3.5 The Digestive System Page

Stages of Digestion Ingestion-the taking in of nutrients. Digestion- the chemical and mechanical break- down of food into nutrients. Absorption-the taking up of digested molecules into the cells of the digestive tract. Egestion-the removal of waste food materials from the body.

Mouth Physical digestion-chewing

Teeth Incisors-cut food into smaller pieces. Bicuspids (premolars) and Canines pierce and tear. Molars crush and grind.

Mouth Chemical digestion Saliva -1 Litre per day -makes food wet (mucous, enzymes) -bolus salivary amylase starch  disaccharides

Swallowing Tongue pushes food back to throat Soft palate protects nasal openings Epiglottis protects airways

Peristalsis Waves of smooth muscle contractions stimulated by the presence of food.

Structure of the Stomach 2L capacity Site of protein digestion

Sphincters Circular muscle Like the drawstring of a bag Relaxed, food can move through Contracted, the opening closes

Stomach Layers: mucosa innermost layer, mucosa secretes digestive juices replaced every 3 days

Stomach layer: submucosa -middle layer -connective tissue with network of nerves and blood

Stomach layers: muscularis 3 muscle layers that contract and relax

Stomach layer: serosa Holds stomach in place and lubricates it

chyme food & gastric juice

Gastrin Hormone released when food is present in the stomach 2L of gastric juices released each day Enzymes digest the protein

Acid hydrochloric acid, pH Break down of fibrous foods kills germs Activates enzymes pepsinogen  pepsin nerves in walls of stomach stimulate churning

Absorption Water Medicine (aspirin) Alcohol

Mucous Protects the stomach lining from digestion by enzymes and acid

Stomach Ulcers Helicobacter pylori Neutralizes acid Burrows into mucous Dr. Robin Warren and Dr. Barry Marshall