Digestion
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Liz Lauben
Introduction
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Digestion is defined as the breakdown of
nutrients
We consume:
Proteins
Carbohydrates
Fats
These are broken down into their simplest
forms
Liz Lauben
From Beginning to End
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Mouth
Esophagus
Stomach
Small intestine
Large intestine
Anus
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Mouth
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Mechanical digestion: the act of chewing
Carbohydrate digestion begins here
Saliva moistens food and contains the enzyme
Salivary Amylase – breaks down complex carbs
into simple sugars
Chemical Digestion: enzymes breaking down
carbohydrates
Ball of moistened, partially digested food, known
as the “BOLUS”, moves into the esophagus
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Esophagus
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Long tube through
which “bolus” moves
down into the
stomach
The contraction of
muscles pushes the
food down – known
as PERISTALSIS
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Stomach
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Protein digestion begins here
Gastric Glands: Parietal Cells
Chief Cells
Chief Cells release HCl, the acidity kills foreign
material and bacteria
Parietal Cells release the inactive enzyme
Pepsinogen. This combines with HCl to create
active form: Pepsin
Pepsin breaks down proteins into smaller
polypeptide chains or amino acids
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Just a Reminder…
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Both types of digestion are occurring in
the stomach: Mechanical and Chemical
The churning of the stomach is considered
mechanical digestion
The enzyme activity is considered
chemical digestion
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Small Intestine
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Continuation of Carbohydrate and Protein Digestion;
beginning of Fat digestion
LIVER: releases bile that breaks down fats into fatty
acids
PANCREAS: releases pancreatic juices, one of which
completes protein digestion (proteins to amino acids)
and carbohydrate digestion (complex sugars into simple
monosaccharides)
Absorption of simple nutrients through villi occurs here
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Large Intestine
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Unabsorbed material moves through large
intestine, where water and salt are
absorbed
This removal of liquid forms solid-like
feces
Feces is stored in the colon
Feces is removed from the body, via the
anus
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10
Liz Lauben