2 Digestive SystemAlso known as the gastrointestinal (GI) tract or alimentary canalLong tube open at both endsAlso has accessory organsNutrients absorbed, waste eliminatedConverts food into useable form
6 Mechanical Digestion Physical breakdown of food Movement of food Mouth (chewing) and stomach (churning)Movement of foodPeristalsis - wavelike involuntary muscle contractions
7 Chemical Digestion In mouth, stomach, small intestine Chemicals (e.g., HCl) and enzymes break down complex moleculese.g., Amylase in saliva - enzyme that breaks down starch (a carbohydrate)
8 EnzymesBreak down substancesProtein catalystsSpecific to substrates
9 Oral Cavity (Mouth)Mechanical digestion (teeth) and chemical digestion (saliva with enzymes)Bolus of food forms and passes through pharynx into esophagusEpiglottis prevents food from entering tracheaBolus
10 Esophagus Muscular tube that connects pharynx to stomach Peristaltic contractions move food to stomachCardiac sphincter at junction prevents food in stomach from going back into esophagus
11 Stomach J-shaped muscular organ to churn and squeeze Acts as a reservoir for food (1.5 L)Rugae (folds) allow for expansionMovement of food controlled by two sphincters:Cardiac sphincter: Between the stomach & the esophagusPyloric sphincter: Between the stomach & the small intestineCardiac sphincter
12 StomachDigestion turns bolus into chyme – paste-like partially digested foodSecretes HCl (pH of 2)Destroys microbes and breaks down foodPrimarily digests proteinPepsin, an enzyme only active at low pH
13 Small Intestine Major site of digestion and absorption 80% of nutrient absorption occurs here – diffusionAbout 6 m long, SMALLER diameter than large intestine, 3 sectionsBile produced by liver breaks down fatsEnzymes secreted by pancreas break down carbs,fats and proteins
14 Structure of Small Intestine MicrovilliVillusVilli and microvilli - increase surface area, maximize absorption
15 Duodenum First section of small intestine Receives pancreatic secretions for further chemical digestionBasic pHBile from gall bladder and bicarbonate ions from pancreas neutralize acidic chyme from stomach
16 Jejunum and IleumMake up the other two sections of the small intestine.Where most nutrient absorption takes place.Peristaltic contractions continue to propel chyme through tract.
17 Large IntestineAbout 1.5 m long and has a LARGER diameter than the small intestine.Consists of four sections:CaecumColonRectumAnus.
18 Large Intestine Main function is to reabsorb water Bacteria produce vitamins which are absorbedCompacts unabsorbed material into fecesDefecation:Rectal sphincter passes feces into rectum for temporary storageAnal sphincter passes feces from rectum out anus