ALIMENTARY, MY DEAR WATSON… Digestion as a Process

Digestion Def: Changing of foods to a form that can be absorbed and used by cells Occurs in alimentary canal Consists of both mechanical and chemical types

Mechanical digestion Break down food into tiny particles Mix them with digestive juices (produces a bolus) Move them along digestive tract Eliminates digestive wastes from the body

Involves : Chewing (mastication) Swallowing (deglutition) Peristalsis (wave-like contractions that move down a tube) Defecation (elimination)

Chemical digestion Breaks up large, non-absorbable food molecules into compounds having smaller molecules Can then pass through intestinal mucosa into blood/lymph Brought about by digestive enzymes

Carbohydrate digestion (Monosaccharide) (Disaccharide) (Polysaccharide)

Carbohydrate digestion Carbs = Sugars, starches Starts in mouth, w/ salivary amylase Mainly in small intestine  Pancreatic amylase – changes starches to maltose (disaccharide)  Intestinal juice enzymes  Maltase – changes maltose to glucose*  Sucrase – changes sucrose to glucose*  Lactase – changes lactose to glucose*  *Monosaccharide

Lactose intolerance?

Lactose Intolerance Individual cannot synthesize lactase Lactose passes undigested into large intestine Here, bacteria (which have lactase) break down lactose, resulting in a “double whammy”  Releases gas  Plus…  Lactose is “osmotically active”  So… it draws water into your intestine… causing diarrhea.

Protein digestion Starts in stomach Completed in small intestine  Gastric juice enzymes, rennin (in infants) and pepsin, partially digest proteins  Pancreatic enzyme, trypsin, completes digestion of proteins to amino acids  Intestinal enzymes, peptidases, complete digestion of partially digested proteins to amino acids

Fat digestion Bile  Not an enzyme  Emulsifies fats (breaks fat droplets into very small droplets) Pancreatic lipase  Changes emulsified fats to fatty acids and glycerol in small intestine

Absorption Definition: Digested food moves from intestine into blood or lymph Enhanced by:  Plica(folds in the lining mucosa)  Villi  Microvilli

Absorption site: Foods (and most water) absorbed within small intestine Some water also absorbed through large intestine

Where does it all go? Food (such as a peanut)CarbohydratesSugars Glucose  G3P  Pyruvate Glycolysis FatsGlycerolFatty AcidsAcetyl CoAProteinsAmino acids Citric Acid Cycle

Your task? Using your textbook, fill out the chart on digestive structures  Describe their role in digestion