Digestive System Functions Ch 14

Digestive System Major Functions Digestion of food Absorption of nutrients

6 major activities 1.Ingestion – Food placed in mouth 2.Propulsion – Food is moved from one organ to the next Peristalsis- smooth muscle pushes food through digestive tract 3.Mechanical digestion – Mixing food in mouth and stomach 4.Chemical digestion – Breaking down of large food molecules by enzymes 5.Absorption – Digested product absorbed in blood 6.Defecation – Elimination of indigestible substances in the form of feces

Mouth Ingestion Mechanical digestion – Teeth and tongue Chemical digestion – Saliva Amylase breaks down starches Food propulsion- 1 st phase: buccal phase (voluntary) – Bolus (food mass) forced into pharynx by tongue No absorption occurs

Pharynx and Esophagus Passageways to the stomach Food propulsion – Peristalsis – 2 nd phase Pharyngeal-esophageal phase (involuntary) – Soft palate closes off nasal cavity – Tongue blocks off mouth

Stomach Food opens cardioesophageal sphincter and enters stomach Food breakdown – Hormone gastrin stimulates production of gastric juices HCl, protein digesting enzymes (pepsinogen) and mucus – Mechanical digestion – Produces chyme

Stomach continued… Food propulsion – Peristalsis in lower half of stomach pushes small amounts of chyme into small intestines Little to no absorption

Small Intestines Food breakdown and absorption – Chemical digestion Sugars are broken down into simple sugars Pancreatic juice breaks down starch, proteins, fats (lipase) and nucleic acids Bile from gall bladder and liver emulsifies fats Chyme is neutralized Food propulsion- peristalsis

Large Intestines Food Breakdown and absorption – Bacteria metabolize some of the remaining nutrients make vitamins K and B Absorption of only the vitamins and water Propulsion of feces – Peristalsis and mass movements (slow, powerful contractions) that move feces toward rectum