Digestive System Chapter 16 2016 by Elsevier Inc

Learning Objectives Lesson 16. 1: Digestive System 1. 2. 3. List and describe the four layers of the wall of the alimentary canal. Compare the lining layer in the esophagus, stomach, small intestine, and large intestine. Define and contrast mechanical and chemical digestion. Discuss the basics of carbohydrate, protein, and fat digestion and give the end products of each process. © 2016 by Elsevier Inc. All rights reserved. 2

Learning Objectives Lesson 16. 1: Digestive System (Cont. ) 4. 5. List in sequence each of the component parts or segments of the alimentary canal from the mouth to the anus and identify the accessory organs of digestion. Define peristalsis, bolus, chyme, jaundice, ulcer, and diarrhea. © 2016 by Elsevier Inc. All rights reserved. 3

Overview of Digestion Principle structure of digestive system: Irregular tube called alimentary canal or gastrointestinal (GI) tract and accessory organs of digestion Food must first be digested and absorbed © 2016 by Elsevier Inc. All rights reserved. 4

Location of Digestive Organs © 2016 by Elsevier Inc. All rights reserved. 5

Organs of the Digestive System © 2016 by Elsevier Inc. All rights reserved. 6

Overview of Digestion (Cont. ) Ingestion Ø Complex foods taken into the GI tract Digestion Ø Group of processes that break complex nutrients into simpler ones • Mechanical digestion • Chemical digestion Breaks large chunks of food into smaller bits Breaks large molecules into smaller ones Motility Ø A number of GI movements resulting from muscular contraction © 2016 by Elsevier Inc. All rights reserved. 7

Overview of Digestion (Cont. ) Secretion Ø Absorption Ø Release of digestive juices and hormones that facilitate digestion Movement of digested nutrients into the internal environment of the body Regulation Ø Neural, hormonal, and other mechanisms that regulate digestive activity © 2016 by Elsevier Inc. All rights reserved. 8

Wall of the Digestive Tract Digestive tract described as tube that extends from mouth to anus Wall formed by four layers of tissue 1. Mucosa or mucous membrane • • 2. Type varies depending on GI location (tough and stratified or delicate and simple epithelium) Mucus production Submucosa • Connective tissue layer © 2016 by Elsevier Inc. All rights reserved. 9

Wall of the Digestive Tract (Cont. ) Wall formed by four layers of tissue 3. Muscularis • Circular, longitudinal, and oblique (in stomach) layers of muscle important in GI motility 4. Peristalsis: Wavelike movement pushes food down the tract (Figure 16 -3) Segmentation: “Back-and-forth” movement (Figure 16 -4) Serosa • • Serous membrane that covers outside of abdominal organs Attaches digestive tract to wall of abdominopelvic cavity by forming folds called mesenteries © 2016 by Elsevier Inc. All rights reserved. 10

Section of the Small Intestine © 2016 by Elsevier Inc. All rights reserved. 11

Peristalsis © 2016 by Elsevier Inc. All rights reserved. 12

Segmentation © 2016 by Elsevier Inc. All rights reserved. 13

Mouth: Structure of Oral Cavity Roof: Formed by hard palate (parts of maxillary and palatine bones) and soft palate, an archshaped muscle separating mouth from pharynx Uvula: Downward projection of soft palate (Figure 16 -5, A) Floor: Formed by tongue and its muscles Papillae: Small elevations on mucosa of tongue; taste buds, found in many papillae Lingual frenulum: Fold of mucous membrane that helps anchor tongue to floor of mouth (Figure 16 -5, C) © 2016 by Elsevier Inc. All rights reserved. 14

Mouth Cavity and Tongue C: From Zitelli BJ, Davis HW: Atlas of pediatric physical

Mouth: Teeth Typical tooth (Figure 16 -6) Ø Three main parts • • •

Longitudinal Section of a Tooth © 2016 by Elsevier Inc. All rights reserved. 17

Mouth: Teeth (Cont. ) Types of teeth Ø Ø Set of 20 teeth called deciduous or baby teeth Ø Incisors Canines or cuspids Premolars or bicuspids Molars or tricuspids Average cutting first tooth ~6 months old; set complete at ~30 months old Set of 32 permanent teeth Ø Average to cut first permanent tooth ~6 years old; set complete usually between 17 and 24 years old (Figure 16 -5, B) © 2016 by Elsevier Inc. All rights reserved. 18

