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The Digestive System

Explore the detailed anatomy of the digestive system, including the alimentary canal and accessory organs. Learn about ingestion, propulsion, digestion, and absorption processes. Discover the role of peritoneum and blood supply, and delve into the functional anatomy of the mouth, pharynx, esophagus, and stomach.

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The Digestive System

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    1. The Digestive System I. Introduction A. Organs 1. Alimentary Canal or Gastrointestinal Tract 2 .Mouth, pharynx, esophagus, stomach, small & large intestine 3. Accessory digestive organs: teeth, tongue, gallbladder, salivary glands, liver & pancreas; produce saliva, bile & digestive enzymes

    2. The esophagus is a part of the ______, while the pancreas is considered a(n) _______ when it comes to the digestive system. alimentary canal; accessory digestive organ stomach; propulsion organ accessory organs; alimentary canal component pharynx; mechanical digestive organ Answer: a. alimentary canal; accessory digestive organAnswer: a. alimentary canal; accessory digestive organ

    3. B. Digestive Processes 1. Ingestion: 2. Propulsion: swallowing & peristalsis 3. Mechanical digestion: chewing, mixing, segmentation 4. Chemical digestion: catabolic reactions 5. Absorption: into blood or lymph Defecation: http://www.youtube.com/watch?v=sCn5uvvc3WE

    4. C. Digestive Organs Relation to Peritoneum a. Visceral peritoneum: covers surface of most organs b. Parietal peritoneum: lines walls of cavity c. Peritoneal cavity: between layers; serous fluid for lubrication of organs d. Mesentery: connects peritoneum; fused double layer of the parietal; vessels, lymphatics & nerves e. Retroperitoneal organs: pancreas & parts of large intestine; behind peritoneum

    5. 2. Blood Supply a. Splanchic circulation: branches off abdominal aorta b. Hepatic, splenic, left gastric branches of celiac trunk; serve liver, spleen, stomach c. Mesenteric arteries serve small & large intestines d. Receives 1/4 of cardiac output e. Hepatic portal circulation receives nutrient-rich venous blood for metabolic processing or storage

    6. Choose the answer that lists the four layers of the wall of the alimentary canal in the appropriate order from innermost to outermost. Mucosa, submucosa, muscularis externa, and serosa Submucosa, mucosa, serosa, muscularis externa Serosa, mucosa, muscularis externa, submucosa Muscularis externa, submucosa, serosa, mucosa Answer: a. Mucosa, submucosa, muscularis externa, and serosaAnswer: a. Mucosa, submucosa, muscularis externa, and serosa

    8. II. Functional Anatomy A. Mouth, Pharynx & Esophagus 1. Mouth (oral or buccal cavity): lips, cheeks, hard & soft palate, uvula

    10. 2. Tongue: intrinsic & extrinsic skeletal muscles a. Intrinsic: not attached to bone; shape changes for speech & swallowing b. Extrinsic: attach tongue to bones; alter tongue position c. Fungiform: taste bud location; filiform- friction for food manipulation; circumvallate papillae

    11. What are the functions of saliva?

    12. 3. Salivary Glands a. Functions of Saliva 1) Clean mouth 2) Dissolve for taste 3) Moisten & compact food 4) Enzymes for starch digestion b. Extrinsic Salivary Glands (outside oral cavity) 1) Parotid: near ears; serous cells only 2) Submandibular: serous & mucous cells 3) Sublingual: mostly mucous cells

    14. c. Intrinsic salivary or buccal glands: throughout oral cavity mucosa; serous & mucous cells Composition of saliva: 97-99.5% water; pH 6.75-7; electrolytes, amylase, mucin, lysozyme, IgA, and metabolic wastes Control of salivation: parasympathetic; strongest reaction of chemoreceptors is to acidic substances, pressoreceptors activated by mechanical stimulus http://www.youtube.com/watch?v=YiXW8jn71gE

    15. 4. Teeth a. Dentition & Dental Formula 1) Primary dentition: deciduous (milk or baby teeth) 2) Permanent dentition: incisors (2 pair), canines (1pair), premolars (2 pair), molars (3 pair) = 32 teeth

