Layers of Alimentary Canal Organs Four layers Mucosa Submucosa Muscularis externa Serosa

Structural Plan of the Digestive Tube Wall Layer Subdivision of the layer Major Functions Mucosa Surface epithelium Lamina propria: (connective tissue) Smooth muscle layer Secretion of enzymes, mucus, hormones, etc. Absorption of digested foodstuffs Protection against bacterial invasion Submucosa Connective tissue Lymph nodules Nerve Fibers Protection Muscularis externa Circular muscular layer Longitudinal muscle layer Regulates GI Motility Serosa Visceral peritoneum Reduces friction as the GI tract organs work

Organs of the Alimentary Canal continuous coiled hollow tube From mouth to anus Figure 14.1

Stomach Muscularis externa has a third oblique layer in the stomach in addition to the longitudinal layer and the circular layer. The stomach is able to churn, mix, and pummel the food, physically breaking it down into smaller pieces.

Digestive System Terms Appendix: a narrow, blind tube protruding from the cecum, having no known useful function, in humans being 3 to 4 inches (8 to 10 cm) long and situated in the lower right-hand part of the abdomen. Anus: the distal end of the alimentary canal. Esophagus: the part of the alimentary canal between the pharynx and the stomach; no digestive or absorptive role Frendulum: membrane securing the tongue to the floor of the mouth Greater omentum: a two-layered serous membrane attached to the greater curvature of the stomach Hard palate :the anterior portion of the palate, separating the oral and nasal cavities, consisting of the bony framework and covering membranes. Haustra: the small pouches caused by sacculation, which give the colon its segmented appearance Ileocecal valve: physiological sphincter muscle situated at the junction of the small intestine (ileum) and the large intestine, with recent evidence indicating an anatomical sphincter may also be present in humans) Its critical function is to limit the reflux of colonic contents into the ileum Large intestine: organ distal to the small intestine Lesser omentum: a peritoneal fold joining the lesser curvature of the stomach and the first part of the duodenum to the porta hepatis. Mesentry: refers to the peritoneum responsible for connecting the jejunum and ileum (parts of the small intestine) to the back wall of the abdomen. Microvilli: surface projections of a mucosal epithelial cell; increases absorption Oral Cavity= another name for “mouth”; the first portion of the alimentary canal that receives food and saliva; Mastication (chewing) of food; Mixing masticated food with saliva; Initiation of swallowing by the tongue; break down food mechanically Parietal peritoneum: the portion of the largest serous membrane in the body that lines the abdominal wall Peyer’s patches: one of a group of solitary nodules or groups of lymph nodes forming a single layer in the mucous membrane of the small intestine Pharynx: is the part of the throat situated immediately posterior to (behind) the mouth and nasal cavity, and superior to the esophagus and larynx. Common passage for food and air Plicae circulares: the numerous permanent crescentic deep folds of mucous membrane found in the small intestine especially in the lower part of the duodenum and the jejunum; increases absorption Pyloric sphincter (valve): The pyloric sphincter, or valve, is a strong ring of smooth muscle at the end of the pyloric canal which lets food pass from the stomach to the duodenum. Rugae: large folds in the mucous membrane of the stomach. Small Intestine: part of the gastrointestinal tract following the stomach; bile produced by the liver and stored in the gallbladder, is secreted in the small intestine to assist in the absorption of fats; digestion is completed and nutrients and water are absorbed by the blood; pancreatic juice is secreted via the pancreatic duct into duodenum. Soft palate: the fleshy part of the palate, extending from the posterior edge of the hard palate; the uvula projects from its free inferior border Stomach: Mechanically, the stomach churns and grinds the food into smaller and smaller pieces, turning it into a substance of nutrients and gastric juices known as chyme. Tongue: rolls the food into balls or boli (singular: 'bolus') and pushes them to the back of the mouth cavity for swallowing Vestibule: the portion of the oral cavity bounded on one side by the teeth and on the other side by the lips and cheeks. Villi: one of the minute fingerlike processes which more or less thickly cover and give a velvety appearance to the surface of the mucous membrane of the small intestine and serve in the absorption of nutriment and of which each has a central blindly ending lacteal surrounded by blood capillaries and covered with epithelium; increases absorption Visceral peritoneum: That portion of the peritoneum covering the organs of the abdominal cavity

