DIGESTION
The process of preparing your
food for absorption
What do you know about the
digestive system?
Digestion:
The Mouth
Chewing: physically breaks down food into
smaller components
Food stimulates salivary glands to release
saliva
Saliva contains amylase-breaks down starch
Saliva moistens food for easy swallow
Bolus: ball of chewed food mixed with saliva
DIGESTION:
THE PHARYNX
Area responsible for swallowing
During swallowing, air passage is
blocked by epiglottis
Blocks the food from entering the trachea
and the lungs
Bolus is directed down the esophagus
DIGESTION:
THE ESOPHAGUS
Connects the pharynx and the stomach
Bolus is moved towards the stomach by
a contractile movement called
peristalsis. Extra Credit??
Allows food to move through thoracic
cavity, through diaphragm, to peritoneal
cavity and the stomach
DIGESTION:
THE STOMACH
Food passes through a sphincter,
(esophageal sphincter) a valve
Bolus mixes with stomach secretions to
become chyme
HCl denatures proteins and kills bacteria
Mucus protects stomach wall from acid
Chyme released into small intestine through
pyloric sphincter
DIGESTION:
STOMACH
Stops salivary amylase and slows
lingual lipase activity (acid denatures
enzyme)
Starts protein digestion: pepsin
activated and starts protein digestion
What does the hydrochloric acid
of the stomach do to protein?
1. adds amino acids
to it
2. Denatures it
3. Provides
additional CHO
for it
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DIGESTION:
SMALL INTESTINE
20 feet in length
divided into three segments:
duodenum
jejunum
ileum
95% of digestion occurs in small intestine
Bile: made in liver, stored in gall bladder
Emulsifies fats
DIGESTION:
SMALL INTESTINES
Pancreas:
Secretes bicarbonate into duodenum to
neutralize stomach acid in the chyme
Secretes enzymes that act on
protein (proteases)
carbohydrate (carbohydrases)
lipids (lipases)
DIGESTION:
LARGE INTESTINES
Absorbs water and some minerals
Supports growth of bacteria that
produce Vitamin K
Supports growth of other bacteria that
partially breaks down fiber
We are then able to absorb some of the
breakdown products
DIGESTION:
CARBOHYDRATES
Begins in the mouth: salivary amylase
Amylase denatured in stomach
Small intestine: pancreatic enzymes
breakdown large CHO’s(starch) to smaller
Small intestines: brush border cells produce
disaccharidases (sucrase, maltase, lactase)
Breakdown sucrose, maltose, lactose
Absorption occurs in duodenum & jejunum
DIGESTION:
PROTEIN
Protein digestion begins in the stomach
Denaturation by HCl
Pepsin breaks large proteins into smaller peptides
Pancreatic enzymes introduced into the
duodenum
Break down peptides into amino acids, di- and tri-
peptides
Intestine enzymes breakdown to amino acids
What enzyme in the stomach starts
the chemical breakdown of protein?
1. lipase
2. carbohydrase
3. pepsin
4. Hydrochloric acid
5. sucrase
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DIGESTION:
LIPIDS
Mouth: Lingual Lipase, very little activity
Stomach: very little activity
Small Intestines: Major activity
Bilefrom gall bladder emulsifies
Enzymes from pancreas digest and makes
the products ready for digestion
monoglycerides, glycerol, fatty acids
absorbed into cells of microvilli
Digestion of CHO begins in the
mouth with
1. lingual lipase
2. salivary amylase
3. pancreatic source
enzymes
4. liver source
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Generally, where do the enzymes that break
down the large molecules such as starch, and
protein, come from?
1. The mouth
2. The stomach
3. The small
intestine
4. The pancreas
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