    17. b. Tooth Structure 1) Crown: above gum 2) Enamel: mineralized with calcium salts; hardest body substance 3) Root: connected to crown by neck 4) Cementum: attaches root to periodontal ligament 5) Dentin: bonelike under enamel; surrounds pulp cavity 6) Root canal

    18. 5. Pharynx: oro- and laryngopharynx 6. Esophagus a. a muscular tube that moves food b. epiglottis closes off the larynx to food entry 7. Digestive Processes in the mouth and esophagus: a. Mastication or chewing b. Deglutition or swallowing

    21. What is chyme?

    22. B. Stomach http://www.youtube.com/watch?v=Uzl6M1YlU3w 1. Gross Anatomy a. Chyme: paste formed when food mixes with digestive juices b. Rugae: folds when empty c. Regions: cardiac, fundus, body, pyloric d. Pyloric sphincter: controls emptying e. Greater & lesser omentum: tether stomach to other organs & body wall

    23. 2. Microscopic Anatomy a. Mucosa 1) Surface epithelium: simple columnar, mostly goblet cells for protective mucus secretion b. Submucosa c. Three layers of smooth muscle: 1. oblique, 2. circular, 3. longitudinal 4. serosa

    24. Name the gastric glands in the stomach; what does each secrete?

    25. e. Gastric Glands 1) Gastric pits lead into these glands 2) Secrete gastric juice 3) Mucous neck cells: special mucus type 4) Parietal cells: produce HCl 5) Chief or zymogenic cells: produce pepsinogen, the inactive form of pepsin 6) Enteroendocrine cells: release gastrin, histamine, endorphins, serotonin, CCK, somatostatin.

    26. f. Mucosal barrier 1) Alkaline mucus layer 2) Tight junctions of epithelial cells prevent gastric juice from entering underlying tissues

    28. What regulates gastric secretion?

    29. 3. Digestive Processes a. General 1) Storage 2) Mixing of food 3) Protein digestion begins here 4) Alcohol & aspirin pass through walls b. Regulation of Gastric Secretion - both neural and hormonal mechanisms: 1) Cephalic (reflex) phase: seeing, smelling food = vagal impulses (PNS)to enteric nervous system. 2) Gastric phase: distension excites stretch receptors. Chemoreceptors. 3) Intestinal phase: inhibitory signals (nervous and endocrine) to stomach = slow down phase for efficiency and remains there until next cephalic phase

    30. c. Gastric motility & emptying Stomach contractions churn and mix food into chyme. The mechanical action breaks up solids. 2) Regulation of emptying: empties within 4 hours; depends on contents of duodenum.

    31. What ducts enter the duodenum?

    32. C. Small Intestine 1. Gross Anatomy a. Pyloric sphincter to illeocecal valve to large intestine b. Segments 1) Duodenum (du" o-de' num): 10 inches 2) Jejunum: 8 feet 3) Ileum: 12 feet

    34. 2. Microscopic Anatomy a. Modifications for Absorption 1) Plicae circulares: permanent folds of mucosa & submucosa that spiral chyme 2) Villi: contain a lacteal 3) Microvilli: form brush border; brush border enzymes

    36. c. Intestinal Juice 1) 1-2 L per day that is a carrier fluid for absorption of nutrients from chyme. 2) Water, mucus, (most enzymes are brush border or bound enzymes) 3.) Located deep in the crypts and also contain lysozyme, and antibacterial enzyme

    37. D. Liver & Gallbladder Liver Function - produces bile for export to the duodenum. Also the fuel filter of the body. Bile a. Bile salts: emulsify fats b. Bilirubin: bile pigment: waste product of heme portion of Hgb

    38. 4. Gallbladder: stores bile 5. Regulation of Bile Release CCK is major stimulus for gallbladder contraction Stimulated by acidic, fatty chyme in duodenum http://www.youtube.com/watch?v=VJorMTL58qI d. Gallstones: not enough bile salts in bile to solubilize cholesterol, therefore cholesterol crystallizes

