

Pulp cavity (contains blood vessels and nerves) Gingiva (gum) Cement 33

X. The Salivary Glands B. Parotid glands – in the cheeks A. Produce saliva B. Parotid glands – in the cheeks C. Submandibular glands - along medial surface of mandible D. Sublingual glands - lie in floor of oral cavity

35 Parotid gland Ducts of sublingual gland Parotid duct Submandibular duct Submandibular gland Mucous cells Serous cells forming demilunes 35

XI. The Esophagus A. A long muscular tube – moves food by peristalsis B. Begins as a continuation of the pharynx C. Joins the stomach inferior to the diaphragm D. Cardiac sphincter—closes lumen to prevent stomach acid from entering esophagus E. Statified squamous epithelium F. Skeletal muscle ---- mixed skeletal/smooth ---- smooth muscle

Mucosa (stratified squamous epithelium) Esophagus- stomach junction Submucosa (areolar connective tissue) Lumen Muscularis externa Simple columnar epithelium of stomach Circular layer Longitudinal layer Adventitia (fibrous connective tissue) Cross section through esophagus (3) Esophagus-stomach junction, longitudinal section (85) 37

XII. The Stomach A. Site where food is churned into chyme B. Regions of the stomach ► cardiac region ► fundus ► body ► pyloric region C. Muscularis has three layers 1. circular and longitudinal and oblique layers D. Epithelium is simple columnar epithelium

Cardiac Region Fundus Body Lumen Lesser curvature Rugae of mucosa Muscularis externa Longitudinal layer Circular layer Body Oblique layer Lesser curvature Lumen Rugae of mucosa Greater curvature Pyloric sphincter Pyloric region 39

E. Mucosa dotted with gastric pits with gastric glands F. Pyloric sphincter – valve that leads to small intestine G. Rugae – folds along the inner surface H. Greater and Lesser curvatures

Cardiac Region Fundus Body Lumen Lesser curvature Rugae of mucosa Muscularis externa Longitudinal layer Circular layer Body Oblique layer Lesser curvature Lumen Rugae of mucosa Greater curvature Pyloric sphincter Pyloric region 41

Fundus Liver (cut) Body Spleen Lesser curvature Greater curvature 42

Mucosa layer of stomach A gastric ulcer lesion Bacteria Mucosa layer of stomach H. pylori bacteria 43

XIII. The Small Intestine A. Longest portion of the alimentary canal B. Site of most enzymatic digestion and absorption C. Three subdivisions ► duodenum (1 foot) ► jejunum (next 8 feet) ► ileum (last 12 feet) D. Innervation 1. parasympathetic fibers from vagus nerve 2. sympathetic from thoracic splanchnic nerves

E. Duodenum 1. receives digestive enzymes and bile 2. Main pancreatic duct and common bile duct enter duodenum 3. Sphincters control entry of bile and pancreatic juices

46 Right and left hepatic ducts of liver Common hepatic duct Cystic duct Bile duct and sphincter Accessory pancreatic duct Pancreas Gallbladder Main pancreatic duct and sphincter Hepatopancreatic ampulla and sphincter Duodenum 46

F. Modifications for absorption 1. circular folds - transverse ridges of mucosa and submucosa 2. Villi - fingerlike projections of the mucosa a. covered with simple columnar epithelium 3. microvilli - further increase surface area for absorption 4. lacteals – special lymphatic vessels of the intestine

Villi Microvilli 48 Lumen Circular folds Absorptive enterocytes Goblet cells Lacteal Villi Vilus Intestinal crypt 48

XIV. The Large Intestine A. Small amount of digestion by bacteria B. Main functions - Absorb water and electrolytes C. Mass peristaltic movements force feces toward the rectum D. Subdivided into: cecum, appendix, colon, rectum, anal canal E. Special features of large intestine 1. teniae coli - thickening of longitudinal muscularis layer 2. haustra - puckering created by teniae coli 3. epiploic appendages - fat-filled pouches of visceral peritoneum

