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Chapter 15: Digestion & Nutrition I. Introduction to Digestion A. Digestion refers to the mechanical & chemical breakdown of foods so that nutrients can be absorbed by cells B. The digestive system includes: 1. 2. Pg. 413 alimentary canal (AC) – 9 meter long muscular tube from mouth to anus accessory organs – empty into the AC Pg. 412 C. Movements in the AC: mixing & propelling 1. Mixing occurs when smooth muscles contract rhythmically in small sections of the AC Pg 415 2. Propelling refers to peristalsis caused by contraction behind a mass of food as relaxation allows the mass to enter the next segment of the AC II. Organs of the Digestive System A. Mouth - first portion of AC; mechanical digestion by mastication (chewing) begins 1. Palate – forms roof of oral cavity: anterior hard palate – speech sounds, pushes food to pharynx posterior soft palate – with uvula, it closes off nasal cavity when swallowing Pg 415 2. Teeth a. 2 sets of teeth develop in sockets within the mandible & maxilla b. 20 primary teeth are shed in the order they appeared and are replaced by 32 secondary teeth Pg 416 c. d. Through the actions of chewing, teeth break food into smaller pieces, beginning mechanical digestion Teeth are adapted to handle food in different ways: incisors, cuspids, bicuspids, & molars Pg 417 Pg 417 e. Each tooth consists of a crown & a root, and is made of enamel, dentin, pulp, cementum, nerves, & blood vessels f. A tooth is held tight in its socket by a periodontal ligament 3. Pg 419 Salivary Glands a. these secrete saliva, which: moistens & dissolves food particles binds them together allows tasting helps to cleanse mouth & teeth begins carbohydrate digestion b. saliva contains enzyme amylase used to breakdown carbs, and mucous cells that produce lubricating and binding mucus c. Major Salivary Glands parotid glands secrete a clear, watery fluid rich in amylase submandibular glands & sublingual glands secrete a viscous (thick) fluid B. Pharynx 1. lies behind mouth 2. connects nasal & oral cavities with the larynx (breathing) and esophagus (food) Pg 416 C. Esophagus 1. muscular tube leading to stomach 2. produces mucus (moisture, lubrication) 3. lower esophageal sphincter prevents regurgitation of stomach contents D. Stomach: J-shaped muscular organ 1. mixes food with digestive juices (HCl) 2. propels food to small intestine 3. pyloric sphincter controls the release of food from stomach into small intestine 4. can only absorb small quantities of water and certain salts, alcohol, and some lipid-soluble drugs 5. Pg 420 4 regions: cardiac fundic body pyloric E. Pancreas 1. empties pancreatic juice into the small intestine through the pancreatic duct 2. pancreatic juice contains enzymes that digest carbohydrates, fats, proteins, and nucleic acids (DNA, RNA) Pg 424 F. Liver 1. 2. 3. 4. Pg 425 a large, reddish-brown organ, located in the upper right quadrant of the abdominal cavity metabolizes carbohydrates, lipids, & proteins filters blood, removing damaged red blood cells, foreign substances, toxins secretes bile, which performs lipid emulsification (lipids are broken down into smaller droplets to ↑ surface area for faster digestion) G. Pg 425 Gall 1. 2. 3. Bladder pear-shaped green sac under the liver stores bile for later release gall stones may form from: a. insufficient bile salts b. excessive cholesterol (stones) H. Pg 430 2. 3. 4. Small Intestine 1. 10 feet long with 3 parts: a. duodenum (10-12 in) b. jejunum (3 ft) c. ileum (6 ft) receives secretions from pancreas & liver completes digestion & absorption of nutrients using villi transports indigestible waste to the large intestine Pg 431 I. Large Intestine 1. 