Chapter 17 – Part 2

The Stomach

Digestion Summary

Stomach muscles contract and relax to mechanically break down the food

It also mixes the food with gastric juice and hydrochloric acidThe acid kills germs in the food and

creates optimal pH for enzymes.The gastric juice contains the protease enzyme PEPSIN to digest protein into amino acids.

Food spends about 3-4 hours in here.

Gastric Absorption

• some water• certain salts• certain lipid-soluble drugs• alcohol

Stomach Muscles: Longitudinal, Circular, Oblique

Mixing and Emptying Actions

Why does your stomach growl???

Radiograph of Stomach

Stomach Lining Gastric Glands secrete gastric juices/acid

(parietal cells)

PEPSIN  - most important digestive enzyme for breaking down food (chief cells)

Mucus prevents stomach from digesting itself

  

 

Lining

Chyme - paste, after food has been broken down, released then into the duodenum via the pyloric sphincter valve

Enzymes work best at one pH. This pH is different for each different enzyme.

If the pH goes too low (more acidic) or too high (more alkaline), the enzyme will not work as effectively.

Enzymes and pH

Gastric Secretions• pepsinogen• from chief cells• inactive form of pepsin

• pepsin• from pepsinogen in presence of HCl• protein splitting enzyme

• hydrochloric acid• from parietal cells• needed to convert pepsinogen to pepsin

• intrinsic factor• from parietal cells• required for vitamin B12 absorption

• mucus• from goblet cells and mucous glands• protective to stomach wall

Phases of Gastric Secretions• Cephalic phase• triggered by smell, taste, sight, or thought of food• nerve impulses trigger gastric juice secretion

• Gastric phase• triggered by presence of food in stomach• gastrin released •gastric juice secreted and mixes with food

• Intestinal phase • triggered by movement of food into small intestine• intestinal cells release intestinal gastrin• secretion of more stomach gastric juice promoted

Gastrin: • Peptide hormone• Increases secretory

activity of gastric glands

• Promote mucus production

• Stimulates cell growth in mucosa

Regulation of Gastric Secretions

Both neurally

and hormonally controlled.

Enterogastric Reflex

17

Regulates the rate at which chyme leaves the stomach

Stomach Ulcers

Stress and diet play a role in severity but are NOT the cause.

• The bacterium associated with stomach ulcers is quite common.

• About ½ of all people in the U.S. under the age of 60 is likely to have helicobacter pylori.

Lactose Intolerance

  Inability to digest milk, can cause stomach upset

Gastric Bypass Surgery

http://www.hurtbyadoctor.com/Gastric-Bypass-Surgery-Malpractice-Lawsuits-Information-Home.htm