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Chapter 24 - Introduction to the Digestive System

Chapter 24 - Introduction to the Digestive System - Chapter...

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Chapter 24 - Introduction to the Digestive System The digestive system acquires nutrients from environment Anabolism  - uses raw materials to synthesize essential compounds Catabolism  - decomposes substances to provide energy cells need to function Catabolic Reactions require two essential ingredients: oxygen & organic molecules broken down by intracellular enzymes, e.g.,  carbohydrates, fats, & proteins  Digestive tract  (gastrointestinal (GI) tract or alimentary canal) a muscular tube that extends from oral cavity to anus; passes  through pharynx, esophagus, stomach, & small & large intestines Functions of the Digestive System i. Ingestion  occurs when materials enter digestive tract via the mouth ii. Mechanical processing : crushing & shearing; materials easier to propel along digestive tract iii. Digestion : chemical breakdown of food into small organic fragments for absorption  iv. Secretion : release of water, acids, enzymes, buffers & salts by epithelium of digestive tract v. Absorption   is the movement of organic substrates, electrolytes, vitamins & water across digestive epithelium into  interstitial fluid of digestive tract vi. Excretion  is removal of waste products from body fluids Lining of the digestive tract protects against: corrosive effects of digestive acids & enzymes; mechanical stresses,  e.g., abrasion; bacteria ingested with food or that reside in digestive tract Digestive Organs & Peritoneum lined with serous membrane  1. Serosa (visceral peritoneum) covers organs within peritoneal cavity 2. Parietal peritoneum lines inner surfaces of body wall Peritoneal Fluid is produced by serous membrane lining & provides essential lubrication; separates parietal & visceral surfaces;  allows sliding without friction or irritation Mesenteries: double sheets of peritoneal membrane; suspend portions of digestive tract within peritoneal cavity by sheets of  serous membrane; connect parietal & visceral peritoneum  Areolar tissue  between mesothelial surfaces provides an access route to & from GI tract for passage of blood vessels, nerves &  lymphatic vessels; stabilize positions of attached organs & prevents intestines from becoming entangled Greater Omentum hangs from borders of stomach; adipose tissue in greater omentum conforms to shapes of surrounding organs  & pads & protects surfaces of abdomen; provides insulation to reduce heat loss & stores lipid energy reserves Mesentery Proper  is a thick mesenterial sheet that provides stability & permits some independent movement; it suspends all  but first 10 inches of small intestine Mesocolon – a mesentery associated with a portion of the large intestine
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