L44_NPB_101 - Lecture 44 •  SmartSite: – ...

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Unformatted text preview: Lecture 44 •  SmartSite: –  Lecture 44 Notes •  GastrointesCnal System –  Review: Anatomy –  Saliva –  Stomach –  Small IntesCnes •  Announcements: –  None •  Reading (Recommended): –  Ch 16 (pg. 588 ­638) 1 Review: DigesCve System •  •  •  •  MoClity SecreCon DigesCon AbsorpCon Table 16 ­1, pg. 592 2 Saliva •  Produced largely by three major pairs of salivary glands •  ComposiCon •  FuncCons –  –  –  –  –  –  –  –  –  99.5% H2O –  0.5% electrolytes and protein (amylase, mucus, lysozyme) Salivary amylase begins digesCon of carbohydrates Facilitates swallowing by moistening food Mucus provides lubricaCon AnCbacterial acCon Solvent for molecules that sCmulate taste buds Aids speech by facilitaCng movements of lips and tongue Helps keep mouth and teeth clean Rich in bicarbonate buffers •  Lysozyme destroys bacteria •  Saliva rinses away material that could serve as food source for bacteria 3 Stomach •  J ­shaped sac ­like chamber lying between esophagus and small intesCne •  Divided into three secCons –  Fundus –  Body –  Antrum •  Three main funcCons –  Store ingested food unCl it can be empCed into small intesCne –  Secretes hydrochloric acid (HCl) and enzymes that begin protein digesCon –  Mixing movements convert pulverized food to chyme •  Pyloric sphincter –  Serves as barrier between stomach and upper part of small intesCne 4 Stomach Fig. 16 ­7, pg. 601 5 Gastric MoClity •  Filling –  Involves recepCve relaxaCon •  Enhances stomach’s ability to accommodate the extra volume of food with liale rise in stomach pressure •  Triggered by act of eaCng •  Mediated by vagus nerve •  Storage •  Mixing –  Takes place in body of stomach –  Takes place in antrum of stomach –  Largely controlled by factors in duodenum 6 •  Emptying Gastric Emptying and Mixing as a Result of Antral PeristalCc ContracCons Fig. 16 ­8, pg. 602 7 Gastric Emptying •  Factors in stomach •  Factors in duodenum –  Fat –  Amount of chyme in stomach is main factor that influences strength of contracCon –  Acid •  Fat digesCon and absorpCon takes place only within lumen of small intesCne •  When fat is already in duodenum, further gastric emptying of addiConal faay stomach contents is prevented •  Unneutralized acid in duodenum inhibits further emptying of acidic gastric contents unCl neutralizaCon can be accomplished •  Gastric emptying is reflexly inhibited when osmolarity of duodenal contents starts to rise •  Too much chyme in duodenum inhibits emptying of even more gastric contents 8 –  Hypertonicity –  Distension Gastric SecreCons •  Two disCnct areas of gastric mucosa that secrete gastric juice –  OxynCc mucosa –  Pyloric gland area (PGA) •  Lines the antrum •  Lines body and fundus •  Gastric pits at base of gastric glands •  Three types of gastric exocrine secretory cells –  Mucous cells –  Chief cells •  Line gastric pits and entrance of glands •  Secrete thin, watery mucus •  Secrete enzyme precursor, pepsinogen •  Secrete HCl and intrinsic factor –  Parietal (oxynCc) cells 9 Gastric SecreCons Table 16 ­3, pg. 606 10 Gastric Glands Table 16 ­3, pg. 606 11 Parietal Cell HCl SecreCon •  FuncCons of stomach acid (HCl) –  AcCvates pepsinogen to acCve enzyme pepsin and provides acid medium for opCmal pepsin acCvity –  Aids in breakdown of connecCve Cssue and muscle fibers –  Denatures protein –  Along with salivary lysozyme, kills most of the microorganisms ingested with food Fig. 16 ­9, pg. 607 12 Chief Cells Produce DigesCve Enzymes Fig. 16 ­10, pg. 608 13 Phases of Gastric SecreCon •  Cephalic phase –  Refers to increased secreCon of HCl and pepsinogen that occurs in response to sCmuli acCng in the head before food reaches stomach –  Begins when food actually reaches the stomach –  Presence of protein increases gastric secreCons –  Inhibitory phase –  Helps shut off flow of gastric juices as chyme begins to empty into small intesCne 14 •  Gastric phase •  IntesCnal phase Gastric Mucosal Barrier •  Enables stomach to contain acid without injuring itself Fig. 16 ­11, pg. 611 15 Stomach DigesCon •  Carbohydrate digesCon conCnues in body of the stomach. •  Protein digesCon begins in the antrum of the stomach. 16 Stomach AbsorpCon •  No food or water is absorbed into the blood through the stomach mucosa. •  Non ­nutrient absorpCon through the stomach mucosa: –  Aspirin –  Alcohol (more so in small intesCne) 17 Small IntesCne •  Site where most digesCon and absorpCon take place •  Three segments –  Duodenum –  Jejunum –  Ileum •  MoClity includes –  SegmentaCon –  MigraCng moClity complex Table 16 ­1, pg. 592 18 Small IntesCne •  SegmentaCon –  Primary method of moClity in small intesCne –  Consists of ring ­like contracCons along length of small intesCne –  Within seconds, contracted segments relax and previously relaxed areas contract –  AcCon mixes chyme throughout small intesCne lumen Fig. 16 ­19, pg. 621 19 Small IntesCne •  SegmentaCon –  iniCated by pacemaker cells in small intesCne which produce basic electrical rhythm (BER) –  Circular smooth muscle responsiveness is influenced by distension of intesCne, gastrin, and extrinsic nerve acCvity –  FuncCons •  Mixing chyme with digesCve juices secreted into small intesCne lumen •  Exposing all chyme to absorpCve surfaces of small intesCne mucosa •  MigraCng moClity complex –  Sweeps intesCnes clean between meals 20 Control of ileocecal valve/sphincter Fig. 16 ­20, pg. 622 21 ...
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