4 Parts: a. b. c. d. Pg 435 cecum – pouch colon – ascending transverse descending sigmoid rectum anal canal 2. Functions: a. NO digestion or absorption of nutrients, but it does secrete mucus b. Absorbs electrolytes (Na+, Cl-, K+) and water c. Contains bacteria that make vitamins and use cellulose (material from plant cell walls) d. forms & stores feces composed of undigested material, little water, few electrolytes, mucus, & bacteria both the color & odor of feces is due to the action of bacteria 3. Movements of the Large Intestine a. b. Peristalsis happens only 2-3 times per day Defecation is stimulated by a reflex that forces feces into the rectum where they can be expelled Pg 436 4. The anal canal opens to the outside as the anus & is guarded by 2 muscles: a. b. internal anal sphincter (involuntary) external anal sphincter (voluntary) NUTRITION I. Nutrition and Nutrients A. Nutrition is the study of nutrients & how the body utilizes them B. Nutrients are chemicals supplied from the environment that an organism requires for survival: 1. Carbohydrates Macro 2. Lipids Nutrients 3. Proteins 4. Vitamins Micro Nutrients 5. Minerals C. Carbohydrates, Proteins, & Lipids contain Calories 1. 1 calorie = the amount of energy needed to raise the temp of 1 gram of water by 1o Celsius 2. 1 Calorie = a kilocalorie used to measure food energy; 1000x greater than a calorie 3. Carbs & Proteins = 4 Calories/gram Lipids = 9 Calories/gram II. Carbohydrates A. Carbohydrates are used for sources of energy in the diet (125-175 grams/day to avoid protein breakdown) B. Forms: 1. starch from grains & some vegetables 2. glycogen from meat 3. disaccharides – sugars from cane sugar, beet sugar, & molasses 4. monosaccharides – sugars from honey & fruit 5. cellulose – found in plant cell walls bacteria can digest some, but most provides bulk (fiber), helping food move through the intestines C. Carbohydrate Utilization 1. Starches & Glycogen are broken down into monosaccharides: fructose, galactose, & glucose 2. Liver enzymes further convert fructose & galactose into glucose 3. Excess glucose is stored as glycogen in the liver & muscles (1st) fat in adipose tissue (2nd) 4. Neurons need a continuous supply of glucose to survive; if glucose is scarce, amino acids (from proteins) may be converted to glucose III. Lipids A. B. Lipids supply energy & make up membranes 1. 3 kinds: fats, phospholipids, cholesterol 2. No more than 30% of your daily calories should be lipids Dietary Lipids are triglycerides, found in plant- & animal-based foods 1. Saturated fats: animal origin (meat, eggs, milk, lard); palm & coconut oils; cholesterol 2. Unsaturated fats: plant origin (seeds, nuts, plant oils) Monounsaturated fats: olive, peanut, & canola oils are the healthiest IV. Proteins A. Proteins are polymers of amino acids & carry out important cellular functions: 1. enzymes control metabolism 2. hormones regulate processes 3. antibodies & clotting factors for blood 4. actin & myosin in muscle 5. keratin in skin & hair potential sources of energy too B. Adult cells can make 12 required amino acids 1. 8 can’t be = essential amino acids 2. All 20 must be present at the same time for proper growth & tissue repair 15 - 24 C. D. Protein Sources 1. Animal protein sources are complete proteins, b/c they contain all 8 essential amino acids 2. Plant protein sources are missing 1+ essential amino acids making them incomplete proteins Vegetarians should consume in combinations Daily Protein Requirements 1. 0.8 grams per kg body weight 2. Body weight in pounds ÷ 2 3. 60-150 grams Increase by 20-30g if pregnant or nursing V. Vitamins & Minerals – make reactions possible that extract energy from carbs, lipids, & proteins A. Vitamins are required in small amounts, and are not produced enough by cells water-soluble – B’s, C fat-soluble - A, D, E, K → B. Minerals are derived from the soil & essential in human metabolism (Ca, K, Fe, I, Cl etc.) VI. Adequate Diets A. An adequate diet providess sufficient energy (calories) & nutrients to support optimal growth and to maintain and repair body tissues B. Individual requirements for nutrients vary greatly with: age, sex, growth rate, physical activity, stress level, and genetic & environmental factors C. Malnutrition – poor nutrition 1. undernutrition: lack of food, poor quality food, inability to use nutrients 2. overnutrition: overeating or taking too many vitamin supplements 15 - 29 15 - 30