1. The Digestive System: Mechanism for Nourishing the Body
Chapter 2
The Digestive System:
Mechanism for Nourishing the Body
2009 Cengage-Wadsworth

2. The Structures of the Digestive Tract & the Digestive Process
Main structures:
Oral cavity
Esophagus
Stomach
Small & large intestines
Accessory organs:
Pancreas
Liver
Gallbladder
2009 Cengage-Wadsworth

3. The Structures of the Digestive Tract & the Digestive Process
Lumen has 4 main layers:
Mucosa
Epithelium, lamina propria, muscularis mucosa
Submucosa
Connective tissue, lymphoid tissue, submucosal plexus
Muscularis externa
Circular & longitudinal smooth muscle, myenteric plexus
Serosa or adventitia
Connective tissue, visceral peritoneum
2009 Cengage-Wadsworth

4. The Oral Cavity Mouth & pharynx Salivary glands Enzymes in saliva
2009 Cengage-Wadsworth

5. The Esophagus Moves bolus from oral cavity to stomach Swallowing
Voluntary, pharyngeal, esophageal
Peristalsis
Gastroesophageal sphincter
Selected diseases & conditions of the esophagus - GERD
2009 Cengage-Wadsworth

6. The Stomach 4 main regions: Cardia region Fundus Body
Antrum or distal pyloric region
Grinds food & mixes with gastric juices to form chyme
Strong peristalsis for gastric emptying
2009 Cengage-Wadsworth

7. The Stomach Gastric glands: Cells in glands: Cardiac glands
Oxyntic glands
Pyloric glands
Cells in glands:
Neck (mucus) cells
Parietal (oxyntic) cells
Chief (peptic or zymogenic) cells
Enteroendocrine cells
2009 Cengage-Wadsworth

8. The Stomach Gastric juice HCl Enzymes - pepsin, amylase, lipase Mucus
Converts pepsinogen to pepsin
Denatures proteins
Releases nutrients from organic complexes
Acts as bacteriocide
Enzymes - pepsin, amylase, lipase
Mucus
Intrinsic factor
2009 Cengage-Wadsworth

9. The Stomach Regulation of gastric secretions
Hormones & peptides that inhibit gastric secretions
Hormones & neuropeptides that stimulate gastric secretions
Other factors
HCl release stimulated by gastrin, acetylcholine, histamine
2009 Cengage-Wadsworth

10. The Stomach
Selected diseases & conditions of the stomach - peptic ulcers
Regulation of gut motility & gastric emptying
2009 Cengage-Wadsworth

11. The Small Intestine Structural aspects of the small intestine
Folds of Kerckring - large circular folds of mucosa
Villi - finger-like projections
Microvilli - hair-like extensions of the cells’ plasma membranes
Brush border
Crypts of Lieberkühn
2009 Cengage-Wadsworth

12. The Small Intestine Regulation of intestinal secretions & motility
Immune system protection of the gastrointestinal tract
Mucosa-associated lymphoid tissue (MALT)
Gut-associated lymphoid tissue (GALT)
2009 Cengage-Wadsworth

13. The Accessory Organs The pancreas
Digestive enzymes produced by acinar exocrine cells
Pancreatic juice contains:
Bicarbonate
Electrolytes
Pancreatic digestive enzymes
Regulation of pancreatic secretions
2009 Cengage-Wadsworth

14. The Accessory Organs The liver Consists of lobes made of lobules
Portal circulation
Bile canaliculi
2009 Cengage-Wadsworth

15. The Accessory Organs The gallbladder Bile synthesis
Selected conditions/diseases of the gallbladder
Bile storage
The function of bile
The recirculation & excretion of bile
Bile circulation & hypercholesterolemia
2009 Cengage-Wadsworth

16. The Digestive & Absorptive Processes
Digestion
Breaking nutrients down
Occurs in lumen & at brush border
Most digestion & absorption occur in small intestine
Absorption may be by diffusion, facilitated diffusion, active transport, or pinocytosis/ endocytosis
2009 Cengage-Wadsworth

17. The Digestive & Absorptive Processes
Mechanism of absorption depends on:
Solubility (fat vs. water)
Concentration or electrical gradient
Size of molecule
Unabsorbed materials continue to colon
2009 Cengage-Wadsworth

18. The Colon or Large Intestine
Contracts to mix materials
Proximal colonic epithelia absorb Na, Cl, H2O
Materials dehydrated
Intestinal bacteria populations of interest
2009 Cengage-Wadsworth

19. Intestinal Bacteria (Microflora), Pre- and Probiotics, and Disease
Fermentation - breakdown of CHO & protein anaerobically
Generate lactate & short-chain fatty acids, gases
Probiotics - foods containing live bacterial cultures
Prebiotics - food ingredients that promote bacterial growth
2009 Cengage-Wadsworth

20. Intestinal Bacteria (Microflora), Pre- and Probiotics, and Disease
Probiotics are thought to:
Enhance immunity
Prevent colonization by pathogens
Lower pH of the colon
Transform/promote excretion of toxic substances
Enhance fecal bulk
2009 Cengage-Wadsworth

21. Coordination & Regulation of the Digestive Process
Neural regulation
Myenteric plexus - peristalsis, motility
Submucosal plexus - secretions, local blood flow
Regulatory peptides
Hormones
Paracrines
2009 Cengage-Wadsworth

22. Regulatory Peptides Gastrin Cholecystokinin (CCK) Secretin Motilin
Glucose-dependent insulinotropic peptide (GIP)
Peptide YY
Enteroglucagon
Amyline
2009 Cengage-Wadsworth

23. Regulatory Peptides Paracrine-acting substances Neurocrine peptides
Somatostatin
Glucagon-like peptides
Insulin-like growth factors
Neurocrine peptides
Vasoactive intestinal polypeptide (VIP)
Gastrin-releasing peptide (GRP)
Neurotensin
Substance powder (P)
2009 Cengage-Wadsworth

24. Perspective 2
An Overview of Selected Digestive System Disorders with Implications for Nourishing the Body
2009 Cengage-Wadsworth

25. Selected Disorders Disorder 1: Gastroesophageal reflux cisease
Disorder 2: Inflammatory bowel diseases
Disorder 3: Celiac disease
Disorder 4: Chronic pancreatitis
2009 Cengage-Wadsworth