Notes: The Stomach

Tuesday 1-5-2010

(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.

– 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

(3) Contraction & Churning

Stomach composed of smooth muscle:– Contains 3 layers of muscle = STRONG– Contracts via peristalsis

Peristalsis used to Toss & Churn (not squeeze through).– Like Shake & Bake

Contractions stimulated by release of Serotonin from Rugae.

(4) 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

(5) Gastric Juice

HCl = Hydrochloric Acid Pepsin = Enzyme = Breaks down proteinRennin = Enzyme = Breaks down proteinMuccin = 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”:– 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