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Understanding the Digestion Process: From Food to Absorption

Digestion transforms food into absorbable forms through both mechanical and chemical processes within the alimentary canal. Mechanical digestion involves chewing, swallowing, peristalsis, and defecation, while chemical digestion breaks down complex molecules into smaller, absorbable compounds using digestive enzymes. Carbohydrate digestion begins in the mouth, with starches converted to sugars in the small intestine, whereas proteins are partially digested in the stomach and completed in the small intestine. Fats are emulsified by bile and further digested by pancreatic lipase. Absorption occurs mainly in the small intestine through villi and microvilli, allowing nutrients to enter the bloodstream.

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Understanding the Digestion Process: From Food to Absorption

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  1. Digestion as a Process Alimentary, my dear watson…

  2. 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

  3. 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

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

  5. 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

  6. Carbohydrate digestion (Monosaccharide) (Disaccharide) (Polysaccharide)

  7. 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

  8. Lactose intolerance?

  9. 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.

  10. 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

  11. 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

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

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

  14. Where does it all go?

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

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