Digestion as a Process

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, starchesStarts in mouth, w/ salivary amylaseMainly 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 lactaseLactose passes undigested into large

intestineHere, 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 digestionStarts in stomachCompleted 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 enzymeEmulsifies fats (breaks fat droplets into very small droplets)

Pancreatic lipaseChanges 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)

Carbohydrates

Sugars

Glucose G3P Pyruvate Glycolysis

Fats

Glycerol Fatty Acids

Acetyl CoA

Proteins

Amino acids

Citric Acid Cycle

Your task?

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