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Digestive System I: Organs and Structure
General functions Organs of the Alimentary Canal Mouth and Teeth Swallowing Pharynx, Esophagus Propulsion Stomach Linings and Mesentaries Small Intestine Large Intestine
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The Digestive System and Body Metabolism
Digestion Six essential activities Ingestion Propulsion Mechanical digestion Chemical digestion Absorption Defecation Ingestion Food Mechanical digestion Pharynx • Chewing (mouth) Esophagus • Churning (stomach) Propulsion • Segmentation (small intestine) • Swallowing (oropharynx) Chemical digestion • Peristalsis (esophagus, stomach, small intestine, large intestine) Stomach Absorption Lymph vessel Small intestine Blood vessel Large intestine Mainly H2O Feces Defecation Anus Figure 23.2
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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
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Digestive System I: Organs and Structure
General functions Organs of the Alimentary Canal Mouth and Teeth Swallowing Pharynx, Esophagus Propulsion Stomach Linings and Mesentaries Small Intestine Large Intestine
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Mouth (Oral Cavity) Anatomy
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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
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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)
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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
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Pharynx Anatomy and Function
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Digestive System I: Organs and Structure
General functions Organs of the Alimentary Canal Mouth and Teeth Swallowing Pharynx, Esophagus Propulsion Stomach Linings and Mesentaries Small Intestine Large Intestine
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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
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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
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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
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Digestive System I: Organs and Structure
General functions Organs of the Alimentary Canal Mouth and Teeth Swallowing Pharynx, Esophagus Propulsion Stomach Linings and Mesentaries Small Intestine Large Intestine
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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
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Propulsion Peristalsis – alternating waves of contraction
Segmentation – moving materials back and forth to aid in mixing Peristalsis Movie Online Peristalsis X-ray movie
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Digestive System I: Organs and Structure
General functions Organs of the Alimentary Canal Mouth and Teeth Swallowing Pharynx, Esophagus Propulsion Stomach Linings and Mesentaries Small Intestine Large Intestine
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Stomach Anatomy and Function
cardiac region serosa cardiac sphincter lesser curvature fundus region greater curvature Muscularis externa body region pylorus region 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 rugae of mucosa
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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
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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
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Chief Cells Utilize Blood CO2 and Interstitial Cl to Produce HCl
capillary Chief cell Stomach lumen CO2 CO2 + H2O H+-K+ ATPase Carbonic anhydrase H2CO3 H+ H+ K+ K+ HCO3– HCI Alkaline tide Parietal cell HCO3– Cl– Cl– Cl– l HCO3–- Cl– antiporter Inter- stitial fluid Figure 23.18
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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 Retroperitoneal organs lie posterior to the peritoneum (e.g. the liver); intraperitoneal (peritoneal) organs are surrounded by the peritoneum Parietal serosae line internal body walls Visceral serosae cover internal organs
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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
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Digestive System I: Organs and Structure
General functions Organs of the Alimentary Canal Mouth and Teeth Swallowing Pharynx, Esophagus Propulsion Stomach Linings and Mesentaries Small Intestine Large Intestine
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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 Attached to the stomach Curves around the head of the pancreas Jejunum Attaches anteriorly to the duodenum Ileum Extends from jejunum to large intestine
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Four Tunics of the Alimentary Canal
1. 2. 3. 4.
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Absorption in the Small Intestine
Absorptive Structures Absorptive cells Blood capillaries Lacteals (specialized lymphatic capillaries) 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) Intestinal crypt epithelium Secretory cells that produce intestinal juice Cells that make antimicrobial chemicals Stem cells
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Digestive System I: Organs and Structure
General functions Organs of the Alimentary Canal Mouth and Teeth Swallowing Pharynx, Esophagus Propulsion Stomach Linings and Mesentaries Small Intestine Large Intestine
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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
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External anal sphincter (a)
Right colic (hepatic) flexure Left colic (splenic) flexure Transverse mesocolon Transverse colon Epiploic appendages Superior mesenteric artery Descending colon Haustrum Ascending colon Cut edge of mesentery IIeum Teniae coli IIeocecal valve Sigmoid colon Cecum Vermiform appendix Rectum Anal canal External anal sphincter (a) Figure 23.29a
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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
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Digestive System I: Organs and Structure
General functions Organs of the Alimentary Canal Mouth and Teeth Swallowing Pharynx, Esophagus Propulsion Stomach Linings and Mesentaries Small Intestine Large Intestine
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