KEY POINTS

The Salivary Glands

1. Saliva moistens, lubricates, and partially digests food.

2. Salivary secretions originate in the gland acini and are modified in the collecting ducts.

3. Salivary glands are regulated by the parasympathetic nervous system.

4. Ruminant saliva is a bicarbonate-phosphate buffer secreted in large quantities.

Gastric Secretion

1. Depending on the species, there may be two general types of gastric mucosa: glandular and nonglandular.

2. The gastric mucosa contains many different cell types.

3. The gastric glands secrete hydrochloric acid.

4. Pepsin is secreted by gastric chief cells in an inactive form and is subsequently activated in the gut lumen.

5. The parietal cells are stimulated to secrete by the action of acetylcholine, gastrin, and histamine.

The Pancreas

1. Pancreatic exocrine secretions are indispensable for the digestion of the complex nutrients: proteins, starches, and triglycerides.

2. Acinar cells secrete enzymes, whereas centroacinar cells and duct cells secrete a sodium bicarbonate solution.

3. Pancreatic cells have cell surface receptors stimulated by acetylcholine, cholecystokinin, and secretin.

Bile Secretion

1. The liver is an acinar gland with small acinar Iumina known as canaliculi.

2. Bile contains phospholipids and cholesterol maintained in aqueous solution by the detergent action of bile acids.

3. The gallbladder stores and concentrates bile during the periods between feeding.

4. Bile secretion is initiated by the presence of food in the duodenum and stimulated by the return of bile acids to the liver.