External anal sphincter Epiploic appendages Transverse colon Descending colon Haustrum Ascending colon Teniae coli Sigmoid colon Appendix Rectum Anal canal External anal sphincter 50

External anal sphincter 51

F. Cecum - beginning of large intestine G. Appendix - contains lymphoid tissue; neutralizes pathogens H. Colon - Divided into distinct segments ► ascending colon ► transverse colon ► descending colon ► sigmoid colon I. Rectum - descends along the inferior half of the sacrum J. Anal canal - the last subdivision of the large intestine 1. lined with stratified squamous epithelium

Left colic (splenic) flexure Right colic (hepatic) flexure Epiploic appendages Transverse colon Superior mesenteric artery Descending colon Haustrum Ascending colon Ileocecal valve Teniae coli Sigmoid colon Cecum Appendix Rectum Anal canal External anal sphincter 53

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K. Vessels of the Large Intestine 1. superior mesenteric artery – first half 2. inferior mesenteric artery- second half 3. NOTE: hepatic portal vein to the liver L. Vagus Nerve (X) – supplies parasympathetic innervation M. Microscopic Anatomy 1. villi are absent 2. contains numerous goblet cells that secrete mucus 3. intestinal crypts - simple tubular glands 4. lined with simple columnar epithelial tissue

Goblet cells Intestinal crypt Muscularis mucosae 56

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XV. The Liver A. Largest gland in the body - performs over 500 functions B. Production of bile to digest fats C. Stores and distributes nutrients for the body D. Four lobes: right, left, caudate, quadrate E. Falciform ligament - divides right and left lobes F. Ligamentum teres (round ligament) – at the base

G. Hepatic PORTAL vein – from intestines to the liver H. Hepatic vein – from liver to inferior vena cava G. Common hepatic duct – from liver to gall bladder H. Cystic duct – from gall bladder to common bile duct

Round ligament (ligamentum teres) Gallbladder Sternum Nipple Liver Falciform ligament Right lobe of liver Left lobe of liver Round ligament (ligamentum teres) Gallbladder 61

Caudate lobe of liver Left lobe of liver Quadrate lobe of liver Right lobe of liver Gallbladder Ligamentum teres 62

!!! NOTE !!! Hepatic portal vein Hepatic veins Caudate lobe Left lobe Cystic duct Common hepatic duct Gallbladder Fissure Right lobe Falciform ligament Quadrate lobe Ligamentum teres 63

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I. Microscopic Anatomy of the Liver 1. hepatocyte—functional cells of the liver 2. lobule – hexagonal component of the liver 3. portal triad composed of ► bile duct tributary ► branch of hepatic portal vein ► branch of hepatic artery 4. hepatic macrophages - destroy bacteria

A Lobule 66 Lobule Central vein Connective tissue septum Interlobular veins (to hepatic vein) Central vein Sinusoids Bile canaliculi A Lobule Plates of hepatocytes Bile duct (receives bile from bile canaliculi) Fenestrated lining (endothelial cells) of sinusoids Bile duct Portal venule Portal triad Stellate macrophages in sinusoid walls Portal arteriole Portal vein 66

XVI. The Gallbladder A. Stores and concentrates bile B. Expels bile into duodenum - bile emulsifies fats

XVII. The Pancreas A. Has both exocrine and endocrine functions 1. Endocrine function - produces insulin and glucagon 2. Exocrine function – produces most digestive enzymes a. delivered to duodenum via pancreatic duct B. Head of the pancreas – circled by the duodenum C. Tail of the pancreas – short extension

69 Right and left hepatic ducts of liver Common hepatic duct Cystic duct Bile duct and sphincter Accessory pancreatic duct Tail of pancreas Pancreas Gallbladder Main pancreatic duct and sphincter Hepatopancreatic ampulla and sphincter Duodenum Head of pancreas 69