    39. What enzymes are produced by the pancreas?

    40. E. Pancreas - enzyme factory that produces enzymes that break down all food categories and then delivers to duodenum 1. Pancreatic Juice a. Acini: full of zymogen granules containing enzymes b. Pancreatic proteases: trypsin (activated by enterokinase), carboxypeptidase & chymotrypsin (activated by trypsin) c. Amylase, lipases & nucleases also (secreted in active form) 2. Regulation of Secretion: a. Secretin released due to HCl in intestine; targets duct cells to release bicarbonate b. CCK released in response to proteins & fats; stimulates enzyme release

    41. In terms of digestion, the large intestine’s greatest contribution is: exposing the chyme to the rich assortment of pancreatic enzymes through the process of segmentation. absorption of all primary nutrients. absorption of water. regulation of gastric motility. Answer: c. absorption of water.Answer: c. absorption of water.

    42. F. Large Intestine 1. Gross Anatomy a. Teniae coli: three bands of longitudinal muscle b. Divisions: cecum, appendix, colon, rectum & anal canal, vermiform appendix c. Colon: ascending, transverse, descending & sigmoid d. Internal & external anal sphincters 2. Microscopic Anatomy a. No villi or digestive enzymes b. Thicker mucosa and crypts deeper with many goblet cells

    44. 3. Bacterial flora a. Ferment some of indigestible carbohydrates, releasing acids and gases b. Synthesize B complex vitamins & most of vitamin K for clotting proteins 4. Digestive Processes a. Water recovery b. Propulsion is major function c. Movements 1) Haustral contractions: slow, segmenting movements every 30 minutes 2) Mass movements or mass peristalsis: usually after eating (gastrocolic reflex); dietary fiber increases strength of contractions Defecation: spinal parasympathetic reflex; internal anal sphincters relax http://www.youtube.com/watch?v=0nuSzk8WzdM&NR=1 http://www.youtube.com/watch?v=nGyzZyxMxkk&feature=related

    46. III. Physiology of Chemical Digestion & Absorption A. Chemical Digestion 1. Enzyme hydrolysis a. Addition of a water molecule to each molecular bond to be lysed b. Breaks things down into their monomers or building blocks 2. Carbohydrates a. Monosaccharides: simple sugars that can be absorbed; glucose, fructose & galactose b. Salivary amylase begins digestion in mouth & continues in stomach c. Pancreatic amylase d. Intestinal brush border enzymes (dextrinase & glucoamylase, maltase, sucrase & lactase)

    49. 3. Proteins a. Dietary & enzyme proteins converted to amino acid monomers b. Stomach pepsinogen activated to pepsin (a group of enzymes); works best at pH 1.5 -3.5 c. Trypsin, chymotrypsin from pancreas, cleave proteins into smaller peptides d. Pancreatic carboxypeptidase splits off one A.A. e. Brush border enzymes aminopeptidase & dipeptidase

    51. 4. Lipids a. Lipases from pancreas only b. Bile salts emulsify fats; reduction of attraction between fat molecules so they can be dispersed c. End product: free fatty acids and glycerides 5. Nucleic acids: pancreatic nucleases hydrolyze to nucleotides

    52. B. Absorption 1. General a. Up to 10 L consumed daily but 0.5-1 L reaches large intestine b. Most occurs in small intestine by the time it reaches ileum c. Ileum reclaims bile salts d. Active transport is primary mechanism 2. Carbohydrates: protein carriers into epithelial cells 3. Proteins: many different carriers; coupled to active transport of sodium 4. Lipids a. Micelles - collections of fatty elements clustered with bile salts - move through membranes by simple diffusion Chylomicrons formed inside epithelial cells Chylomicrons cannot pass through basement membrane of capillaries and enter lacteals instead; hydrolyzed in blood to free fatty acids by lipoprotein lipase

    53. Nucleic acids: carriers Vitamins a. A, D, E & K dissolve in dietary fats b. Water-soluble vitamins absorbed by diffusion Vitamin B12 is large and binds to intrinsic factor from stomach & is endocytosed in ileum Electrolytes: iron & calcium in duodenum; others throughout small intestine Water: 95% absorbed by osmosis

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