Download Notes: The Stomach

Tuesday 1-5-2010
Notes: The Stomach
(1) Overall Function
Break down “bolus” from esophagus.
 Metabolize ALL Carbohydrates.
 Begin Protein Metabolism.
 Turn “bolus” into liquid  Small Intestine

(2) The Stomach as a
Chamber

Stomach can contain up to 1.5L of food without
pressure changes.
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
Stomach composed of excess tissue  Folds of
Tissue = Rugae
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
Feelings of discomfort come from irritants + too much food
Folds allow the stomach to expand
Folds also contain secretion glands
Food sits in the stomach for 3-4 hours
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Depends on Amount & Type of food
(3) Contraction & Churning

Stomach composed of smooth muscle:
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Peristalsis used to Toss & Churn (not
squeeze through).
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Contains 3 layers of muscle = STRONG
Contracts via peristalsis
Like Shake & Bake
Contractions stimulated by release of
Serotonin from Rugae.
(4) Release of Gastric Juice

Gastrin (hormone) released from G-Cells
within Rugae:
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
Triggered by smell + taste of food
Triggered by increase in pH
Gastrin stimulates release of HCl =
Decreasing pH:
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Proteins & Carbohydrates Metabolized
Small & Large Intestine stimulated
(5) Gastric Juice
HCl = Hydrochloric Acid
 Pepsin = Enzyme = Breaks down protein
 Rennin = Enzyme = Breaks down protein
 Muccin = Mucus = Lubricate Food Mass

(6) Protein Metabolism
Proteins take a lot of Gastric Juice to
Metabolize.
 Breaking Down Proteins releases H+
ions.
 Decreases pH of stomach.
 G-Cells stop releasing gastrin  HCl
stopped.

(7) Exiting the Stomach

The mass leaving the stomach is called
“Chyme”:
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
Mostly liquid  Liquids leave first!
Solids are left behind until broken down
Approximately 3mL of food leaves at one
time….
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Food Exits the Pyloric Sphincter
Chyme dumped into Small Intestine