Chapter 49 - Nutrients and the Digestive System I. Nutrients (chemical substances necessary for organisms to grow and function properly) 6 basic nutrients - 4 food groups (milk, meat, fruit and vegetable, grain) A. Carbohydrates 1. provide most of body s energy 2. Types a. monosaccharides - glucose, fructose, galactose (in fruit and honey) - directly absorbed b. disaccharides - sucrose (cane), lactose (milk), maltose (grains) - must be hydrolyzed into monosaccharides c. polysaccharides (complex carbo.) - starch (cereal grains, potatoes, beans, corn, rice) 1) cellulose - indigestible but provides fiber that stimulates smooth muscle contractions of digestive tract B. Proteins 1. compose body tissues, for growth, repair, enzymes, hormones etc. 2. made of amino acids a. 20 kinds b. nonessential (12) - body can make them c. essential (8) - must be obtained from food 3. complete proteins (contain the 8 essential) - meat, eggs, dairy products 4. incomplete proteins (don t contain all 8) - plant protein (Fig 49-2, p. 978) C. Lipids 1. concentrated energy source (2 times the energy/gram as carbo.) and build cell membranes
a. insulation, protective padding for organs 2. must be hydrolyzed to fatty acids and glycerol 3. Types a. saturated - single bonds between all carbons, max. H atoms (animal fat, butter, lard) b. unsaturated - at least one double bond - 2 or more (polyunsat) - plant oils except palm and coconut D. Vitamins (Table 49-1 p. 980) 1. serve as coenzymes 2. activate enzymes and help them function 3. needed in small quantities 4. Types a. fat soluble (A,D,E,K) - stored in fat tissue (accumulate) b. water soluble (B complex, C) - not stored, needed daily, excess excreted in urine 5. vitamin deficiency disorders E. Minerals (Table 49-2 p. 981) 1. required for normal functioning of body 2. needed in small amounts F. Water (Table 49-3 p. 982) 1. accounts for half of body weight 2. needed for chemical reactions 3. in plasma, tissue fluids, urine, sweat 4. helps regulate body temp. a. absorbs heat from cell reactions and distributes it b. perspiration evaporates from skin drawing heat away
II. Digestive System A. Digestion 1. breaking down food into molecules the body can use (occurs in gastrointestinal tract) a. mechanical (physical) - physically break down food into smaller pieces (increase surface area for enzymes to act) b. chemical - enzymes break down large molecules to small molecules that can be absorbed B. Mouth (1 minute or less) 1. mechanical - chewing a. incisors (sharp, flat) - cut food b. molars (broad, flat) - grind food 2. tongue keeps food on chewing surfaces 3. salivary glands a. parotid - cheek b. submaxillary - lower jaw c. sublingual - floor of mouth 4. saliva a. water b. mucus - softens and lubricates food c. salivary amylase - starch to maltose C. Pharynx 1. bolus - food ball 2. swallowing a. tongue up (hard palate) and back (soft palate - separates mouth and nasal cavity) b. food to pharynx c. epiglottis - flap preventing food from entering trachea d. food enters esophagus D. Esophagus (25 cm - 10 inches) (4-8 seconds)
1. muscular tube 25 cm long 2. connects pharynx with stomach 3. circular and longitudinal muscles alternate contractions - peristalsis (wave-like contraction forcing food down esophagus) 4. secretes mucus 5. no digestion here E. Stomach (3-4 hours) 1. muscular sac a. smooth muscle (circular, longitudinal, diagonal layers for twisting and turning) b. involved in mech. (churn contents) and chem. digestion 2. inner lining has mucus membrane of epithelial cells a. gastric pits - openings of gastric glands (some secrete mucus, some digestive enzymes, some HCl) 1) forms acidic gastric juice or fluid 3. inactive pepsinogen converted to enzyme pepsin at low ph a. pepsin - proteins to large polypeptides b. HCl also dissolves minerals and kills bacteria 4. mucus - protective coating to protect from HCl and pepsin (ulcer if it breaks down) 5. cardiac sphincter - circular muscle between esophagus and stomach a. lets food in and prevents reentry to esophagus 6. chyme - pastelike substance formed from churning and enzyme action 7. pyloric sphincter - valve controlling passage of chyme into small intestine
F. Small Intestine (21 ft.) (3-5 hours) 1. duodenum (25 cm - for digestion), jejunum, ileum 2. most chemical digestion and absorption here 3. when chyme enters, mucus secreted to protect from acid and enzymes 4. pancreas - accesory organ a. sodium bicarbonate - changes ph from acid to weak base b. pancreatic amylase - starch to maltose c. lipase - fats to fatty acids and glycerol d. trypsin - large polypeptides to small polypeptides 5. liver - accesory organ a. produces bile (stored in gall bladder) 1) released through common bile duct when chyme present b. bile emulsifies fats (breaks large fat globules into tiny droplets) c. increases surface area for enzyme attack 6. intestinal glands a. peptidase - small polypeptides to amino acids b. maltase - maltose to monosaccharides c. lactase - lactose to monosaccharides d. sucrase - sucrose to monosaccharides
7. absorption a. villi - finger-like projections that increase surface area (folds in lining also) 1) amino acids and monosaccharides diffuse into capillaries inside 2) fatty acids and glycerol enter lacteals to lymph vessels G. Large Intestine (colon) (5 ft.) 14-24 hours 1. ascending, transverse, descending, sigmoid, rectum 2. absorbs water, minerals, and vitamins 3. feces - solidified indigestible waste material(stored in rectum) 4. E. coli (bacteria) a. produce some amino acids and Vit. K 5. diarrhea - feces not in intestine long enough (little water absorbed) 6. constipation - feces in intestine too long (too much water absorbed) - not enough fiber in diet 7. appendix - at junction of small and large intestine (no known use)