Digestive Structures

Teeth Function is to masticate (chew) food Humans have two sets of teeth Deciduous (baby or “milk”) teeth 20 teeth are fully formed by age two

Teeth Permanent teeth Replace deciduous teeth between the ages of 6 and 12 A full set is 32 teeth, but some people do not have wisdom teeth (third molars) If they do emerge, the wisdom teeth appear between ages of 17 and 25

Classification of Teeth Incisors—cutting Canines—tearing or piercing Premolars—grinding Molars—grinding

Human Deciduous and Permanent Teeth Figure 14.9

Regions of a Tooth Crown—exposed part Enamel—hardest substance in the body Dentin—found deep to the enamel and forms the bulk of the tooth Pulp cavity—contains connective tissue, blood vessels, and nerve fibers Root canal—where the pulp cavity extends into the root

Regions of a Tooth Neck Region in contact with the gum Connects crown to root Root Cementum—covers outer surface and attaches the tooth to the periodontal membrane

Regions of a Tooth Figure 14.10

The Digestive System Functions Ingestion—taking in food Digestion—breaking food down both physically and chemically Absorption—movement of nutrients into the bloodstream Defecation—rids the body of indigestible waste

Organs of the Digestive System Two main groups Alimentary canal (gastrointestinal or GI tract)—continuous coiled hollow tube Accessory digestive organs

Organs of the Alimentary Canal Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anus

Mouth (Oral Cavity) Anatomy Lips (labia)—protect the anterior opening Cheeks—form the lateral walls Hard palate—forms the anterior roof Soft palate—forms the posterior roof Uvula—fleshy projection of the soft palate

Mouth (Oral Cavity) Anatomy Vestibule—space between lips externally and teeth and gums internally Oral cavity proper—area contained by the teeth Tongue—attached at hyoid bone and styloid processes of the skull, and by the lingual frenulum to the floor of the mouth Tonsils Palatine Lingual

Mouth (Oral Cavity) Anatomy Figure 14.2a

Mouth (Oral Cavity) Anatomy Figure 14.2b

Mouth Physiology Mastication (chewing) of food Mixing masticated food with saliva Initiation of swallowing by the tongue Allows for the sense of taste

Pharynx Anatomy Nasopharynx—not part of the digestive system Oropharynx—posterior to oral cavity Laryngopharynx—below the oropharynx and connected to the esophagus

Pharynx Anatomy Figure 14.2a

Pharynx Physiology Serves as a passageway for air and food Food is propelled to the esophagus by two muscle layers Longitudinal inner layer Circular outer layer Food movement is by alternating contractions of the muscle layers (peristalsis)

Esophagus Anatomy and Physiology About 10 inches long Runs from pharynx to stomach through the diaphragm Physiology Conducts food by peristalsis (slow rhythmic squeezing) Passageway for food only (respiratory system branches off after the pharynx)

Layers of Alimentary Canal Organs Mucosa Innermost, moist membrane consisting of Surface epithelium Small amount of connective tissue (lamina propria) Small smooth muscle layer

Layers of Alimentary Canal Organs Figure 14.3

Layers of Alimentary Canal Organs Submucosa Just beneath the mucosa Soft connective tissue with blood vessels, nerve endings, and lymphatics

Layers of Alimentary Canal Organs Figure 14.3

Layers of Alimentary Canal Organs Muscularis externa—smooth muscle Inner circular layer Outer longitudinal layer Serosa—outermost layer of the wall contains fluid-producing cells Visceral peritoneum—outermost layer that is continuous with the innermost layer Parietal peritoneum—innermost layer that lines the abdominopelvic cavity

Layers of Alimentary Canal Organs Figure 14.3

Alimentary Canal Nerve Plexuses Two important nerve plexuses serve the alimentary canal Both are part of the autonomic nervous system Submucosal nerve plexus Myenteric nerve plexus Function is to regulate mobility and secretory activity of the GI tract organs