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Nutrition and Digestion Vitamin A and Learning In The News Nutrients • Raw materials – Growth – Repair – Maintenance – Reproduction • Energy Classes of Nutrients • • • • • • Carbohydrates Lipids Proteins Minerals Vitamins Water Macronutrients • Carbon-containing compounds • Energy and raw material • Includes carbohydrates, lipids, & proteins • Body needs substantial amounts Carbohydrates • Should supply 45-65% of daily energy • Includes fruits, vegetables, whole grains • more low glycemic than high glycemic Proteins • Should supply 10-35% of daily energy • Proteins made of 20 amino acids • Essential amino acids must come from diet Fats • Should supply 20-35% of daily energy • Types of fats – Monosaturated (good) – Polyunsaturated (good) – Saturated (bad) – Trans fats (bad) Vitamins • • • • • • Play vital role in body function Most are derived from diet Required in small amounts Excess of some can be toxic fat soluble: vitamins A,D,E,and K water soluble: the other nine vitamins Minerals • Inorganic substances • Transported as ions by bloodstream • Variety of uses Water • No set amount daily • Body must maintain normal hydration Digestion • Breaking of food particles into molecules • Unnecessary in autotrophs, (self feeders) • Two types of digestion – Intracellular – Extracellular Organisms with Intracellular Digestion Organisms with Intracellular & Extracellular Digestion Extracellular Digestion Fungi Extracellular Digestion Most Animals Extracellular Digestion • In organisms with & without a digestive system – Fungi – no digestive system – Most animals – digestive system • Relies on enzymes (chemical digestion) • Mechanical digestion may also be present Human Digestion • Mechanical Digestion – Oral cavity by teeth – Stomach churning • Chemical digestion – Hydrochloric acid-denatures proteins, softens connective tissue, converts pepsinogen to pepsin & kills most bacteria – Bile salts emulsify lipids – Enzymes cleave chemical bonds (see table 27.3) • proteases, amylases, lipases Digestion in the Mouth • Salivary glands – Produces saliva • Mostly water • Some enzymes – Salivary amylase • Starch breakdown – Bacteria killing enzymes – mucus Digestion in the Mouth • Teeth – Mechanical digestion – Different teeth • Different functions • Fit omnivore diet Swallowing • Food is formed into a bolus – Chewed & moistened – Formed by tongue • Bolus is pushed into upper pharynx • Soft palate seals off nasopharynx Epiglottis • Folds over opening to larynx • Directs food into esophagus • Esophagus moves food toward stomach – Peristalsis = slow rhythmic squeezing – Gravity helps movement Peristalsis Stomach • Muscular sac – Churns & mixes food • Gastric glands – Produce gastric juice • Pepsinogen to pepsin • hydrochloric acid – Gastrin • Hormone • Controls gastric juices – Hydrochloric acid – Mucus-protection Structure of Stomach Food in the Stomach • Mixed with gastric juices (hydrochloric acid & pepsinogen) • Churned by muscles (3 layers of smooth muscles) • Leaves as paste (chyme) • Process takes 2-6 hours Small Intestine • Site of most digestion • Site of nutrient absorption • Area of association with accessory organs – Liver – Pancreas – Gall bladder Pancreas • Secretes many enzymes (proteases, amylase, lipase) • Empties into duodenum • Alkaline solution to help neutralize acids (sodium bicarbonate) Liver • Secretes bile (stored in gall bladder) • Components: Bile salts & bile pigments • Emulsifies fats Gall Bladder • Stores bile • Releases bile into duodenum Digestion in Small Intestine • Pancreatic amylase – Carbohydrates to maltose • Pancreatic proteases – Chymotrypsin – Trypsin – Carboxypeptidase • Pancreatic lipase – Fats • Disaccharidases (sm. Int.) – Further breaks down sugars • Peptidases (sm. intestine) Absorption in Small Intestine • Villi & microvilli Projections to increase surface area • Infoldings – increase surface area • Energy helps nutrients cross membranes • Nutrients diffuse into capillaries – Blood capillaries for all but lipids – Lacteals pick up lipids Hormones Control Digestive Enzymes Large Intestine • Areas of Colon – Cecum – Rectum – Terminates at anus Large Intestine Function • Concentration & elimination of solids • No digestive function • Absorption of water & sodium ions • Home for bacteria that produce vitamin K Overweight & Obesity • Risk factors for many medical conditions End chapter 27
