ANATOMY & PHYSIOLOGY Chapter 23 THE DIGESTIVE SYSTEM PowerPoint Image Slideshow

O VERVIEW OF THE D IGESTIVE S YSTEM

© 2013 Pearson Education, Inc. Figure 23.1 Alimentary canal and related accessory digestive organs. Mouth (oral cavity) Tongue* Esophagus Liver* Gallbladder* Small intestine Salivary glands* Pharynx Stomach Pancreas* Large intestine (Spleen) Parotid gland Sublingual gland Submandibular gland Duodenum Jejunum Ileum Anus Transverse colon Descending colon Ascending colon Cecum Sigmoid colon Rectum Appendix Anal canal

© 2013 Pearson Education, Inc. DIGESTIVE PROCESSES Six essential activities 1.Ingestion 2.Propulsion 3.Mechanical breakdown 4.Digestion 5.Absorption 6.Defecation

© 2013 Pearson Education, Inc. 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 intestine Blood vessel Mainly H 2 O Feces Anus Churning (stomach) Segmentation (small intestine)

© 2013 Pearson Education, Inc. GI TRACT REGULATORY MECHANISMS 1.Mechanoreceptors and chemoreceptors Respond to stretch, changes in osmolarity and pH, and presence of substrate and end products of digestion Initiate reflexes that Activate or inhibit digestive glands Stimulate smooth muscle to mix and move lumen contents 2.Intrinsic and extrinsic controls Short reflexes - enteric nerve plexuses (gut brain) respond to stimuli in GI tract Long reflexes respond to stimuli inside or outside GI tract; involve CNS centers and autonomic nerves Hormones from cells in stomach and small intestine stimulate target cells in same or different organs to secrete or contract

© 2013 Pearson Education, Inc. Figure 23.4 Neural reflex pathways initiated by stimuli inside or outside the gastrointestinal tract. External stimuli (sight, smell, taste, thought of food) Visceral afferents Internal (GI tract) stimuli Chemoreceptors, osmoreceptors, or mechanoreceptors Long reflexes Central nervous system Local (intrinsic) nerve plexus ("gut brain") Effectors: Smooth muscle or glands Extrinsic visceral (autonomic) efferents Short reflexes Lumen of the alimentary canal Gastrointestinal wall (site of short reflexes) Response: Change in contractile or secretory activity

FIGURE 23.7 Mouth The mouth includes the lips, tongue, palate, gums, and teeth.

FIGURE 23.8 Tongue This superior view of the tongue shows the locations and types of lingual papillae.

FIGURE 23.9 Salivary glands The major salivary glands are located outside the oral mucosa and deliver saliva into the mouth through ducts.

FIGURE Permanent and Deciduous Teeth This figure of two human dentitions shows the arrangement of teeth in the maxilla and mandible, and the relationship between the deciduous and permanent teeth.

FIGURE The Structure of the Tooth This longitudinal section through a molar in its alveolar socket shows the relationships between enamel, dentin, and pulp.

FIGURE Pharynx The pharynx runs from the nostrils to the esophagus and the larynx.

FIGURE Esophagus The upper esophageal sphincter controls the movement of food from the pharynx to the esophagus. The lower esophageal sphincter controls the movement of food from the esophagus to the stomach.

FIGURE Deglutition Deglutition includes the voluntary phase and two involuntary phases: the pharyngeal phase and the esophageal phase.

FIGURE Stomach The stomach has four major regions: the cardia, fundus, body, and pylorus. The addition of an inner oblique smooth muscle layer gives the muscularis the ability to vigorously churn and mix food.

FIGURE Histology of the Stomach The stomach wall is adapted for the functions of the stomach. In the epithelium, gastric pits lead to gastric glands that secrete gastric juice. The gastric glands (one gland is shown enlarged on the right) contain different types of cells that secrete a variety of enzymes, including hydrochloride acid, which activates the protein-digesting enzyme pepsin.

FIGURE The Three Phases of Gastric Secretion Gastric secretion occurs in three phases: cephalic, gastric, and intestinal. During each phase, the secretion of gastric juice can be stimulated or inhibited.

FIGURE Small Intestine The three regions of the small intestine are the duodenum, jejunum, and ileum.

FIGURE Histology of the Small Intestine (a) The absorptive surface of the small intestine is vastly enlarged by the presence of circular folds, villi, and microvilli. (b) Micrograph of the circular folds. (c) Micrograph of the villi. (d) Electron micrograph of the microvilli. From left to right, LM × 56, LM × 508, EM × 196,000. (credit b-d: Micrograph provided by the Regents of University of Michigan Medical School © 2012)

FIGURE Segmentation Segmentation separates chyme and then pushes it back together, mixing it and providing time for digestion and absorption.

FIGURE Large Intestine The large intestine includes the cecum, colon, and rectum.

FIGURE Histology of the large Intestine (a)The histologies of the large intestine and small intestine (not shown) are adapted for the digestive functions of each organ. (b)This micrograph shows the colon’s simple columnar epithelium and goblet cells. LM × 464. (credit b: Micrograph provided by the Regents of University of Michigan Medical School © 2012)

FIGURE Teniae Coli, Haustra, and Epiploic Appendages

FIGURE Accessory Organs The liver, pancreas, and gallbladder are considered accessory digestive organs, but their roles in the digestive system are vital.

FIGURE Microscopic Anatomy of the Liver The liver receives oxygenated blood from the hepatic artery and nutrient-rich deoxygenated blood from the hepatic portal vein.

FIGURE Exocrine and Endocrine Pancreas The pancreas has a head, a body, and a tail. It delivers pancreatic juice to the duodenum through the pancreatic duct.

FIGURE Gallbladder The gallbladder stores and concentrates bile, and releases it into the two-way cystic duct when it is needed by the small intestine.

FIGURE Digestion and Absorption Digestion begins in the mouth and continues as food travels through the small intestine. Most absorption occurs in the small intestine.

FIGURE Carbohydrate Digestion Flow Chart Carbohydrates are broken down into their monomers in a series of steps.

FIGURE Digestion of Protein The digestion of protein begins in the stomach and is completed in the small intestine.

FIGURE Digestion of Protein Flow Chart Proteins are successively broken down into their amino acid components.

FIGURE Digestive Secretions and Absorption of Water Absorption is a complex process, in which nutrients from digested food are harvested.

FIGURE Lipid Absorption Unlike amino acids and simple sugars, lipids are transformed as they are absorbed through epithelial cells.

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