Digestive System I: Organs and Structure General functions Organs of the Alimentary Canal • Mouth and Teeth • Swallowing • Pharynx, Esophagus o Propulsion • Stomach • Linings and Mesentaries • Small Intestine • Large Intestine The Digestive System and Body Metabolism Digestion • Six essential activities 1. Ingestion 2. Propulsion 3. Mechanical digestion 4. Chemical digestion Ingestion Mechanical digestion • Chewing (mouth) • Churning (stomach) • Segmentation (small intestine) Chemical digestion 5. Absorption 6. Defecation Food Pharynx Esophagus Propulsion • Swallowing (oropharynx) • Peristalsis Stomach (esophagus, stomach, small intestine, large intestine) Absorption Lymph vessel Small intestine Large intestine Defecation Blood vessel Mainly H2O Feces Anus Organs of the Digestive System Organs of the Alimentary Canal Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anus Accessory Digestive Organs Salivary glands Teeth Pancreas Liver Gall bladder Digestive System I: Organs and Structure General functions Organs of the Alimentary Canal • Mouth and Teeth • Swallowing • Pharynx, Esophagus o Propulsion • Stomach • Linings and Mesentaries • Small Intestine • Large Intestine Mouth (Oral Cavity) Anatomy Processes of the Mouth Mechanical Processes • Mastication (chewing) of food using temporal and masseter muscles and teeth • Wetting masticated food with saliva • Initiation of swallowing by the tongue Chemical Processes • Allowing for the sense of taste • Digestion of some starch by salivary amylase in saliva Teeth The role is to masticate (chew) food Humans have two sets of teeth • Deciduous (baby or milk) teeth • 20 teeth are fully formed by age two Permanent teeth • Replace deciduous teeth beginning between the ages of 6 to 12 • A full set is 32 teeth, but some people do not have wisdom teeth Classification of Teeth • Incisors (clipping, nibbling) • Canines (siezing) • Premolars (grinding) • Molars (grinding) Regions of a Tooth Crown – exposed part • Outer enamel • Dentin • Pulp cavity Neck • Region in contact with the gum • Connects crown to root Root • Periodontal membrane attached to the bone • Root canal carrying blood vessels and nerves Pharynx Anatomy and Function Digestive System I: Organs and Structure General functions Organs of the Alimentary Canal • Mouth and Teeth • Swallowing • Pharynx, Esophagus o Propulsion • Stomach • Linings and Mesentaries • Small Intestine • Large Intestine Deglutition Bolus of food Tongue Pharynx Epiglottis Glottis Trachea 1 Upper esophageal sphincter is contracted. During the buccal phase, the tongue presses against the hard palate, forcing the food bolus into the oropharynx where the involuntary phase begins. Figure 23.13, step 1 Deglutition Uvula Bolus Epiglottis Esophagus 2 The uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. Figure 23.13, step 2 Deglutition Bolus 3 The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after entry. Figure 23.13, step 3 Digestive System I: Organs and Structure General functions Organs of the Alimentary Canal • Mouth and Teeth • Swallowing • Pharynx, Esophagus o Propulsion • Stomach • Linings and Mesentaries • Small Intestine • Large Intestine Esophagus Runs from pharynx to stomach through the diaphragm Conducts food by peristalsis (slow rhythmic squeezing) Passageway for food only (respiratory system branches off after the pharynx) Esophageal mucosa contains stratified squamous epithelium • Changes to simple columnar at the stomach Esophageal glands in submucosa secrete mucus to aid in bolus movement Propulsion Peristalsis – alternating waves of contraction Segmentation – moving materials back and forth to aid in mixing Peristalsis Movie Online Peristalsis X-ray movie Digestive System I: Organs and Structure General functions Organs of the Alimentary Canal • Mouth and Teeth • Swallowing • Pharynx, Esophagus o Propulsion • Stomach • Linings and Mesentaries • Small Intestine • Large Intestine Stomach Anatomy and Function cardiac region serosa cardiac sphincter fundus region body region pylorus region rugae of mucosa Muscularis externa Functions of the Stomach Acts as a storage tank for food Site of initial food breakdown Chemical breakdown of protein begins Delivers chyme (processed food) to the small intestine Propulsion in the Stomach Food must