Gastrointestinal Anatomy KAAP 310

Alimentary Canal and Accessory Organs 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 Functions Bounded by lips, cheeks, palate, and tongue Lined with stratified squamous epithelium Functions Ingestion Mechanical digestion Chemical digestion Propulsion

Oral Cavity, Pharynx, & Esophagus Oropharynx Laryngopharynx Hyoid Bone http://biology-forums.com/index.php?action=gallery;sa=view;id=8468

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 Upper esophageal sphincter Bolus Esophagus During the buccal phase, the upper esophageal sphincter is contracted. The tongue presses against the hard palate, forcing the food bolus into the oropharynx. 1 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. 2 The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after food enters. 3 Relaxed muscles Peristalsis moves food through the esophagus to the stomach. 4 The gastroesophageal sphincter surrounding the cardial oriface opens, and food enters the stomach. 5 Relaxed muscles Circular muscles contract Bolus of food Longitudinal muscles contract Circular muscles contract Gastroesophageal sphincter closed Gastroesophageal sphincter opens Stomach © 2013 Pearson Education, Inc.

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 Ileum 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 Liver Gallbladder Spleen 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 Anal canal Sphincters 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

Anal columns Pectinate line Anal sinuses Anus 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 Ingestion Propulsion Mechanical breakdown Digestion Absorption Defecation

Digestive Processes Ingestion Propulsion Mechanical breakdown 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 Segmentation mixes food with digestive juices and makes absorption more efficient by repeatedly moving different parts of the food mass over the intestinal wall. http://cnx.org/content/m46502/latest/2405_Digestive_Process.jpg

Ingestion Mechanical breakdown Digestion Propulsion Absorption Figure 23.2 Gastrointestinal tract activities. Ingestion Mechanical breakdown Digestion Propulsion Absorption Defecation Food Pharynx Esophagus Chewing (mouth) • Swallowing (oropharynx) • Peristalsis (esophagus, stomach, small intestine, large intestine) Stomach Lymph vessel Small intestine Large Blood Mainly H2O Feces Anus Churning (stomach) Segmentation (small intestine) © 2013 Pearson Education, Inc.

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) 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. Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving food forward then backward. Food mixing and slow food propulsion occur. © 2013 Pearson Education, Inc.