Chapter 30.3: The Digestive System

Functions of the Digestive System Ingestion Take food into body Digestion Mechanical Physical breakdown of food into small pieces Chemical Enzymes break down food into individual nutrients Absorption Nutrients absorbed into body Elimination Waste is compacted and eliminated

The Mouth - Teeth Saliva Tongue Pharynx Incisors, cuspids, and bicuspids cut and tear food Molars grind food Saliva Amylase breaks down starch Tongue Forms a bolus, or ball of food Pushes food into back of throat, or pharynx Pharynx Contains epiglottis, which blocks the trachea and prevents choking

The Esophagus Connects the pharynx to the stomach Moves food by peristalsis Smooth, wave-like muscle contractions

The Stomach Is a muscular sac that continues mechanical and chemical digestion Chemical digestion Protein is broken down by the enzyme pepsin Hydrochloric acid (HCl) also breaks down food Mechanical digestion Stomach squeezes and churns food to produce chime Chyme is the mixture of food and digestive enzymes

The Small Intestine Begins at stomach and ends at large intestine First section called the duodenum Chemical digestion by enzymes continues after food is pushed from stomach Enzymes are made in the small intestine walls, or from the pancreas

The Small Intestine Absorption of nutrients into the blood occurs through villi Villi are fingerlike projections that line the small intestine, and are covered with microvilli Microvilli are tiny projections of cells on villi that aid nutrient absorption

The Pancreas Connects to the small intestine by a duct Makes and secretes sodium bicarbonate, which neutralizes stomach acid Makes and secretes enzymes, which break down food Also produces hormones that regulate blood sugar

The Liver and Gallbladder Liver produces bile Gallbladder stores bile, and secretes it by a duct into the small intestine Bile helps break down fats

The Large Intestine Also called the colon Connects to the small intestine and ends at the rectum Absorbs water from chyme Supports colonies of bacteria Compacts unused nutrients into solid waste

The Rectum and Anus Elimination occurs after the large intestine has compacted solid waste into feces Feces is stored in the rectum Anus is the muscle that controls release of feces