1. Digestive System
Chapter 23

2. Overview

3. Digestive Processes

4. Functional Concepts Mechanical and Chemical Stimuli
Intrinsic and extrinsic Controls
Two types of reflexes
Short =enteric (local)
Long =CNS and autonomic nerves

5. Digestive Anatomy Overview
Hepatic portal system
4 layers
Mucosa -mucous membrane
Submucosa -areolar tissue with blood and lymphatic vessels
Muscularis Externa -circular and longitudinal muscle layers
Serosa -areolar and simple squamous
Enteric Nervous System
Submucosal plexus
Myenteric plexus

6. Functional Anatomy

7. Functional Anatomy

8. Saliva Greater than 97% water PH 6.75-7.0 Electrolytes
Enzymes: Salivary amylase and lingual lipase
Mucin -glycoprotein
Immune proteins: Lysozyme, definsin, IgA
Urea and Uric acid
Naturally occurring bacteria ml

9. Salivary Control Intrinsic salivary glands keep mouth moist
Extrinsic glands moisten food
Food entering mouth activates
Parasympathetic innervation triggers enzyme rich saliva
Sympathetic triggers thick saliva (mucin rich)
Chemical and mechanical stimulate nuclei in pons and medulla
Sight and smell of food also activate
Lower GI irritation, spicy food, acidic food increase saliva production

10. Teeth and Gums Mechanical breakdown of food Oral disease may cause:
Atherosclerotic plaques
Clotting within coronary and cerebral arteries

11. Pharynx and Esophagus
Pharynx contains friction free stratified squamous epithelia
Esophagus is a muscular tube
GERD
Hiatal hernia

12. Digestive Process: Mouth to Esophagus
Mechanical breakdown
Deglutition (swallowing) uses 22 muscle groups
Buccal phase -voluntary movement within mouth
Pharyngeal-esophageal phase -involuntary movement controlled by pons and medulla

13. The Stomach

14. Stomach Simple columnar epithelium -secretes thick alkaline mucous
Gastric pits and glands
Secretions depend upon location
Mucous neck cells -thin mucous
Parietal cells -secretes H+, Cl-, intrisic factor
Chief cells -pepsinogen and lipases
Enteroendocrine cells -histamine, serotonin, somatostatin, gastrin

15. Homeostatic Imbalances
Gastric Ulcers
90% caused by Helicobacter pylori
10-20% of infected show symptoms
Inhibit or lessen HCl production
Damage stomach epithelium
Disrupt cell junctions
Promote chronic inflammation

16. Digestive Processes in the Stomach
Protein digestion begins
Alcohol and aspirin absorb into blood stream
Secretion of intrinsic factor
Required for absorbtion of vitamin B12
B12 is needed for RBC production

17. Regulation of Gastric Secretion
Neural mechanisms
Hormonal mechanism
Stimuli act on brain, stomach, intestine
Three phases: cephalic, gastric, intestinal
Not mutually exclusive phases

18. Cephalic (Reflex) Phase
Short, lasting only minutes
Prepares stomach to receive food
Sight and smell of food are the trigger
Stimulates mucous, chief, parietal and G cells
Conditional response
Special senses → hypothalamus → medulla → vagus → enteric plexus → stomach glands

19. Gastric Phase 3-4 hours Neural and hormonal response Triggers
Distension of stomach
Increase in pH (decrease in acidity)
Presence of undigested materials (proteins)

20. Gastric Phase Neural response Produces mixing waves
Stretch and chemoreceptors trigger short (myenteric) reflexes
Ach from parsympathetic neurons stimulates parietal and chief cells
Increase in HCl and Pepsinogen
Proteins, alcohol, caffine stimulate chemoreceptors

21. Gastric Phase Hormonal response Alkaline tide
Increasing gastrin levels stimulates parietal and chief cells
Gastrin enters blood stream circulates back to stomach
Increase in HCl and Pepsinogen
Decrease in pH (acidity)
Increase in gastric motility
Alkaline tide

22. Intestinal Phase Very long, lasting hours Controls gastric emptying
Neural and hormonal responses
Neural Responses
Chyme leaving stomach relieves distension
No-longer stimulating stretch receptors
Distension of duodenum by chyme stimulates intestinal stretch receptors =enterogastric reflex
Inhibits medulla (gastrin secretions) and local reflexes (gastric contractions)
Stimulates contraction of pyloric sphincter
Mucous production stimulated in duodenum to protect intestine

23. Intestinal Phase Hormonal response
Triggered by the arrival of chyme in duodenum
Arrival of lipids and carbohydrates
Stimulates cholesystokinin (CCK) and gastric inhibitory peptide (GIP)
CCK inhibits gastric secretion of acids and enzymes
GIP inhibits gastric secretion and rate of contraction
Meals low in fat enter intestine quicker than those high in fat
Allows more time for lipids to be broken down by intestine
Decrease in ph stimulates enteroendocrine cells to release secretin
Secretin inhibits parietal and chief cells
Stimulates pancreas to produce bicarbonate
Stimulates liver to secrete bile
Partially digested proteins in duodenum stimulate G cells in duodenal wall.
G cells produce gastrin which circulates back to stomach increasing acid production
Gastric processing meets digestive requirements of specific meals

25. Gastric Motility and Emptying
Response to distension of stomach
Gastric Contractile Activity
Smooth muscle pacemaker cells
Interstitial cells of Cajal set basic electrical rhythm (BER)
Set maximum rate of contraction
Do not initiate contractions
Regulation of Gastric Emptying
Stomach and duodenum work in conjunction