1. The Digestive System

2. Two Divisions Alimentary Canal (or gastrointestinal (GI) tract)
Where food passes from mouth to anus
Organs: mouth, pharynx, esophagus, stomach, small intestine, large intestine
Accessory Digestive Organs
Contribute to digestion and absorption
Teeth, tongue, salivary glands, liver, gallbladder, pancreas

3. Layers of the GI Tract
Same four layers from esophagus to anus

4. Layers of the GI Tract Mucosa – innermost lining of tract
Secretion – mucus, enzymes, hormones
Protection – disease
Absorption – nutrients, ions, water, vitamins
Plica – folds that increase surface area

5. Layers of the GI Tract Submucosa – dense connective tissue
Binding – mucosa to muscularis
Contains blood vessels, lymph vessels, lymph nodes, nerves

6. Layers of the GI Tract Muscularis externa – smooth muscle
Contains circular and longitudinal fibers
Serosa - outermost layer
AKA visceral peritoneum

7. Functions of the Digestive System
Ingestion – “eating”
Propulsion – moving food through GI
Deglutition (swallowing) – voluntary
Peristalsis – wave-like contractions that move food – involuntary
Mass movements – large contractions in large intestine

8. Functions of the Digestive System
Mechanical digestion – food breakdown
chewing & mixing by tongue & teeth (mastication)
churning in the stomach
Segmentation – rhythmic contractions of small intestine that mixes food

9. Functions of the Digestive System
Chemical digestion – food breaks down into chemical building blocks
Uses enzymes
Mouth through small intestine
Hydrolysis reactions
Carbohydrates monosaccharides
Protein amino acids
DNA nucleotides

10. Functions of the Digestive System
Absorption - movement of digested end products from lumen of GI into blood or lymph
Defecation – elimination of wastes

11. The Mouth, Pharynx, & Esophagus
Salivary glands produce salivary amylase to start break down of complex carbohydrates.
Mastication – why?
Bolus formed in palate
Deglutition
Epiglottis protects trachea as food passes through pharynx
Peristalsis moves food through esophagus to stomach

12. The Stomach Cardioesophageal sphincter controls entrance
Rugae expand to accommodate food
Enteroendocrine cells produce the hormone gastrin to stimulate release of gastric juice
Parietal cells release hydrochloric acid to activate enzymes and kill bacteria
Mucous neck cells secrete mucus to protect the stomach wall from acid

13. The Stomach
Chief cells produce pepsinogen which is activated by acid to form pepsin (digests protein).
Processed food (chyme) enters the small intestine through the pyloric sphincter

14. The Small Intestine Three Parts:
Duodenum – 5% of length, but most activity is here, C-shaped
Jejunum – almost 40%, coiled
Ileum – almost 60%, coiled
Suspended from abdominal wall by mesenteries

15. Duodenum Trypsin produced by pancreas furthers protein digestion
Pancreatic amylase continues carbohydrate breakdown
Brush border enzymes of small intestine finish carb and protein digestion
Bile (produced by liver & stored in gall bladder) emulsifies fats for absorption
Pancreatic enzymes & bile production is controlled by hormones secretin and CCK, produced by small intestine when chyme is present

16. Jejunum & Ileum
Villi & microvilli (brush border) increase surface area of small intestine
Fat is absorbed by diffusion
Other molecules are absorbed through active transport

17. Large Intestine Remaining water is absorbed
Residue is further digested by resident bacteria, who produce vitamins (K & some B) and gas (more with carb- rich food)
Goblet cells produce mucus to ease passage of solid waste

18. Rectum & Anus
Mass movements push feces past internal anal sphincter (involuntary)
Relaxation of external anal sphincter is voluntary and results in defecation

19. Leptin & Ghrelin