Digestion By analyzing the chemical formulas, you can determine that this molecule, CH3CH(NH2)COOH, is a(n) _____, whereas the molecule C5H10O5 is a(n) ________. • • • • A) cholesterol; amino acid B) amino acid; sugar C) nucleotide; glycerol D) fatty acid; sugar Announcements • Ch 15- Digestion • Digestive enzymes lab today (due next Wednesday, March 2) • Ch 15 online quiz due Friday, 11am • Bacteria lab- due Friday! • Quiz 4 Friday • Nutrition lab Friday Study Skills Workshop- 5 pts extra credit Wed. 2/23 - Ocean Campus, 4-4:30pm in S322 - Ocean Campus, 5:30-6pm in S334 - Mission Campus, 5:30-6pm in 364 Thursday 2/24 - Ocean Campus, 8:30-9am in S334 - Ocean Campus, 12-12:30 in S350 - Ocean Campus, 2-2:30pm in S307 Friday 2/25 - Ocean Campus, 2:30-3pm in S307 Saturday 2/26 - Ocean Campus, 10:00-10:30am in S350 Monday 2/28 - Ocean Campus, 10:30am-11am in S334 The Digestive System: An Overview True or false? • “You are what you eat.” • “If it’s true that you are what you eat, part of what is now my body used to be sitting in a box in the cereal aisle at Safeway.”-C. Phipps All living things are made of similar molecules • • • • • • • Carbohydrates Lipids Proteins Nucleic acids Also: Vitamins & Inorganic minerals All are digested and absorbed differently Metabolism- all the chemical reactions utilized by a living thing to power its activities Catabolism- breaking down food for energy Anabolism- building up molecules for structure How plants eat • Plants make their own food… • Using energy from the sun, • Electrons from water, • And CO2 from the atmosphere • Their food sources surround them How fungi eat • Fungi secrete digestive enzymes into their surroundings • They must absorb nutrients that they digest externally Animals can take it with them • Having a digestive system that is internal allows animals to be mobile • Generalized term is gut The simplest animals have an incomplete gut • Sponges (porifera) are filter feeders, and cnidarians (anemones and jellyfish) have an incomplete gut • Food enters, and waste is expelled, through same opening Your digestive system is on the “outside” of your body The digestive system absorbs nutrients from food • The digestive system (gastrointestinal tract or GI tract) is a 6-9 meter long tube • Food processing takes place to bring nutrients into the body • Food is transported through the lumen of the tube from the mouth to the anus The digestive tube has four layers • • • • Mucosa- epithelial layer Submucosaconnective tissue (blood vessels, etc.) Muscularis externa (2 smooth muscle layers, longitudinal and circular) Serosa- (protective connective tissue) Lumen- inner space Functions of the human digestive system • Mechanical breakdown and processing of food • Secretion- adding enzymes and surfactants to food to aid digestion • Digestion- chemical breakdown of food into absorbable particles • Absorption- uptake of food • Elimination- removing waste • Also: attenuation/interaction with gut flora • • • • • • • • Overview of the gastrointestinal (GI) tract Mouth Pharynx Esophagus Stomach Small intestine Gall bladder Liver Large intestine Overview of the gastrointestinal (GI) tract The mouth • Containment and mechanical processing are primary functions • Also, salivary amylase is secreted by salivary glands • Chewed food, mixed with saliva, is called a bolus Mouth flora influence rate of cavity formation of teeth • Streptococcus mutans is associated with greater rates of cavities • Food sugars are converted into acids • Is genetically modified yogurt the answer? Enzymes are a special kind of protein Enzymes are protein catalysts • Catalysts- things which speed up chemical reactions • Catalysts are not consumed in a reaction • -ase: The enzyme suffix Catalase How enzymes work Structure aids function An active site naturally fits substrate Enzyme specificity depends on shape Shape changes to fit substrateinduced fit Enzymes increase the rates of reactions by 108 or more Enzyme available with empty active site Enzymes are not consumed by the reactions they catalyze Active site Substrate (sucrose) Substrate binds to enzyme with induced fit Glucose Enzyme (sucrase) Fructose H2 O Products are released Substrate is converted to products Salivary amylases break down starch Amylases are secreted by the salivary glands of the mouth Sites where amylases cleave The Pharynx is the last point of voluntary control for digestion • Epiglottis covers breathing pathway to prevent choking • Once swallowing begins, it cannot be stopped The esophagus uses peristalsis to move food to stomach • Circular and longitudinal muscle layers cooperate to move bolus of food from pharynx to stomach Peristalsis • 2 layers of muscles work in coordination to move food • Circular muscles on outside layer • Long muscles on inside layer The stomach’s acidity kills most invaders • Hydrochloric acid pH=~2 • Peristaltic waves in the stomach also • Acid hydrolysis can digest carbohydrates, proteins • Food, now mixed with gastric juices, is now chyme Secretions of the stomach -Digestive enzymes: Pepsinogen pepsin, a proteinase -Cells of the stomach lining also secrete intrinsic factor, required for absorption of vitamin B12 Pyloric sphincter is controlled by hormones of duodenum Pepsinogen is a proenzyme • Stomach’s acid cleaves pepsinogen subunit, exposing active site of enzyme • Pepsin is a protease Helicobacter pylori is associated with stomach ulcers • Stress is also a cause, albeit much more frequent • Survives in stomach • Discovery earned Nobel prize for medicine, 2005 • Natural flora for some people • H. pylori not always so bad? The digestion of which class of foods begins in the mouth? 