Transcript Power Point: Digestion

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
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