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HUN3224 Intermediate Metabolism of Nutrients I Exam I Study Guide I Digestion and Absorption of Carbohydrates Lipids and Proteins A Physiology of the gastrointestinal GI tract 1 List the parts of the GI tract in the proper sequence and not the purpose function of each Also list the accessory organs and their purpose function in relation to digestion and absorption o main structures of GI tract include the oral cavity esophagus and stomach collectively referred to as upper and the small and large intestines lower GI o Accessory organs pancreas liver and gallbladder o Accessory organs provide or store secretions that ultimately are delivered to the lumen of the digestive tract and aid in the digestive and absorptive processes o Interior passageway of GI tract lumen has four main tunics o Mucosa submucosa muscularis externa serosa or adventitia mouth and pharynx consitute the oral cavity and provide entrance to o 1 Oral cavity digestive tract o Major enzyme alpha amylase also called ptyalin Second digestive enzyme lingual lipase Hydrolyzes dietary triacylglycerols in stomach Mucus lubricates food and protects oral mucosa Antibacterial and antiviral compounds IgA and other solutes are also in saliva o 2 Esophagus o Muscular tube from mouth food now mixed with saliva bolus Connects the back of the mouth and stomach Movement of food via peristalsis o Lower esophageal sphincter circular muscular valve Relaxes to let food into the stomach o 3 Stomach Constricts to keep food from moving back up into esophagus once the bolus of food has passed through gastroesophageal sphincter it enters the stomach a J shaped organ located on left side of abdomen under diaphragm o Holds food o Mechanical mixing and breaking down of food o Gastric secretion o Absorption of alcohol and aspirin o Stomach has four main regions cardia region fundus body and antrum or distal pyloric portion main stie for nutrient digestion and absorption The antrum grinds and mixes food with gastric juices thus forming a semi liquid chyme also provides strong peristalsis for gastric emptying pyloric sphincter into the duodenum Stomach begins mixing food with gastric juices and enzymes When the stomach is empty folds rugae present in all but antrum section of the stomach are visible however when stomach is full rugae disappear Gastric juices are secreted by three different glands Cardiac glands oxyntic glands pyloric glands o 4 Small Intestine Three sections duodenum jejunum Ileum Digestion in Small intestine Digestive events occur o 5 Large Intestine Colon large intestine In the lumen Absorption of water and electrolytes Microorganisms act on energy nutrients not previously digested absorbed in S I to form Gases o Ex CO2 methane hydrogen lobes Accessory Organs o 1 Pancreas facilitate digestive and absorptive processes in the small intestine two types of cells in pancreas 1 ductless endocrine cells that secrete hormones primarily insulin and glucagon and 2 acinar exocrine cells that produce the digestive enzymes which get packed in secretory structures called granules and released by exocytosis into pancreatic juice contains bicarbonate Pancreatic juice produced by acinar cells neutralizes acid chyme passing into duodenum from stomach electrolytes and pancreatic digestive enzymes in a watery solution largest single internal organ of the body is made up of right and left o 2 Liver Lobes have functional units called lobules made up of sheets or plates of liver cells called hepatocytes o 3 Gallbladder the gallbladder is located on the surface of the liver Gallbladder concentrates and stores the bile made in the liver until it is needed for fat digestion in the small intestine hormone cholecystokinin secreted into blood by enteroendocrine cells of proximal small intestine stimulates gallbladder to contract and release bile into duodenum Somatostatin works in paracrine fashion inhibits gallbladder contraction 2 Describe how the epithelial lining of the small intestine is structured to enhance surface area to facilitate nutrient absorption o The small intestine is structured to maximize surface area and thus maximize its ability to absorb nutrients The small intestine has a surface area of approximately 300m 2 Structures contributing to surface area o Large circular folds of mucosa called folds of Kerckring protrude into lumen o Villi that project out into lumen enterocytes absorptive epithelial cells o Microvilli hairline extensions of plasma membrane of the enterocytes that make up the villi B Digestion 1 For each energy nutrient a Identify major site s of digestion b Identify major end products of digestion c Describe the sequence of events in the digestion of each energy nutrient being certain to 1 Name the enzymes involved 2 Describe the function of each enzyme 3 identify the source of the enzyme e g pancreas 4 And identify the site of action for the enzyme e g lumen of S I d Note the role of such factors as pH hormones and end product concentration in controlling the synthesis and or activity of these digestive enzymes 1 Lipids digestive enzymes involved in breaking down dietary lipids in gastrointestinal tract are estrases that cleave the ester bonds within triacylglycerols lipase phospholipids phospholipases and cholesteryl esters cholesterol esterase o Most digestion is completed in lumen of small intestine although process begins in stomach with lingual lipase and gastric lipase o Gastric lipase readily penetrates milk fat globules without substrate stabilization by bile salts o Both lingual lipase and gastric lipase hydrolyze fatty acids preferably at the sn 3 position releasing a fatty acid and 1 2 diacyglycerols as products Shorter chains are metabolized more directly than long chains o For dietary fat in stomach to be hydrolyzed by lingual and gastric lipases some degree of emulsification must occur to expose a sufficient surface area of the substrate o Muscle contractions of stomach and squirting of fat through partially opened pyloric sphincter produce shear forces for sufficient emulsification o Presence of undigested lipids in stomach delay stomach emptying o Lipids limited hydrolysis via lingual gastric lipase Gastric lipase hydrolyzes short and medium chain triacylglycerols and is responsible for 20 lipid digestion in humans 2 Proteins o PTN digestion in stomach o Secretion of pepsinogen By chief peptic cells mainly in response to acetylcholine acetylcholine is released from vagus nerve for action on parietal


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FSU HUN 3224 - Exam I

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Notes

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24 pages

LIPIDS

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Exam 1

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Exam 2

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