Gastrointestinal Anatomy KAAP 310 Alimentary Canal and Accessory Organs • Alimentary Canal: – – – – – – – Mouth (oral cavity) Pharynx Esophagus Stomach Small intestine Large intestine Anus • Accessory Organs*: – – – – – Tongue Salivary Glands Liver Pancreas Gall bladder http://1.bp.blogspot.com/-JcKROgygeKo/UW4PTqKCiII/AAAAAAAABxg/g0UShGYLiYc/s1600/digestive+system.jpg Mouth • Oral (buccal) cavity – Bounded by lips, cheeks, palate, and tongue – Lined with stratified squamous epithelium • Functions – Ingestion – Mechanical digestion – Chemical digestion – Propulsion Oral Cavity, Pharynx, & Esophagus Oropharynx Hyoid Bone http://biology-forums.com/index.php?action=gallery;sa=view;id=8468 Laryngopharynx Pharynx • Throat, passes air and food via sequential contraction of muscles Esophagus • Carries food from throat to stomach, collapsed when empty • Diaphragm and esophageal sphincter (and gravity) keep food in stomach Figure 23.13 Deglutition (swallowing). Slide 1 Bolus of food Tongue Uvula Pharynx Bolus Epiglottis Epiglottis Glottis Trachea Esophagus 1 During the buccal phase, the upper esophageal sphincter is contracted. The tongue presses against the hard palate, forcing the food bolus into the oropharynx. 2 The pharyngeal-esophageal phase begins as the uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. 4 Peristalsis moves food through the esophagus to the stomach. Relaxed muscles Circular muscles contract Upper esophageal sphincter 3 The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after food enters. Relaxed muscles 5 The gastroesophageal sphincter surrounding the cardial oriface opens, and food enters the stomach. Bolus of food Longitudinal muscles contract Circular muscles contract Gastroesophageal sphincter closed Gastroesophageal sphincter opens Stomach © 2013 Pearson Education, Inc. Bolus Stomach http://apbrwww5.apsu.edu/thompsonj/Anatomy%20&%20Physiology/2020/2020%20Exam%20Reviews/Exam%203/stomach%20diagram.jpg Stomach • Mechanical breakdown • Denaturation of proteins by HCl • Enzymatic digestion of proteins by pepsin (and milk protein by rennin in infants) • Delivers chyme to small intestine • Lipid-soluble alcohol and aspirin absorbed into blood • Secretion of intrinsic factor for vitamin B12 absorption • Only stomach function essential for life • B12 needed mature red blood cells Small Intestine http://www.cea1.com/wp-content/uploads/2013/08/Small-Intestine-Duodenum.jpg Small Intestine • Major organ of digestion and absorption • 2-4 m long; from pyloric sphincter to illeocecal valve • Subdivisions – Duodenum (retroperitoneal) – Jejunum (attached posteriorly by mesentery) – Ileum (attached posteriorly by mesentery) Duodenum • Curves around head of pancreas; shortest part – 25 cm • Bile duct (from liver) and main pancreatic duct (from pancreas) Jejunum & Illeum • Jejunum – Extends from duodenum to ileum – About 2.5 m long • Ileum – Joins large intestine at illeocecal valve – About 3.6 m long Digestion in Small Intestines • Chyme from stomach contains – Partially digested carbohydrates and proteins – Undigested fats • 3–6 hours in small intestine – Most water absorbed – ~ All nutrients absorbed • Small intestine, like stomach, no role in ingestion or defecation Large Intestine • Cecum – first part of large intestine • Appendix – masses of lymphoid tissue – Part of MALT of immune system – Bacterial storehouse recolonizes gut when necessary – Twisted enteric bacteria accumulate and multiply Large Intestine • Retroperitoneal except for transverse and sigmoid regions • Ascending colon (right side – to level of right kidney) right colic (hepatic) flexure • Transverse colon left colic (splenic) flexure • Descending colon (left side) • Sigmoid colon in pelvis rectum Large Intestine Anus http://test.classconnection.s3.amazonaws.com/232/flashcards/464232/png/large_intestine.png Digestion in Large Intestine • Residue remains in large intestine 12–24 hours • No food breakdown except by enteric bacteria • Vitamins (made by bacterial flora), water, and electrolytes (especially Na+ and Cl–) reclaimed • Major functions - propulsion of feces to anus; defecation • Colon not essential for life Accessory Organs Liver http://safetyca.info/wp-content/uploads/2013/06/pancreas-accessory-organthe-digestive-system-atxrijk1.jpg Accessory Organs • Pancreas – Endocrine function • Pancreatic islets secrete insulin and glucagon – Exocrine function • Acini (clusters of secretory cells) secrete pancreatic juice – To duodenum via main pancreatic duct • Liver – Many functions; only digestive function bile production • Bile – fat emulsifier • Gallbladder – Chief function bile storage • Spleen Rectum and Anus • Rectum – Three rectal valves stop feces from being passed with gas (flatus) • Anal canal – Last segment of large intestine – Opens to body exterior at anus • Sphincters – Internal anal sphincter—smooth muscle – External anal sphincter—skeletal muscle Figure 23.29b Gross anatomy of the large intestine. Rectal valve Rectum Hemorrhoidal veins Levator ani muscle Anal canal External anal sphincter Internal anal sphincter Anal columns Pectinate line Anal sinuses Anus © 2013 Pearson Education, Inc. Digestive Processes • Six essential activities 1. 2. 3. 4. 5. 6. Ingestion Propulsion Mechanical breakdown Digestion Absorption Defecation Digestive Processes Ingestion • Bringing food in via the mouth Propulsion • • Swallowing – voluntary Peristalsis – involuntary contraction and relaxation of muscles in organ walls Mechanical breakdown • Chewing, mixing food with saliva, churning food in stomach, and segmentation – rhythmic local constrictions of the small intestine Digestion • Enzymes break down complex food molecules to their chemical building blocks Absorption • Passage of digested end products from the lumen of the GI tract into the blood or lymph Defecation • Elimination of indigestible substances from the body via the anus http://cnx.org/content/m46502/latest/2405_Digestive_Process.jpg Figure 23.2 Gastrointestinal tract activities. Ingestion Mechanical breakdown • Chewing (mouth) • Churning (stomach) • Segmentation (small intestine) Digestion Food Pharynx Esophagus Propulsion • Swallowing (oropharynx) • Peristalsis (esophagus, stomach, small intestine, large intestine) Stomach Absorption Lymph vessel Small intestine Large intestine Blood vessel Mainly H2O Feces Defecation © 2013 Pearson Education, Inc. Anus Functions of Gastrointestinal Organs Mouth – Ingestion, propulsion, mechanical breakdown, digestion Pharynx & Esophagus – Propulsion Stomach – Propulsion, mechanical breakdown, digestion, absorption Small Intestine & associated accessory organs (liver, gallbladder, pancreas) – Propulsion, mechanical breakdown, digestion, absorption Large Intestine – Digestion, absorption, propulsion, defecation Figure 23.3 Peristalsis and segmentation. From mouth Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, moving food along the tract distally. © 2013 Pearson Education, Inc. Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving food forward then backward. Food mixing and slow food propulsion occur.