1. Digestive System

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

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

4. 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

5. 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

6. 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

7. 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

8. 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

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

10. 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

11. 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

12. 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 )
Plicae
Villi (Fig )
Microvilli on cells (Fig )
Goblet cells—produce mucus (Fig )
Crypts (Fig )

13. 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.

14. Liver Left lobe – 1/6th of liver Right lobe divided into three lobes
Right lobe proper
Caudate lobe
Quadrate lobe
Hepatic lobule (Figs , 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

15. 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

16. 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

17. 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 )
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

18. 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