Unit 5 Notes: The Stomach

The stomach

• The stomach is a dilated part of the alimentary canal between the esophagus and the small intestine.

• It is a muscular sac.

• It is a J-shaped.

Stomach Size• When it is expanded, the

stomach measures about 10 inches by 4 inches.

• Its capacity holds

about one quart.

The stomachThe stomach is divided into four regions:

1. The cardia, which surrounds the opening of the esophagus into the stomach.

2. The fundus of stomach, which is the area above the level of the cardial orifice.

3. The body of stomach, which is the largest region of the stomach.

4. The pyloric part, which is divided into the pyloric antrum and pyloric canal and is the distal end of the stomach.

The stomach

• Openings:

–Gastroesophageal: To esophagus

–Pyloric: To duodenum

The stomach

Sphincters

The cardiac sphincter (lower esophagus sphincter) closes off the top end of the stomach.

The pyloric sphincter closes off the bottom.

Where is our Stomach located?• The stomach is located between the

Esophagus and the Duodenum above the small intestines.

• The Esophagus is the passage between the mouth and the stomach.

• The Duodenum is the first part of the small intestines.

• The stomach is on the upper left quadrant of the abdomen and lies against the diaphragm.

The above photo shows the Esophagus to the stomach.

Food travels through the Esophagus into the Stomach and through the small intestines.

The stomach

Stomach Anatomical Relation

(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.

Stomach Process: 3 phase

1. Cephalic- Sense of smell and sight, as well as thinking about food sends a message to the brain indicating that the stomach is hungry.

2. Gastric- Food enters the stomach and stretches and sends impulses to the brain, then the gastrin begins secreting.

3. Intestinal- Food enters the small intestines and is digested.

pH video

(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

Description• The stomach is an expanded J-shapedJ-shaped

organ in the upper left region of the abdominal cavity.

• It is continuous with the esophagus superiorly and empties into the duodenum of the small intestine inferiorly.

• It continues the mechanical and chemical digestion of the bolus. After the bolus has been completely processed in the in the stomach, stomach, the product is called chyme.

(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

When empty, the stomach collapses inward, throwing its mucosa into large, longitudinal folds called rugae (roo’ge).

Gastric emptying

• Solid food remains in the stomach until it has been broken down into small particles (diameter of !1mm) and suspended in chyme.

• The chyme then passes to the duodenum.

• The time required for 50% of the ingested volume to leave the stomach varies, for instance:– 10—20 min for water and – 1–4 hours for solids (carbohydrates, proteins,

fats).

Indigestible substances• Indigestible substances (bone, fiber, foreign bodies)

do not leave the stomach during the digestive phase.

• Special contraction waves called migrating motor complexes (MMC) pass through the stomach and small intestine roughly every 1.5 hours during the ensuing interdigestive phase, as determined by an intrinsic “biological clock”.

• These peristaltic waves transport indigestible substances from the stomach and bacteria from the small intestine to the large intestine.

Mechanical Digestion• The walls of stomach have several layers

of smooth muscle. There are three layers of muscle, when food is present, these muscles work together to churn the content of stomach.

• You have probably heard your stomach “growl” when it has been empty for some times. These sounds are made by the contraction of smooth muscles that form the walls of stomach.

Chemical Digestion• Gastric fluid carries out chemical

digestion in the stomach.

• Gastric enzymes:– Pepsin splits complex protein

molecules into shorter chains of amino acids.

– Hydrochloric acid in the stomach not only ensure the low pH, but also dissolves minerals and kills bacteria that enter the stomach along with food.

Gastrectomy• About half of the patients subjected to

total gastrectomy experience weight loss.

• Malabsorption, particularly fat malabsorption, is a common feature after total gastrectomy. This may be due to shortened intestinal transit time and small bowel bacterial overgrowth, but is less often due to diarrhea or pancreatic exocrine insufficiency.

Total and subtotal

• In a total gastrectomy, the intestine is joined to the end of the esophagus, whilst

• In a partial (or sub-total) gastrectomy the intestine is joined to the remaining healthy stomach.

sub

Total

Common After-Effects of Gastrectomy

• Prolonged period of recovery.• Reduces size of the food reservoir – this can

lead to reduced food intake and weight loss.• Vitamin B12 not available from diet – so B12

will be needed by injection.• No stomach acid means that the stomach is

more susceptible to infections.• Rapid movement of food to small intestine –

this causes ‘dumping syndrome’.

Health Problems• Many problems can

occur if there are issues with your digestive system:– Ulcers– Gastritis– Gastroenteritis– Gastroesophageal

reflux– Stomach Cancer– Black Stool

Causes– Ulcers-affects is the nerves that is around it. It

becomes agitated and causes pain.– Gastritis-  inflammation, irritation, or erosion of

the lining of the stomach– Gastroenteritis- causes irritation and

inflammation of the stomach and intestines– Gastroesophageal reflux (GERD)-affects the

lower esophageal sphincter– Stomach Cancer- disease in which stomach cells

become cancerous– Black Stool- darkening or blackness of stool

Review Video

Comparison between different animals