The Digestive System

Digestive System Also known as the gastrointestinal (GI) tract or alimentary canal Long tube open at both ends Also has accessory organs Nutrients absorbed, waste eliminated Converts food into useable form

Mouth Salivary Glands Esophagus Liver Stomach Gallbladder Pancreas Small Intestine Large Intestine Appendix Anus

4 Steps to Nutrient Intake Ingestion Digestion - Prepares food for absorption - Mechanical and chemical breakdown of food Absorption - Small intestine Elimination

Two Types of Digestion Mechanical Chemical

Mechanical Digestion Physical breakdown of food Movement of food Mouth (chewing) and stomach (churning) Movement of food Peristalsis - wavelike involuntary muscle contractions

Chemical Digestion In mouth, stomach, small intestine Chemicals (e.g., HCl) and enzymes break down complex molecules e.g., Amylase in saliva - enzyme that breaks down starch (a carbohydrate)

Enzymes Break down substances Protein catalysts Specific to substrates

Oral Cavity (Mouth) Mechanical digestion (teeth) and chemical digestion (saliva with enzymes) Bolus of food forms and passes through pharynx into esophagus Epiglottis prevents food from entering trachea Bolus

Esophagus Muscular tube that connects pharynx to stomach Peristaltic contractions move food to stomach Cardiac sphincter at junction prevents food in stomach from going back into esophagus

Stomach J-shaped muscular organ to churn and squeeze Acts as a reservoir for food (1.5 L) Rugae (folds) allow for expansion Movement of food controlled by two sphincters: Cardiac sphincter: Between the stomach & the esophagus Pyloric sphincter: Between the stomach & the small intestine Cardiac sphincter

Stomach Digestion turns bolus into chyme – paste-like partially digested food Secretes HCl (pH of 2) Destroys microbes and breaks down food Primarily digests protein Pepsin, an enzyme only active at low pH

Small Intestine Major site of digestion and absorption 80% of nutrient absorption occurs here – diffusion About 6 m long, SMALLER diameter than large intestine, 3 sections Bile produced by liver breaks down fats Enzymes secreted by pancreas break down carbs, fats and proteins

Structure of Small Intestine Microvilli Villus Villi and microvilli - increase surface area, maximize absorption

Duodenum First section of small intestine Receives pancreatic secretions for further chemical digestion Basic pH Bile from gall bladder and bicarbonate ions from pancreas neutralize acidic chyme from stomach

Jejunum and Ileum Make up the other two sections of the small intestine. Where most nutrient absorption takes place. Peristaltic contractions continue to propel chyme through tract.

Large Intestine About 1.5 m long and has a LARGER diameter than the small intestine. Consists of four sections: Caecum Colon Rectum Anus.

Large Intestine Main function is to reabsorb water Bacteria produce vitamins which are absorbed Compacts unabsorbed material into feces Defecation: Rectal sphincter passes feces into rectum for temporary storage Anal sphincter passes feces from rectum out anus

Animated Digestion Video! Graphic Digestion Video!