Chapter 4 Carbohydrates Sugars Starches Fibers 11 7 12 4 57 PM Simple Carbohydrates Monosaccharides single sugars Disaccharides sugars composed of pairs of monosaccharides Polysaccharides large molecules composed of chains of Complex Carbohydrates monosaccharides What is a carbohydrate Compounds composed of carbon oxygen and hydrogen arranged as monosaccharides ext Molecular formula CH2O Written in nutrition CHO Chemical Bonds with other atoms Carbon atoms can form 4 bonds Nitrogen atoms can form 3 bonds Oxygen atoms can form 2 bonds Hydrogen atoms can form 1 bond Most of the monosaccharides important in nutrition are Hexoses Hexoses are simple sugars with six atoms of carbon and the formula is C6 H12 O6 3 Important Monosaccharides in Nutrition 1 Glucose also known as dextrose commonly called blood sugar serves as an essential energy source for all the boys activites Glucose is one of the two sugars in every disaccharide and the unit from which polysaccharides are made 2 Fructose the sweetest of the sugars has the same chemical formula as glucose C6 H12 O6 but differs in structure Fructose is naturally occurring in fruits and honey 3 Galactose occurs naturally as a single sugar in a few foods same chemical formula however differs in structure Disaccharides are pairs of three monosaccharides each containing glucose and the second member of the pair is either fructose galactose or another glucose 1 Maltose consists of 2 glucose units maltose is produces whenever starch breaks down which happens in human digestion during the breakdown of carbohydrates maltose is sometimes known as a malt 2 Sucrose fructose glucose sucrose sucrose is made into table sugar by being refined from sugarcane and sugar beets then sugar granulated 3 Lactose glucose galactose lactose commonly known as milk sugar lactose contributes half of the energy Kcals in fat free milk Chemical Reactions Condensation Reaction a chemical reaction in which two reactants combine to yield a larger product Combine Hydrolysis Reaction a molecule of water spits to provide the H and OH needed to complete the resulting monosaccharide Hydrolysis reactions commonly occur during digestion Complex Carbohydrates 3 types of polysaccharides 1 Glycogen not a significant source of a carbohydrate only a limited extent is found in meats and NOT at all in plants human body stores glucose as glycogen in muscles enzymes respond by attacking the branches of glycogen simultaneously making a surge of glucose available 2 starches plants store glucose in the form of starch long branched or un branched chains of thousands of glucose molecules linked together found in grains legumes rice root crops ext 3 Fibers dietary fibers are the structural parts of plands they are not digested there are 7 types of dietary fibers 1 Soluble fibers dissolve in water 2 Viscous fibers form gels 3 Fermentable digested by bacteria in the colon 4 Insoluble fibers do not dissolve in water found mostly in whole grains promote bowl movements and alleviate constipation 5 Functional fibers added supplements in food ex cellulose in cereals 6 Resistant starches starches that escape digestion and absorption in the small intestine common in whole legumes raw potatoes and unripe bananas 7 Phytic Acid binds with minerals preventing their absorbtion ex of minerals include zinc iron calcium magnesium and copper Digestion and Absorption of Carbohydrates Step 1 Mouth chewing high fiber foods slows eating and stimulates the flow of saliva carbohydrates Amylase salivary enzyme that breaks down hydrolyzes Step 2 Stomach swallowed bolus mixes with the stomachs hydrochloric acid and protein digesting enzymes which inactivates salivary amylase Fibers do not break down in the stomach and delay gastric emptying thereby providing a feeling of fullness and satiety Step 3 Small Intestine performs most of the carbohydrate digestion pancreatic amylase enters via the pancreatic duct and continues to break down the polysaccharides to shorted glucose chains and maltose Specific enzymes break down specific disaccharides o Maltase breaks down maltose into 2 glucose molecules o Sucrase breaks down sucrose into 1 glucose and 1 fructose o Lactase breaks down lactose into 1 glucose and 1 galactose At this point all polysaccharides into monosaccharides Step 4 Large Intestine within 1 to 4 hours all sugars and starches have been digested only the fibers remain in the digestive tract Fermenting fibers caused by bacteria in the GI tract produce water gas and short chain fatty acids Lactose Intolerance Symptoms bloating abdominal discomfort diarrhea Definition a condition that results from inability to digest milk sugar Lactase deficiency a lack of the enzyme required to digest lactose Prevalence lowest among scandinavians and northern eurpoeans highest among native north americans and southeast asians Kefir a fermented milk created by adding bacteria that breaks down lactose Making Glucose from Protein Gluconeogenesis the making of glucose from a non carbohydrate source Protein sparing action the action of carbohydrate in providing energy that allows protein to be used for other purposes Ketone bodies the product of the incomplete breakdown of fat when glucose is not available in the cells Ketosis a condition that disturbs the body s normal acid base balance Fat cells an store in unlimited quantites Blood Glucose Maintiang glucose homeostasis the body must maintain blood glucose within limits that permit the cells to nourish themselves if a persons glucose falls below normal a person may experience dizziness and become weak if the blood glucose level is high a person may experience fatigue Regulating Hormones Insulin a hormone secreted by the pancreas in response to increased blood glucose concentration The primary role of insulin is to control the transport of glucose from the bloodstream into the muscle and fat cells Glucagon a hormone that is secreted by special cells in the pancreas in response to low blood glucose concentration and elicits release of glucose from liver glycogen Glucagon raises blood glucose Epinephrine a hormone secreted by the adrenal gland that regulates the stress response Diabetes a chronic disorder of carbohydrate metabolism usually resulting from insufficient insulin Type 1 diabetes less common type of diabetes in which the pancreas fails to produce insulin Type 2 diabetes considered an autoimmune disorder the more common type in which the cells fail to respond to insulin Glycemic
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