38–2 The Process of Digestion Photo Credit: © Fred Hossler/Visuals Unlimited Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Mouth The function of the digestive system is to help convert foods into simpler molecules that can be absorbed and used by the cells of the body. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Digestion The digestive system includes the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum & anus. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Digestion Other structures add secretions to the digestive system, and aid in digestion. They are called accessory organs. These include the salivary glands, pancreas, and liver. Food does not actually pass through them. Copyright Pearson Prentice Hall

38–2 The Process of Digestion The Digestive System Mouth Pharynx Salivary glands Esophagus Liver Stomach The digestive system includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. Because the pancreas and most of the gallbladder are behind other organs, their locations are indicated by dotted lines. Pancreas Gallbladder Large intestine Small intestine Rectum Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Mouth The Mouth Chewing begins mechanical digestion, which is the physical breakdown of large pieces of food into smaller pieces. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Mouth The teeth cut and grind the food and the salivary glands secrete saliva, which moistens food and makes it easier to chew. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Mouth Saliva helps ease the passage of food through the digestive system and also begins the process of chemical digestion. Chemical digestion = chemically changing the food / breaking it down into its building blocks (ex. protein amino acids) Saliva contains an enzyme called salivary amylase that breaks the chemical bonds in starches and releases sugars. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Pharynx Food is swallowed into the pharynx The epiglottis blocks the trachea so food doesn’t go “down the wrong pipe” Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Esophagus The Esophagus From the pharynx, the chewed food, or bolus, passes through the esophagus into the stomach. Food is moved along by contractions of smooth muscle (peristalsis) which squeeze the food through the esophagus into the stomach. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Esophagus Esophagus Bolus Peristalsis Muscles contracted Stomach Muscles in the walls of the esophagus contract in waves. Each wave pushes the chewed clump of food, or bolus, in front of it. Eventually, the bolus is pushed into the stomach. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Stomach The Stomach Food from the esophagus empties into the stomach. The stomach continues mechanical and chemical digestion. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The stomach - It is separated from the esophagus by the cardiac sphincter The stomach wall secretes gastric juices, pepsin (a hormone) and HCl. a thick lining of mucus protects the walls of the stomach from the acidic gastric juices Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Functions of the stomach: Storage – many folds, can hold 2-4 liters Mixing – food + gastric juices = chyme Physical digestion – grinds food into smaller pieces, HCl kills pathogens Chemical digestion – pepsin catalyses the breakdown of proteins into large peptides Controlled release – chyme leaves via the pyloric sphincter Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Small Intestine The Small Intestine Most chemical digestion and absorption of food occurs in the small intestine. Copyright Pearson Prentice Hall

Absorption in the Small Intestine The folded surfaces of the small intestine are covered with fingerlike projections called villi. Villi are covered with microvilli which provides an enormous surface area for the absorption of nutrient molecules. Copyright Pearson Prentice Hall

Absorption in the Small Intestine Villus Small intestine Circular folds Epithelial cells Villi Capillaries Lymph vessel The lining of the small intestine consists of folds that are covered with tiny projections called villi. Within each villus there is a network of blood capillaries and lymph vessels that absorb and carry away nutrients.  Vein Artery Copyright Pearson Prentice Hall

Absorption in the Small Intestine actions of the small intestine: - food continues to be digested chemically - bile is released from gallbladder to emulsify fat (break fat into smaller droplets) here - enzymes are secreted from the pancreas to digest starch, proteins, & lipids here - nutrient absorption –now that the macromolecules are smaller, they are absorbed into the bloodstream Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Small Intestine Accessory Structures of Digestion Liver Bile duct Pancreas Gallbladder Pancreatic duct Duodenum Accessory structures, including the liver and pancreas, add secretions to the digestive system. The pancreas secretes enzymes that help break down carbohydrates, proteins, and fats. To rest of small intestine Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Small Intestine Accessory Structures of Digestion Just behind the stomach is the pancreas. During digestion, the pancreas produces digestive enzymes and it produces a base that neutralizes stomach acid so that these enzymes can be effective. It also produces blood sugar regulating hormones like insulin. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Small Intestine Assisting the pancreas is the liver, which produces bile. Bile emulsifies fat into smaller droplets. Bile is stored in the gallbladder. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Large Intestine The Large Intestine When chyme leaves the small intestine, it enters the large intestine, or colon. The large intestine removes water from the chyme. It also absorbs vitamin K & B formed by bacteria in a symbiotic relationship with us Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Water is absorbed quickly, leaving undigested materials behind & forming feces. Concentrated waste material passes through the rectum and is eliminated via the anus. Copyright Pearson Prentice Hall

Digestive System Disorders Stomach acids sometimes damage the organ’s own lining, producing a hole in the stomach wall known as a peptic ulcer. Most peptic ulcers are caused by the bacterium H. pylori. Other digestive disorders include diarrhea and constipation. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–2 Food is moved through the esophagus into the stomach by air pressure. muscle contractions. gravity. swallowing. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–2 The enzyme in saliva that begins the digestion of starch is amylase. pepsin. lysozyme. peptidase. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–2 Stomach muscles contract to churn and mix stomach fluids and food, producing a mixture known as chyme. amylase. bile. acid. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–2 Absorption of vitamins, minerals, and digested food molecules takes place in the stomach. small intestine. large intestine. duodenum. Copyright Pearson Prentice Hall