Digestion, Absorption, and Transportation Unit #3

Learning Targets I can identify the nutrients in foods and their main functions. I can describe the digestive process and its stages. I can summarize the body’s absorption of nutrients. I can describe how the body uses nutrients both now and later. I can explain Basal Metabolic Rate and how it relates to calories.

Digestion Vocabulary Digestion: Gastrointestinal Tract: The process by which food is broken down into absorbable units. Gastrointestinal Tract: The digestive tract. Digestive System: All the organs and glands associated with the ingestion and digestion of food. Bolus: A portion; with respect to food, the amount swallowed at one time. Chyme: The semiliquid mass of partly digested food expelled by the stomach into the duodenum. Peristalsis: Wavelike muscular contractions of the GI tract that push its content along. Segmentation: A periodic squeezing and partitioning of the intestine at intervals along its length by its circular muscles.

Digestion 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 gall bladder), and small intestine deliver fluids and digestive enzymes.

“The Gastrointestinal Tract” In-Class Activity

Summary of Digestive Secretions and Their Actions Organ or Gland Target Organ Secretion Action Salivary Glands Mouth Saliva Fluid eases swallowing; salivary enzyme breaks down carbohydrate. Gastric Glands Stomach Gastric Juice Fluid mixes with bolus; hydrochloric acid uncoils proteins; enzymes break down proteins; mucus protects stomach cells. Pancreas Small Intestine Pancreatic Juice Bicarbonate neutralizes acidic gastric juices; pancreatic enzymes break down carbohydrates, fats, and proteins. Liver Gallbladder Bile Bile stored until needed. Bile emulsifies fat so enzymes can attack. Intestinal Glands Intestinal Juice Intestinal enzymes break down carbohydrate, fat, and protein fragments; mucus protects the intestinal wall.

Absorption The many folds and villi of the small intestine dramatically increase its surface area, facilitating nutrient absorption. Villi: Fingerlike projections from the folds of the small intestine. Absorption: The uptake of nutrients by the cells of the small intestine for transportation into either the blood or the lymph. 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). Lymph: A clear yellowish fluid that is almost identical to blood except that it contains no red blood cells or platelets.

The Circulatory System 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. Lymphatic System: A loosely organized system of vessels and ducts that convey fluids toward the heart.

Regulation of Digestion and Absorption Digestion and absorption depend on the coordinated efforts of the hormonal system and the nervous system. Together, they regulate the processes of transforming foods into nutrients.

Bibliography Rolfes, S.R. & Whitney, E. (2005). “Understanding nutrition.” Thomson Wadsworth; Belmont, California.