Digestion

Do Now Discuss the following with your seat partner: –Remember the last time you sat down to a dinner of your favorite foods? Recall everything that you did before you swallowed your first bite. Section Why do you cut up your food? 2. What role do your teeth play in eating? 3. Saliva is the fluid that is found in your mouth. What role do you think it plays in eating?

The Digestive System’s Function As food passes through the digestive system, it gets broken down distributing its nutrient value to the body The function of each organ of the digestive system is to help convert foods into simpler molecules that can be absorbed and used by the cells of the body

The Digestive System Structures The digestive system includes: –Mouth –Pharynx –Esophagus –Stomach –Small intestine –Large intestine Major accessory structures that add secretions to the digestive system include: –Salivary glands –Pancreas –Liver

Mouth Salivary glands Stomach Pancreas (behind stomach) Large intestine Small intestine Rectum Gallbladder (behind liver) Liver Esophagus Pharynx Figure 38–10 The Digestive System

Mouth & Salivary Glands Teeth –Protected by enamel –Chewing begins the process of mechanical digestion = physical (mechanical) breakdown of large pieces of food into smaller pieces (cutting, tearing, crushing) Saliva –Secreted by salivary glands –Moisten food making it easier to chew –Begins the process of chemical digestion = Amylase (digestive enzyme) chemically breakdown large starch molecules into smaller sugar molecules –Lysozyme enzyme fights infection

Pharynx Remember from the Respiratory System: The pharynx (throat) is a tube in the back of the mouth that passes both air and food Epiglottis (flap of tissue) covers the trachea to ensure food continue to move along digestive tract

Esophagus Food tube Bolus (chewed clump of food) moves along by contractions of smooth muscle surrounding the esophagus = peristalsis Cardiac sphincter closes esophagus after food has passed into the stomach preventing stomach contents from moving back into the esophagus (heart burn occurs when stomach acid splashing into the esophagus)

Stomach A large muscular sac made of smooth muscle that mechanically and chemically digests food Chemical digestion occurs as gastric glands in the stomach lining secrete mucus to protect the inner wall while pepsin and hydrochloric acid break down protein –Ulcers = a hole in the stomach wall caused by a bacterial infection that eats away at the lining of the stomach Mechanical digestions occurs as the stomach muscles contract to churn and mix stomach fluids producing a mixture = chyme –Pyloric valve opens allowing chyme to flow from the stomach into the small intestine

Duodenum More chemical digestion of chyme occurs in the duodenum (the first part of the small intestines) Chyme mixes with enzymes and digestive fluids from the pancreas and the liver (accessory structures)

Pancreas A gland that produces hormones that regulate blood sugar levels Produces enzymes that break down carbohydrates, proteins, lipids, and nucleic acids Produces sodium bicarbonates (a base) that neutralizes stomach acid

Liver Produces bile = “detergent” dissolving fat droplets Bile is stored in the gallbladder

Liver Gallbladder Duodenum Bile duct Pancreas Pancreatic duct To small intestine Figure 38–13 The Liver and the Pancreas Section 38-2

Small Intestine Made of three parts: duodenum, jejunum, and ileum Where chemical digestion is completed The folded surfaces are covered with villi = small fingerlike projections that increase the surface area of the small intestines for greater absorption of nutrients The products of carbohydrate or protein digestion are absorbed into capillaries in the villi and microvilli Undigested fats are absorbed by lymph vessels = lacteals

Small Intestine Villus Circular folds Villi Epithelial cells Capillaries Lacteal Vein Artery Figure 38–14 The Small Intestine Section 38-2

The Digestive Enzymes Site Mouth Stomach Small intestine (from pancreas) Small intestine Site Mouth Stomach Small intestine (from pancreas) Small intestine Enzyme Role in Digestion Section 38-2 Salivary amylase Pepsin Amylase Trypsin Lipase Maltase, sucrase, lactase Peptidase Breaks down starches into disaccharides Breaks down proteins into large peptides Continues the breakdown of starch Continues the breakdown of protein Breaks down fat Breaks down remaining disaccharides into monosaccharides Breaks down dipeptides into amino acids.

Large Intestine Food entering large intestine is basically nutrient-free, mainly made of water, cellulose (fiber), and other indigestible substances Removes water left in the chyme by absorbing it across the large intestine wall –If water removal is inefficient, diarrhea occurs and can be dangerous due to the loss of salts and water Intestinal bacteria help with digestion –The appendix is believed to have formerly stored bacteria to assist with cellulose digestion Solid concentrated waste (feces) is excreted through the rectum

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Ulcer reading Discuss the reading