1. THE PHYSIOLOGY OF THE DIGESTIVE SYSTEM

2. FOUR STAGES OF DIGESTION
Ingestion of food
Digestion of food
Absorption of food
Elimination of substances that have not been absorbed

3. DIGESTION FOOD TRANSFORMATIONS
1. MECHANICAL – nature of substance remains the same but physically changes (from larger to smaller)
2. CHEMICAL – bonds of the molecules are broken, giving rise to NEW substances

4. MOUTH MECHANICAL TRANSFORMATIONS: chewing (shredding, crushing)
Smaller pieces of food
Facilitates chemical digestion
Food mixed with saliva which makes it soft and moist
Food becomes BOLUS

5. CHEMICAL TRANSFORMATIONS:
Saliva secreted into mouth by salivary glands

6. PHARYNX MECHANICAL TRANSFORMATIONS:
Deglutition – action of swallowing food
Tongue pushes food back
Uvula rises closing nasal cavity
Epiglottis lowers blocking trachea
Bolus passes through pharynx and is pushed into esophagus

7. ESOPHAGUS MECHANICAL TRANSFORMATIONS:
Bolus moves through muscular contractions called peristalsis
Moves like this all the way to the anus
Like doing “the wave” or “the worm”

8. STOMACH MECHANICAL TRANSFORMATIONS:
Churning – movement resulting from muscular contractions on stomach wall
Soaks and mixes food with gastric juices
After a few hours in stomach, food becomes a liquid called chyme

9. CHEMICAL TRANSFORMATIONS:
Stomach releases gastric juices

10. SMALL INTESTINE
When food enters the S.I., three substances are secreted into it:
Intestinal juices (S.I.)
Bile (liver)
Pancreatic juices (pancreas)

11. MECHANICAL TRANSFORMATIONS:
Food is churned
Food advances through peristalsis (like in esophagus)

12. CHEMICAL TRANSFORMATIONS:
Walls of S.I. contain glands that secrete intestinal juices
Molecules are now absorbed by the body
Most absorption occurs here!
Absorbed by the villi of the intestinal walls

13. LARGE INTESTINE MECHANICAL TRANSFORMATIONS:
Churned to facilitate absorption of nutrients

14. ELIMINATION OF WASTE!!!!
Last activity taking place in the digestive tract
Last section of L.I. stores fecal matter which has not been absorbed
Fecal matter is mostly dietary fibre
Fats that have not been absorbed
LOTS OF BACTERIA = 40% OF FECAL MATTER!
Water too