Digestive System Part I: Alimentary Canal
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| Organs of the digestive system | consist of those that form the digestive tract and those that are called accessory organs.
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| Digestive tract/alimentary canal/gastrointestinal (GI) tract | make up a hollow tube that extends from oral cavity to anus; consist of organs – mouth, pharynx, esophagus, stomach, small intestine, large intestine
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| Mouth, pharynx, esophagus, stomach, small intestine, large intestine | organs of the alimentary canal/GI tract
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| Accessory organs of digestive System | empty their products into the alimentary canal via ducts; include these organs – salivary glands, liver, gallbladder, pancreas
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| Salivary glands, liver, gallbladder, pancreas | accessory organs of digestive system
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| Ingestion | eating food, drinking liquids
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| Propulsion | movement of food through alimentary canal; includes swallowing and peristalsis
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| Swallowing | part of propulsion; voluntary process dependent on skeletal muscle
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| Peristalsis | major means of propulsion; involuntary process dependent on smooth muscle; involves alternate waves of contraction & relaxation of musculature in the organ walls; net effect is to squeeze food from one organ to the next
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| Mechanical/Physical Digestion | the physical manipulation of food to prepare it for enzymatic chemical digestion; exemplified by the chewing of food by teeth and the churning of food by the stomach.
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| Chemical Digestion | refers to the chemical breakdown of large, complex food molecules into smaller building block molecules via enzymes; includes enzymatic breakdown of large carbohydrates to simple sugars, proteins to amino acids, lipids to fatty acids
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| Absorption | primarily involves movement of digested end products from lumen of GI tract into blood in blood capillaries; but some lipids/fats are also absorbed into lymph in lymphatic capillaries called lacteals
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| Defecation | elimination of largely indigestible material from the body via anus in form of feces
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| Same from digestive tract through large intestine; Mucosa, submucosa, muscularis externa, serosa (visceral peritoneum) | Histology of the alimentary canal wall; four major/general layers from inner to outermost
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| Mucosa | innermost layer of GI tract; mucous membrane; three specific layers – lining epithelium, lamina propria, muscularis mucosae
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| Simple columnar epithelium | specific epithelium tissue component of lining epithelium of most of digestive tract, including stomach, small intestine, large intestine
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| Stratified squamous epithelium | specific epithelium tissue component of mouth, most of pharynx, esophagus due to greater physical abrasion from food
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| Lining epithelium, lamina propria, muscularis mucosae | three specific sublayers of mucosa
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| Lining epithelium | specific layer of mucosa; lines actual lumen of the GI tract so has direct contact with food; specific epithelial tissue component is simple columnar epithelium
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| Lamina propria | specific layer of mucosa; connective tissue positioned deep to lining epithelium; contains most of mucosa-associated lymphoid tissue (MALT) which defends against invasion by bacteria and other microbes in GI tract
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| Mucosa-associated lymphoid tissue (MALT) | tissue that defends against invasion by bacteria and other microbes in the GI tract
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| Muscularis mucosae | specific layer of mucosa; very thin layer of smooth muscle external to lamina propria
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| Submucosa | layer of GI tract; external to mucosa; consists of connective tissue
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| Musularis externa | layer of GI tract; external to submucosa; usually 2 sublayers-longitudinal and circular layer of smooth muscle; 3rd oblique layer present in stomach; contractions mix food in, and propel food through alimentary canal and provide for peristalsis
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| Longitudinal and circular layers | sublayers of smooth muscle tissue found in muscularis externa of GI tract
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| Oblique layer | third sublayer of smooth muscle tissue found only in stomach
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| Parasympathetic division of ANS via vagus nerve | how activity of smooth muscle in muscularis externa is increased thus enhancing digestive tract motility
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| Sympathetic division of ANS via vagus nerve | how activity of smooth muscle in muscularis externa is decreased thus inhibiting digestive tract motility
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| Serosa/visceral peritoneum | outermost layer of GI tract wall; has serous fluid that allows digestive organs to slide easily along one another and against wall of peritoneal cavity
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| Peritonitis | infection & inflammation of peritoneum; usually results from a burst appendix that leaks feces and bacteria into peritoneal cavity
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| Mesentery, greater omentum, falciform ligament | “special folds” of the peritoneum
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| Mesentery | sheet-like structure that fans inferiorly from the posterior abdominal wall like long, pleated curtains to support the long coils of the jejunum and ileum of small intestine
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| Greater omentum | attached to greater curvature of stomach from which it extends inferiorly to cover most of the front of the intestines like a lacy apron
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| Nerve plexuses in wall of alimentary canal | contain both parasympathetic and sympathetic components; psymp components stimulate digestive functions; symp components inhibit digestive functions
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| Myenteric nerve plexus, submucosal nerve plexus | nerve plexuses in wall of alimentary canal
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| Myenteric nerve plexus | nerve plexus of alimentary canal located in musularis externa where it controls smooth muscle activity esp. associated with peristalsis
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| Submucosal nerve plexus | nerve plexus of alimentary canal located in submucosa
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