Mouth: Salivary Glands Saliva Ø Ø Exocrine gland secretion flows into ducts Serous-type saliva: Watery and contains enzymes (salivary amylase) but no mucus • Ø Mucous-type saliva: Thick, slippery and contains mucus but no enzymes • • Produced by serous-type secretory cells (Figure 16 -7, B) Lubricates food during mastication Produced by mucus-type secretory cells (Figure 16 -7, B) Parotid glands (Figure 16 -7) Ø Ø Ø Largest salivary glands Produces serous type saliva Mumps: Infection of parotids © 2016 by Elsevier Inc. All rights reserved. 19

Mouth: Salivary Glands (Cont. ) Submandibular glands (Figure 16 -7, A) Ø Ø Ø Mixed gland: Produces both serous-type and mucous-type saliva (Figure 16 -7, B) Located below mandibular angle Ducts open on either side of lingual frenulum Sublingual glands (Figure 16 -7) Ø Ø Produce only mucous-type saliva Multiple ducts open into floor of mouth © 2016 by Elsevier Inc. All rights reserved. 20

Salivary Glands © 2016 by Elsevier Inc. All rights reserved. 21

Pharynx Three anatomic components Ø Ø Ø Nasopharynx Oropharynx Laryngopharynx Oropharynx most involved segment in digestive process of swallowing or deglutition Regulation of deglutition movements via motor cortex of cerebrum (voluntary) and “deglutition center” of brainstem (involuntary) © 2016 by Elsevier Inc. All rights reserved. 22

Pharynx © 2016 by Elsevier Inc. All rights reserved. 23

Esophagus Connects pharynx to stomach Dynamic passageway for food Upper esophageal sphincter (UES) Ø Helps prevent air from entering tube during respiration Lower esophageal sphincter (LES) Ø Food enters stomach by passing through LES or cardiac sphincter © 2016 by Elsevier Inc. All rights reserved. 24

Stomach Size Ø Expands after large meal; about size of large sausage when empty Food enters stomach through (cardiac) sphincter Pyloric sphincter muscle closes opening between pylorus (lower part of stomach) and duodenum © 2016 by Elsevier Inc. All rights reserved. 25

Stomach (Cont. ) Wall Ø Many smooth muscle fibers; contractions produce churning movements (peristalsis) Lining Ø Mucous membrane; many microscopic glands that secrete gastric juice and hydrochloric acid into stomach; mucous membrane lies in folds (rugae) when stomach is empty © 2016 by Elsevier Inc. All rights reserved. 26

Stomach (Cont. ) © 2016 by Elsevier Inc. All rights reserved. 27

Small Intestine Size Ø About 7 meters (20 feet) long but only 2 cm

Small Intestine © 2016 by Elsevier Inc. All rights reserved. 29

Small Intestine (Cont. ) Wall Ø Contains smooth muscle fibers that contract to produce peristalsis and segmentation movements Lining Ø Ø Ø Mucous membrane Many microscopic glands (intestinal glands) secrete intestinal juice Villi (microscopic finger-shaped projections from surface of mucosa into intestinal cavity) contain blood and lymph capillaries © 2016 by Elsevier Inc. All rights reserved. 30

Liver and Gallbladder Size and location Ø Liver is largest gland; fills upper right section of abdominal cavity and extends over into left side Liver secretes bile Ducts (Figure 16 -11) Ø Hepatic • Ø Cystic • Ø Drains bile from liver Duct by which bile enters and leaves gallbladder Common bile • • Formed by union of hepatic and cystic ducts Drains bile from hepatic or cystic ducts into duodenum © 2016 by Elsevier Inc. All rights reserved. 31

Liver and Gallbladder (Cont. ) Gallbladder Ø Location • Ø Undersurface of the liver

Gallbladder and Bile Ducts © 2016 by Elsevier Inc. All rights reserved. 33

Pancreas Exocrine gland that lies behind stomach Pancreatic cells secrete pancreatic juice (most important digestive juice) into pancreatic ducts; main duct empties into duodenum Pancreatic islets, or islets of Langerhans Ø Cells not connected with pancreatic ducts; secrete hormones glucagon and insulin into the blood © 2016 by Elsevier Inc. All rights reserved. 34

