THE PHYSIOLOGY OF THE DIGESTIVE SYSTEM

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

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

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

CHEMICAL TRANSFORMATIONS: Saliva secreted into mouth by salivary glands

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

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”

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

CHEMICAL TRANSFORMATIONS: Stomach releases gastric juices

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

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

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

LARGE INTESTINE MECHANICAL TRANSFORMATIONS: Churned to facilitate absorption of nutrients

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