Digestive System

Role of the Digestive System Preparation of food for absorption Preparation of food for use in cell Elimination of unabsorbed food

Organs of Digestion Two basic groups of organs (See Fig. 25-1; Table 25-1) Gastrointestinal (GI) tract (or alimentary canal) Accessory organs

Wall of the GI Tract 3) Muscularis Layers –There are 4 layers of tissue (See Figure 25-2, page 741) 1) Mucosa – inner layer a) Mucous epithelium b) Lamina propria c) Muscularis mucosae 2) Submucosa a) Connective tissue b) Submucosal plexus 3) Muscularis a) Inner and outer layer of smooth muscle b) Myenteric plexus 4) Serosa a) Connective tissue layer b) Peritoneum

Modifications of the Layers Although all 4 layers are found through out, the walls vary based on their location in the digestive tract. See Table 25-2, page 742

Mouth – Structure of Oral Cavity Lips - Philtrum, Oral fissure Cheeks – lateral boundaries of oral cavity Hard palate consists of 4 bones: (2) maxilla and (2) palatine bone. (See Fig. 8-5, page 219 and Fig. 25-3, 743) Soft palate - between the mouth and nasopharynx Fauces (opening between mouth and oropharynx) Uvula Tongue – remember taste buds? Also see fig. 25-4, page 744 Lingual frenulum – Fold of mucous membrane in midline of the undersurface of the tongue – anchor the tongue to the floor of mouth Plica fimbriata - In this area the tongue is highly vascular and vessels are superficial; therefore, some drugs are placed under the tongue for rapid absorption

Salivary Glands – 3 pairs Parotid glands (Fig. 25-6) a. Drain via the parotid duct into the vestibule opposite upper second molars b. Secrete enzymes only (no mucus) Submandibular glands (Fig. 25-6) a. Ducts opening on either side of the lingual frenulum b. Secrete enzymes and mucus Sublingual glands (Fig. 25-6) a. Ducts open onto the floor of the mouth b. Secrete mucus only

Pharynx and Esophagus Pharynx (p. 747) Nasopharynx Oropharynx Laryngopharynx Esophagus (Fig. 25-9) Upper third—striated muscle Middle third—mixed striated and smooth muscle Lower third—smooth muscle

Stomach Size and position of the stomach Distensible Close to diaphragm In the epigastrium and left hypochondrium

Stomach – Figure 25-10, Page 749 Divisions of the stomach – Fundus, Body, Pylorus Curves of the stomach - Lesser curvature, Greater curvature Sphincter muscles - Cardiac sphincter, Pyloric sphincter Stomach Wall – Has the 4 layers, Note modification of Gastric Mucosa, and Gastric Muscle

Functions of the Stomach Serves as reservoir for food Secretes gastric juice (enzymes and acid) Mixes enzymes and chyme (through muscular action) and moves chyme into small intestine Secretes intrinsic factor (Protects vitamin B12 from acid and needed for absorption) Absorption (limited to certain drugs, some water, alcohol, and some fatty acids) Secretes hormone gastrin Destroys pathogenic bacteria See page 750

Small Intestines 20 feet long; fills most of abdominal cavity Divisions of the small intestine Duodenum—10 inches long Jejunum—8 feet long Ileum—12 feet long Wall of the small intestine (Fig. 25-13) Plicae Villi (Fig. 25-15) Microvilli on cells (Fig. 25-15) Goblet cells—produce mucus (Fig. 25-14) Crypts (Fig. 25-15)

Large Intestine 5 to 6 Feet Divisions of the large intestine Cecum—2 to 3 inches long, Appendix extending from it Colon a. Ascending colon b. Transverse colon - From hepatic flexure to splenic flexure c. Descending colon d. Sigmoid colon Rectum —7 to 8 inches long; terminal inch called anal canal. Anal columns are vertical folds and containing hemorrhoidal arteries and veins. Hemorrhoids formed by enlarged veins.

Liver Left lobe – 1/6th of liver Right lobe divided into three lobes Right lobe proper Caudate lobe Quadrate lobe Hepatic lobule (Figs. 25-23, page 758) – Anatomical units of the liver. Hepatic lobule function (page 759) With the hepatic cells are many phagocytic reticuloendothelial cells. These cells remove bacteria, worn RBCs, etc. from the blood Hepatic cells remove and store some vitamins Hepatic cells detoxify poisons Hepatic cells form bile

Liver Function Detoxification Bile secretion Metabolism of food Storage of iron and vitamins A, B12, and D Production of some plasma proteins Site of fetal hematopoiesis

Gallbladder (p 760) 3 to 4 inches long, 1 inch wide Capacity: 30 to 50 ml of bile Located under the liver Structure of the gallbladder Mucosa—(rugae) Muscularis Serosa Functions of the gallbladder Storage of bile Concentration of bile

Pancreas – p. 761 About 6 to 9 inches long Located between the stomach and the duodenum Sections of the pancreas Head of the pancreas to the right, against the duodenum Body in between the stomach and the duodenum Tail extending to the left Structure of the pancreas (Fig. 25-27) Exocrine portion (compound acinar cells) Produces digestive enzymes Endocrine portion—pancreatic islets - About a million islets Functions of the pancreas Acinar units secrete digestive enzymes Beta cells of pancreatic islets secrete insulin Alpha cells of pancreatic islets secrete glucagon

Disorders of Digestive System Mumps – viral disease characterized by swelling of the parotid salivary glands. Tooth Decay, Gingivitis, Periodontitis, Maloccusion Gastroesophageal Reflux Disease (GERD) Ulcers Appendicitis Hemorrhoids See pages 764 to 766