Unit 5 Notes: The Stomach

(1) About The Stomach• Stomach can contain up to 1.5L of food without

pressure changes.– Feelings of discomfort come from irritants + too

much food

• Stomach composed of excess tissue Folds of Tissue = Rugae– Folds allow the stomach to expand– Folds also contain secretion glands

• Food sits in the stomach for 3-4 hours– Depends on Amount & Type of food

(2) Dig. In The Stomach• Mechanical Digestion:

–Peristaltic churning of stomach muscle breaks apart bolus.

–Triggered by release of serotonin from rugae

• Chemical Digestion:–Gastric Juice contains enzymes

and acid that breaks down bolus.

(3) Release of Gastric Juice• Gastrin (hormone) released from G-

Cells within Rugae:–Triggered by smell + taste of food–Triggered by increase in pH

• Gastrin stimulates release of HCl = Decreasing pH:–Proteins & Carbohydrates

Metabolized–Small & Large Intestine stimulated

(4) Gastric JuiceContains…• HCl = Hydrochloric Acid • Pepsin = Enzyme = Breaks down

protein• Rennin = Enzyme = Breaks down

protein• Muccin = Mucus = Lubricate Food

Mass

(5) 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.

(6) Leaving The Stomach• The mass leaving the stomach is called

“Chyme”:–Mostly liquid Liquids leave first!–Solids are left behind until broken

down

• Approximately 3mL of food leaves at one time….–Food Exits the Pyloric Sphincter–Chyme dumped into Small Intestine