1. 2. 3. 4. 5. a. carbohydrates b. proteins c. lipids d. amino acids e. nucleic acids MAJOR ARTICLE: Helicobacter pylori Colonization Is Inversely Associated with Childhood Asthma • Yu Chen1,2,3 and Martin J. Blaser3,4,5 • Background.Asthma, a serious health problem worldwide, is becoming more common. Colonization with Helicobacter pylori, a major human indigenous (commensal) microbe, during early life may be relevant to the risk of childhood asthma. • Methods. We conducted cross‐sectional analyses, using data from 7412 participants in the National Health and Nutrition Examination Survey (NHANES) 1999–2000, to assess the association between H. pylori and childhood asthma. • Results.H. pylori seropositivity was inversely associated with onset of asthma before 5 years of age and current asthma in children aged 3–13 years. Among participants 3–19 years of age, the presence of H. pylori was inversely related to ever having had asthma (odds ratio [OR], 0.69; 95% confidence interval [CI], 0.45–1.06), and the inverse association with etc. Stomach chyme is sent through the pyloric sphincter to the duodenum • Chyme: food mixed with digestive juices • The small intestine has three regions: – Duodenum – Jejunum – Allium • Duodenum has digestive functions, as well as absorptive Gastric bypass surgery bypasses most of the stomach and duodenum • Patients feel much fuller, much more quickly • Regulation and nutrient uptake of duodenum bypassed • ~80% reduction in Type II diabetes • ~2% surgery-related mortality Alternatives to gastric bypass • Adjustable sleeves are less invasive than a bypass • Still really invasive • 30-day mortality of 0.11%, and 90-day mortality of 0.3% The pancreas contains two kinds of glands • Contains endocrine glands and exocrine glands • Exocrine glands: secrete proteolytic digestive enzymes into duodenum • Endocrine glands: secrete hormones (insulin, glucagon, etc.) into bloodstream to regulate blood sugar levels The liver has many functions • Bile is made in the liver-~1.5 liters/ day • Bile contains bile salts, which emulsify fats • Bile salts are made from cholesterol • Bile salts are stored in gall bladder Bile salts emulsify fats for absorption • Emulsifying- surrounding hydrophobic lipids with amphipathic molecule Other functions of the liver • • • • • Also synthesizes & releases cholesterol Synthesizes glucose & releases it Stores glycogen Process toxins (lead, mercury, pesticides, etc.) ~500 functions total Hepatitis, caused by one of many viruses, causes jaundice • Jaundice is caused by accumulation of bilirubin, a metabolic waste product from broken down heme Bilirubin is a metabolic waste product of broken-down heme Breakdown pathway of heme, and their associated colors A bruise showing multiple heme breakdown products Bile is stored in the gall bladder • When fats arrive in the duodenum, bile is released • When bile salts are insufficient to emulsify cholesterol, gallstones can form • Removal of the gall bladder is generally tolerated by the body The small intestine is designed to maximize surface area for absorption • Mucosal layer is folded • Folds have millions of villi • Villi themselves are made of absorptive cells with a brush border of microvilli submucosa serosa (thin connective tissue layer) thin layer of longitudinal muscle thick layer of circular muscle mucosa Extensive circular folds of mucosa Fig. 7.7a, p. 125 Villi (many fingerlike, epitheliumcovered projections from the mucosa) epithelium blood capillaries lymph vessel connective tissue vesicles artery vein lymph vessel Villi on one of the folds, longitudinal section One villus Fig. 7.7cd, p. 125 microvilli at free surface of absorptive cells ctyoplasm absorption mucus secretion (goblet cell) hormone secretion phagocytosis lysozyme secretion Fig. 7.7e, p. 125 The jejunum and illeum complete digestion in the small intestine • Chymosin and trypsin hydrolize proteins into amino acids • Lipases break down triglycerides into fatty acids and glycerol bile salts bile salts + + Micelles Fat Globules (triglycerides) Emulsification fatty acids, monoglycerides triglycerides + proteins © 2007 Thomson Higher Education Fig. 7.10, p. 129 The large intestine reclaims water and prepares feces for elimination • Active transport of salts leads to osmosis of water • This concentrates feces • Appendix is not used; can rupture, causing appendicitis • Feces is then passed to rectum for elimination Flora of large intestine secrete important vitamins • Vitamins B1, “K”vitamins (phylloquinones for blood coagulation) secreted • 10:1 ratio of human: bacterial cells in human body The breaking up of large units of fat into smaller ones is called 1. 2. 3. 4. 5. a. digestion. b. saponification. c. neutralization. d. emulsification. e. denaturation. Many nutrients are interconvertible Catabolism- breaking down food for energy Anabolism- building up molecules for structure Other nutrients cannot be replaced • Essential nutrients cannot be manufactured by the body • 8/20 Essential amino acids: Val, Thr, Phe, and Leu, Ile, Lys, Trp, and Met • Animal sources have complete protein • Vegetarian sources are often deficient in some amino acids but can be complemented • Beans have Ile and Lys but not Trp and Met. Corn has Trp, Met but not Ile and Lys.