Digestion and Absorption of Carbohydrates Lipids Proteins The Gastrointestinal Tract physiology Mouth esophagus stomach small intestine large intestine Functions of GI Tract Makes nutrients available to cell via Digestion hydrolysis of nutrients food broken down Absorption passage of simple molecules across gut wall and into blood or lymph Elimination of wastes Protects body from harmful substances HCl in stomach antibacterial agent Metabolic processes Metabolism of food Organs of GI Tract GI Tract Lumen Mucosa innermost layer 3 layers Epithelial in contact w lumen contains endocrine hormone and exocrine enzyme glands Lamina Propria white blood cells Muscularis Mucosa Submucosa connective tissue carries white blood cells Network of nerves submucosa plexus Peristalsis wavelike movement mainly in esophagus Muscularis Externa layer where peristalsis occurs movement Serosa outermost layer DIGESTION the following are the steps of digestion I have included an overall summary table at the end of this portion of the study guide for easier memorization but know ALL steps and details Mouth oral cavity digestion of CHO begins here 3 salivary secreting glands parotid sublingual submandibular submaxillary Sublingual and Submandibular are the only ones secreting mucus lubricates and protects against acid and erosion 99 of saliva is H2O contains dissolving properties Saliva components water electrolytes mucus enzymes antibacterial antiviral compounds Enzymes Salivary amylase produced in salivary glands digestion of CHO hydrolyzes alpha 1 4 linkages Lingual lipase only activates in stomach fats short med chain triglycerides Lysozymes Mastication chewing breaks down food increases surface area kill bacteria Bolus ball from mixture of food and saliva Digestion of Starch Amylopectin alpha 1 4 linkages forms dextrin maltose glucose and glucose maltotriose maltose and glucose Dextrin contains 1 6 linkage harder to digest Amylase alpha 1 4 linkages forms maltotriose and maltose Esophagus bolus propelled through peristalsis Muscular tube connects back of mouth to stomach movement of food via peristalsis At top of esophagus some voluntary movement Upper esophageal sphincter opening at top to let food in Lower esophageal sphincter relaxes to let food into stomach Pressure in sphincter pressure in stomach Once pressure drops valve will open food will pass Constricts to keep food from moving back up into esophagus holds food secretes protein digesting enzymes and strong acids where protein digestion Stomach begins 3 types of muscle Circular longitudinal oblique diagonal Mechanical mixing and breakdown of food Formation of chyme bolus and gastric juices Gastric secretions Absorption of few fat soluble substances aspirin and alcohol 4 sections from top to bottom cardium fungus body distal antrum Rugae can flatten allows stomach to expand and hold more 4 types of cells in stomach in gastric juice Neck cells secrete mucus Enteroendocrine cells secrete hormones Chief pectic cells secrete enzymes gastric lipase pepsinogen Parietal cells Ach secretion and IP necessary for absorption of vitamin B12 Lipid Digestion in Stomach Lipids digested by lipase lingual lipase Only 20 of lipid digestion occurs in stomach rest occurs in small intestine pH in stomach low because of HCl acidity of HCl inactivates salivary amylase NO CARBOHYDRATE DIGESTION IN STOMACH Protein digestion in Stomach Protein hydrolysis to smaller peptides proteases peptones via pepsin produced in gastric glands released in stomach Pepsin is an endopeptidase break bonds within protein Exopeptidases break bonds in terminal end of proteins Pepsinogen zymogen inactive protein digesting enzyme proteolytic enzymes secreted in inactive form because they will destroy the Zymogens cells that produce them they are activated where needed Pepsinogen inactive form secreted in response to Ach by chief peptic cells Activation of pepsinogen by HCl and pepsin autocatalytic pepsin can activate pepsinogen as well Removal of peptide activates pepsinogen Activation produces pepsin active to act on protein hydrolyzes to smaller peptides HCl will act upon protein by denaturation BEFORE pepsin Uncoiling of protein H bonds disulfide bridges broken by HCl Bonds left open pepsin comes in and breaks these bonds Pepsinogen 1 2 produced in body of stomach 2 also produced in distal end Secreted by parietal cells even when stomach is empty Regulated by Gastrin Peptide hormone Release stimulated by presence of protein or by gastrin releasing peptide GRP or bombesin in response to Ach Secreted by enteroendorcine cells G cells in stomach small intestine proximal end duodenum HCl Regulated by Acetylcholine Released in response to local reflex of stomach distention Vagus nerve stimulated releases Ach Ach stimulates release of GRP which stimulates release of gastrin GRP also released by enteric nerves in GI tract Ach can also act directly on gastrin cells Ach can also act on parietal cells Regulated by Histamine Vasoactive Amine produced by mast cells Stimulated by vagus nerve and gastrin as well Like gastrin Ach has receptor on parietal cell Parietal cells have H2 receptors histamine will bind to form HCl Regulated by Somatostatin a hormone produced in stomach duodenum Inhibits HCl secretion Ach inhibits secretion of somatostatin whereas H promotes secretion High acidity high H ions secretion somatostatin negative feedback Gastrointestinal Reflux Disease heart burn GERD Due to reflux of digestive juices from stomach into esophagus Lower gastroesophageal Sphincter LES relaxed stomach pressure increase Relieved Prevented by antiacids decrease HCl production by Histamine 2 H2 blockers ex Pepcid AC Tagamet HB Zantac 75 Inhibit HCl by stopping the binding of histamine to parietal cells Proton pump inhibitors Nexium and Prilosec Inhibit hydrogen ions Aggravation of heartburn High acid Further decrease of LES pressure Irritate spices and citrus coffee caffeine alcohol calcium tea chocolate high fat foods peppermint alcohol Pyloric sphincter between stomach and duodenum Regulates food movement between stomach and small intestine Small intestine 3 sections Virtually all absorption and digestion occurs here Most absorption occurs in duodenum top portion of small intestine Duodenum jejunum ileum nutrient absorption Microvilli hairlike structures on villi increases amount of surface area available for On top of enterocyte cells absorptive intestinal cells brush border Within villi capillaries and
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