Large Intestine Divisions Ø Ø Cecum Colon: Ascending, transverse, descending, and sigmoid rectum Food enters through ileocecal valve; external opening called anus Wall Ø Contains smooth muscle fibers that contract to produce churning, peristalsis, and defecation Lining Ø Mucous membrane © 2016 by Elsevier Inc. All rights reserved. 35

Divisions of the Large Intestine © 2016 by Elsevier Inc. All rights reserved. 36

Appendix Vermiform appendix: Wormlike, tubular structure Appendix directly attached to back of cecum Ø Contains blind, tubelike interior lumen that communicates with lumen of large intestine No important digestive functions in humans © 2016 by Elsevier Inc. All rights reserved. 37

Peritoneum Location Ø Ø Continuous serous membrane lining abdominal cavity and covering abdominal organs Parietal layer: Lines abdominal cavity Visceral layer: Covers abdominal organs Peritoneal space: Small space between parietal and visceral layers © 2016 by Elsevier Inc. All rights reserved. 38

Peritoneum (Cont. ) Extensions Ø Ø Mesentery: Extension of parietal peritoneum, which attaches most of small intestine to posterior abdominal wall Greater omentum (lace apron): Hangs down from lower edge of stomach and transverse colon over intestines X-ray studies of the GI tract Ø Radiopaque contrast medium used to help visualize structures in study images © 2016 by Elsevier Inc. All rights reserved. 39

Peritoneum © 2016 by Elsevier Inc. All rights reserved. 40

Digestion Overview of digestion Ø Ø Transforms foods into substances that can be absorbed and used by cells Mechanical digestion • Ø Chewing (mastication), swallowing (deglutition), and peristalsis break food into tiny particles, mix them well with digestive juices, and move them along the digestive tract Chemical digestion • Breaks up large food molecules into compounds that have smaller molecules; brought about by digestive enzymes (Figure 16 -15) © 2016 by Elsevier Inc. All rights reserved. 41

Digestion (Cont. ) Carbohydrate digestion Ø Ø Occurs mainly in small intestine Pancreatic enzyme (amylase) • Ø Breaks down polysaccharides (starches) to disaccharides (double sugars) Intestinal juice enzymes • Maltase • Sucrase • Digests maltose (malt sugar) Digests sucrose (ordinary cane sugar) Lactase Digests lactose (milk sugar) © 2016 by Elsevier Inc. All rights reserved. 42

Digestion (Cont. ) Protein digestion Ø Ø Starts in stomach; completed in small intestine Pepsin • Ø Trypsin • Ø Gastric juice enzyme that partially digests proteins Pancreatic enzyme that continues digestion of proteins Peptidases • Intestinal enzymes that complete digestion of partially digested proteins and convert them to amino acids © 2016 by Elsevier Inc. All rights reserved. 43

Digestion (Cont. ) Fat digestion Ø Ø Bile contains no enzymes but emulsifies fats (breaks fat droplets into very small droplets) Pancreatic lipase changes emulsified fats to fatty acids and glycerol in small intestine © 2016 by Elsevier Inc. All rights reserved. 44

Absorption Mechanisms of absorption Ø Ø Nutrient absorption is process by which digested food moves from intestine into blood or lymph Foods and most water minerals and vitamins are absorbed from small intestine; some water and vitamin K also absorbed from large intestine © 2016 by Elsevier Inc. All rights reserved. 45

Absorption (Cont. ) Surface area and absorption Ø Ø Structural adaptations increase absorptive surface area Fractal geometry • Study of fragmented geometric irregular shapes, such as those in lining of intestine © 2016 by Elsevier Inc. All rights reserved. 46

Terms to Know Bolus: Ball of food moved involuntarily from the mouth to stomach Chyme: Food is mixed with gastric juices and broken down into semisolid form Jaundice: Yellowish skin discoloration caused by bile buildup Ulcer: Lesions that destroy stomach or intestine lining; can cause serious complications Diarrhea: Stools or fecal material become more fluid © 2016 by Elsevier Inc. All rights reserved. 47