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Summary for Chapter 3 – Digestion, Absorption, and Transport As Figure 3-1 shows, food enters the mouth and travels down the esophagus and through the upper and lower esophageal sphincters to the stomach, then through the pyloric sphincter to the small intestine, on through the ileocecal valve to the large intestine, past the appendix to the rectum, ending at the anus. The wavelike contractions of peristalsis and the periodic squeezing of segmentation keep things moving at a reasonable pace. Along the way, secretions from the salivary glands, stomach, pancreas, liver (via the gallbladder), and small intestine deliver fluids and digestive enzymes. Summary of Digestive Secretions and Their Major Actions Organ or Gland Target Organ Secretion Action Salivary glands Mouth Saliva Gastric glands Stomach Gastric juice Pancreas Small intestine Pancreatic juice Liver Gallbladder Intestinal glands Gallbladder Small intestine Small intestine Bile Bile Intestinal juice Fluid eases swallowing; salivary enzyme breaks down carbohydrate. Fluid mixes with bolus; hydrochloric acid uncoils proteins; enzymes break down proteins; mucus protects stomach cells. Bicarbonate neutralizes acidic gastric juices; pancreatic enzymes break down carbohydrates, fats, and proteins. Bile stored until needed. Bile emulsifies fat so enzymes can attack. Intestinal enzymes break down carbohydrate, fat, and protein fragments; mucus protects the intestinal wall. The many folds and villi of the small intestine dramatically increase its surface area, facilitating nutrient absorption. Nutrients pass through the cells of the villi and enter either the blood (if they are water soluble or small fat fragments) or the lymph (if they are fat soluble). Nutrients leaving the digestive system via the blood are routed directly to the liver before being transported to the body’s cells. Those leaving via the lymphatic system eventually enter the vascular system but bypass the liver at first. A diverse and abundant bacteria population support GI health. The regulation of GI processes depends on the coordinated efforts of the hormonal system and the nervous system; together, digestion and absorption transform foods into nutrients.