1. Advanced Biology
The Digestive System

2. Overview of Digestive System
Alimentary canal (gastrointestinal – GI – Tract) is the continuous, muscular digestive tube that winds through the body
Digest = dissolve
Absorbs digested fragments through its lining into the blood

3. Digestive Process 1. Ingestion – taking in food through mouth
2. Propulsion – swallowing or the process of moving food through the Alimentary canal
Peristalsis – alternate waves of contraction and relaxation of muscles in the organ walls
3. Mechanical digestion – physically prepares food for chemical digestion by enzymes
Segmentation – rhythmic local constrictions of the intestine

4. Digestive Process
4. Chemical Digestion – a series of catabolic steps in which complex food molecules are broken down to their monomers
5. Absorption – the passage of digested end products from the lumen of the GI tract to the blood
6. Defecation – elimination of indigestible substances from the body

5. Alimentary Canal Mouth Pharynx Ingestion of food Propulsion
Mechanical digestion – chewing (mastication)
Chemical digestion - starches
Pharynx

6. Alimentary Canal Esophagus Stomach Propulsion
Mechanical digestion and propulsion
Chemical digestion (proteins begun by pepsin); gastric juices
Absorption – fat-soluble substances (aspirin, alcohol, some drugs)

7. Stomach

8. Alimentary Canal Small intestine Mechanical digestion and propulsion
Continually mixes contents with gastric juices
Chemical digestion – digestive enzymes from pancreas
Border enzymes attached to villi – digestion of all foods
Absorption – breakdown of carbohydrate, protein, fat, nucleic acid, vitamins, electrolytes, and water

9. Small Intestine Four layers of small intestine: The mucosa Submucosa
Muscularis externa
serosa

10. Small Intestine

11. Alimentary Canal
Large intestine (leads to the terminal opening – anus) “the water-wringer”
Chemical digestion – remaining food residues are digested by bacteria (produce vitamin K and some B vitamins)
Absorption – absorbs almost all remaining water, electrolytes (especially NaCl) and vitamins produced by bacteria
Propulsion – propels feces toward rectum
Defecation

12. Alimentary Canal Human cadaver GI tract is about 30ft (9m) long
Shorter in living humans because of muscle contraction
Food is outside of the body because the canal is open to the environment

13. Accessory Digestive Organs
Teeth – grinding, tearing, etc.
Tongue – taste, swallowing, movement, etc.
Gallbladder – store bile (digestive enzyme) from liver
Digestive glands:
Salivary glands – produce saliva (digests starches)
Liver – produce bile
Pancreas – produce and secrete other digestive enzymes

14. Functional Concepts
1. Digestive activity is provoked by a range of mechanical and chemical stimuli
2. Controls of digestive activity are both extrinsic (CNS) and intrinsic (“In- house”)