Digestion as a Process
ALIMENTARY, MY
DEAR WATSON…
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)
Carbohydrates
Sugars
Proteins
Fats
Glycerol
Glucose  G3P  Pyruvate
Glycolysis
Fatty Acids
Amino acids
Acetyl CoA
Citric Acid
Cycle
Your task?
 Using your textbook, fill out the chart on digestive
structures

Describe their role in digestion