Meyers' A&P March 25, 2015 Unit 9 The Digestive System I. Functions of the Digestive System • Ingestion: The taking in of food. • Propulsion: Movement caused by force. • Digestion: The breakdown of foodstuffs > Mechanical: > Chemical: • Absorption: • Defecation: Physical breakdown of food stuff. Chemical breakdown of food stuff. Intake of nutrients from food. Elimination of indigestible waste. 1 Meyers' A&P March 25, 2015 II. Organs of the Alimentary Canal (GI Tract) A. Oral Cavity: Mechanical & Chemical Digestion > Tongue – Mixes food with saliva, initiates swallowing, has taste buds > Salivary Glands – Create saliva, mixture of mucus & serous fluids « contains Salivary Amylase (digests starch) « creates a BOLUS, helps dissolve food for taste > Taste – Mastication/Chew food (mechanical digestion) > Epiglottis – cartilage blocks trachea opening not allowing food to enter during swollowing > Hard & Soft Palate – Separates oral & nasal cavities – When swallowing, soft palate rises to close nasal passageway 2 Meyers' A&P March 25, 2015 II. Organs of the Alimentary Canal (GI Tract) B. Pharynx: divided into 3 parts > Nasopharynx: respiratory passageway > Oropharynx: most posterior part of oral cavity > Laryngopharynx: most superior part of esophagus C. Esophagus: muscular tube for transport (peristalsis) II. Organs of the Alimentary Canal (GI Tract) D. Stomach: Mechanical & Chemical Digestion > Regions: Cardia, Fundus, Body & Pylorus Churn > Rugae: Folds in the walls of the stomach > Mucosa: lined with simple columnar epithelium and gastric pits which create gastric juice – Chief cells: produce pepsinogen – Parietal cells: produce HCl » Pepsinogen + HCl = Pepsin (breaks down proteins) – Mucous Neck cells: produce alkaline mucus > Sphincter Muscles: on both ends of the stomach, regulate entry and exit of food stuffs > Stomach does aid in the small amount of absorption of fats and alcohol 3 Meyers' A&P March 25, 2015 II. Organs of the Alimentary Canal (GI Tract) E. Small Intestine: Chemical Digestion & Absorption > Regions: – Duodenum – Jejunum – Ileum > Mesentery: Webbing Filled with blood Vessels > Pancreatic juices and bile enter small intestine (duodenum) – help with complete break down of food particles > Structural modifications: – Microvilli: Cellular projections – Villi: Fold in Epithelial Tissue – Plicae Circulares: Fold in Intestinal Wall 4 Meyers' A&P March 25, 2015 II. Organs of the Alimentary Canal (GI Tract) F. Large Intestine: Water Absorption & Waste Excretion > Regions: – Cecum (Appendix) – Colon » Ascending » Transverse » Descending » Sigmoid – Rectum – Anal Canal 5 Meyers' A&P March 25, 2015 III. Anatomy of the Alimentary Canal (GI Tract) • From the Esophagus to the Large Intestine, the wall of the GI Tract is composed of... – Mucosa: innermost layer of epithelial tissue » Lined with goblet cells producing mucus – Submucosa: connective tissue containing... » Blood vessels, nerves & lymphatic tissue – Muscularis Externa: Layers of smooth muscles » Varies between the organs – Serosa: Outermost layer » Peritoneum & Mesentery IV. Accessory Digestive Organs A. Pancreas: Flat gland, extends from spleen to duodenum > Produces pancreatic juice consisting of enzymes that aid in chemical digestion – Protease: Proteins -> smaller peptides – Pancreatic Amylase: Complex Sugars -> Dissacharides – Lipase: Fats -> Glycerol & Fatty Acids – Nuclease: Cleaves nucleic acids (DNA/RNA) > Secreted in alkaline solution > Emptied into duodenum 6 Meyers' A&P March 25, 2015 IV. Accessory Digestive Organs B. Liver: Large lobed (4) organ, located just inferior to diaphragm > Produces bile – yellow-green fluid containing bile salts, pigments, cholesterol, phospholipids & electrolytes > Emulsification: Bile salts break large fat globules into smaller ones – increases surface area of lipids for lipase > Exits liver via hepatic duct 7 Meyers' A&P March 25, 2015 IV. Accessory Digestive Organs C. Gallbladder: sac-like organ imbedded on underside of liver > bile leaving liver backs up into gallbladder via cystic duct > bile is concentrated in gallbladder – secrete into duodenum via bile duct when fatty food present D. Salivary Glands: Parotid, Sublingual, Submandibular > Produce and secrete saliva into oral cavity – Mucus to moisten food – Salivary Amylase for starch digestion – Lysozyme & Antibodies to fight infection – Dissolves food chemicals for taste V. Chemical Digestion & Absorption Carbohydrates Starch Oral Cavity Salivary Amylase Proteins Proteins Pepsin Stomach large polypeptides Nucleic Acids Fats/lipids DNA/RNA Triglycerides/Fats Lumen of Small Intestine Pancreatic Amylase disaccharides Pancreatic Proteases small polypeptides Epithelium of Small Intestine brush border enzymes brush border enzymes brush border enzymes amino acids nucleotides monosaccharides Pancreatic Nucleases Pancreatic Lipases glycerol & fatty acids *all (except some lipids) absorbed in blood...to liver...to rest of body *some lipid breakdown products absorbed in blood, some in lymph...all end up in liver...then to rest of body 8 Meyers' A&P March 25, 2015 VI. Metabolism • All reactions that help maintain life A. Anabolism: reactions that build molecules B. Catabolism: reactions that breaks down molecules – digestion is a catabolic process – chemical digestion utilizing enzymes (hydrolysis) 1. Carbohydrate metabolism: 2. Fat Metabolism: 3. Protein Metabolism: 9
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