first be well mixed Rippling peristalsis occurs in the lower stomach The pylorus meters out chyme into the small intestine (30 ml at a time) The stomach empties in four to six hours Stomach peristalsis interactive animation online Figure 14.15 Specialized Mucosa of the Stomach Simple columnar epithelium • Mucous neck cells – produce a sticky alkaline mucus • Gastric glands – secrete gastric juice • Chief cells – produce protein-digesting enzymes (pepsinogens) • Parietal cells – produce hydrochloric acid • Endocrine cells – produce gastrin Chief Cells Utilize Blood CO2 and Interstitial Cl to Produce HCl Blood capillary Chief cell CO2 CO2 + H2O Carbonic H2CO3 anhydrase H+ K+ Stomach lumen H+-K+ ATPase H+ K+ HCO3– Alkaline tide HCI Parietal cell HCO3– Cl– Cl– HCO3–- Cl– antiporter Cll– Interstitial fluid Figure 23.18 Serous Membranes- Thin linings of organs and body wall Mesenteries are double layers of peritoneum •Routes for blood vessels, lymphatics, and nerves; holds organs in place and stores fat • Parietal serosae line internal body walls • Visceral serosae cover internal organs Retroperitoneal organs lie posterior to the peritoneum (e.g. the liver); intraperitoneal (peritoneal) organs are surrounded by the peritoneum Mesenteries of the Stomach Layers of peritoneum (serosa) attached to the stomach = mesentaries Lesser omentum – attaches the liver to the lesser curvature Greater omentum – attaches the greater curvature to the posterior body wall Contains fat to insulate, cushion, and protect abdominal organs Lesser omentum Greater omentum Digestive System I: Organs and Structure General functions Organs of the Alimentary Canal • Mouth and Teeth • Swallowing • Pharynx, Esophagus o Propulsion • Stomach • Linings and Mesentaries • Small Intestine • Large Intestine Small Intestine The body’s major digestive organ Site of nutrient absorption into the blood Muscular tube extending form the pyloric sphincter to the ileocecal valve Suspended from the posterior abdominal wall by the mesentery (omenta) Regions of the Small Intestine • Duodenum o Attached to the stomach o Curves around the head of the pancreas • Jejunum o Attaches anteriorly to the duodenum • Ileum o Extends from jejunum to large intestine Four Tunics of the Alimentary Canal 1. 2. 3. 4. Absorption in the Small Intestine Absorptive Structures • Absorptive cells • Blood capillaries • Lacteals (specialized lymphatic capillaries) •Intestinal crypt epithelium •Secretory cells that produce intestinal juice • Cells that make antimicrobial chemicals •Stem cells Folds in the Small Intestine • Called circular folds or plicae circulares • Deep folds of the mucosa and submucosa • Do not disappear when filled with food Peyer’s patches in submucosa (collections of lymphatic tissue) Digestive System I: Organs and Structure General functions Organs of the Alimentary Canal • Mouth and Teeth • Swallowing • Pharynx, Esophagus o Propulsion • Stomach • Linings and Mesentaries • Small Intestine • Large Intestine Functions of the Large Intestine Structures Cecum – saclike first part of the large intestine Appendix • Accumulation of lymphatic tissue that sometimes becomes inflamed (appendicitis) • Hangs from the cecum Colon • Ascending • Transverse • Descending • S-shaped sigmoidal Rectum Anus – external body opening Functions Absorption of water Elimination of indigestible food from the body as feces Does not participate in digestion of food Goblet cells produce mucus to act as a lubricant Left colic (splenic) flexure Transverse mesocolon Epiploic appendages Right colic (hepatic) flexure Transverse colon Superior mesenteric artery Haustrum Descending colon Ascending colon IIeum Cut edge of mesentery Teniae coli IIeocecal valve Cecum Vermiform appendix Sigmoid colon Rectum Anal canal (a) External anal sphincter Figure 23.29a Modifications to the Muscularis Externa in the Large Intestine Longitudinal smooth muscle is reduced to three bands (teniae coli); circular muscles still present Muscle bands have some degree of tone Walls are formed into pocketlike sacs called haustra Digestive System I: Organs and Structure General functions Organs of the Alimentary Canal • Mouth and Teeth • Swallowing • Pharynx, Esophagus o Propulsion • Stomach • Linings and Mesentaries • Small Intestine • Large Intestine