4.3 Secretory Functions of Alimentary Tract

Salivary Glands and Functions

• Salivary amylase is the enzyme in saliva that digests starches.
• Mucin in saliva primarily functions to lubricate food for easier swallowing.
• The parotid gland produces saliva that is 25% serous secretion only.
• The glossopharyngeal nerve stimulates the parotid gland for saliva secretion.
• Sympathetic stimulation decreases saliva secretion, leading to a dry mouth.

Esophagus and Stomach Secretions

• The esophagus secretes mucus to facilitate the passage of food and protect against abrasion.
• Oxyntic glands secrete an acidic solution with a pH around 1-3 when stimulated.
• Parietal cells in the oxyntic glands are responsible for secreting hydrochloric acid and intrinsic factor.
• Pyloric glands are located in the antrum of the stomach.
• Enterochromaffin-like (ECL) cells secrete histamine in the oxyntic glands.

Small Intestine Functions

• During the interdigestive period, oxyntic glands primarily secrete hydrochloric acid and intrinsic factor.
• Nonoxyntic glands primarily resemble mucous secretions.
• Goblet cells in the small intestine secrete protective mucus in response to tactile stimuli and vagal stimulation.
• The primary function of the small intestine is nutrient absorption.
• Brunner's glands secrete protective mucus in the early duodenum in response to the gastrointestinal hormone secretin.
• Brush border enzymes in the small intestine, like peptidases, split proteins into amino acids.

Bile and Gallbladder Function

• Gastric ulcers have a high rate of incidence in the antrum and pylorus regions of the stomach.
• Psychological stress can lead to the development of stress ulcers.
• Bile acids play a crucial role in emulsifying fats for digestion and absorption.
• Bile acids are synthesized from cholesterol and secreted into bile conjugated to glycine or taurine.
• The primary route for the transportation of absorbed bile acids back to the liver is through enterohepatic circulation.
• Cholecystokinin (CCK) is the hormone that stimulates gallbladder contraction and emptying, especially in response to fatty foods.
• Bile secretion decreases when food does not contain fat; it is less stimulated and may be reduced.

Pancreas and Its Secretions

• The main role of the endocrine pancreas acinus is to produce digestive enzymes.
• Amylase is the most abundant enzyme secreted by acinar cells in the pancreas.
• Pancreatic zymogens stored in acinar cells are activated by enteropeptidase in the small intestine.
• Autodigestion of the pancreas can occur in cases of pancreatitis or blockage of pancreatic ducts.
• The secretion of pancreatic enzymes is controlled by the hormone secretin and cholecystokinin.
• Secretin stimulates the pancreas to produce bicarbonate to neutralize acidic chyme entering the small intestine.
• The accessory pancreatic duct (Santorini) facilitates drainage of pancreatic secretions, particularly when the main duct is blocked.

Test your knowledge on the exocrine pancreas secretion and pancreatic digestive enzymes. Learn about how compound alveolar glands secrete into ducts, the structure of acinar cells, and the digestive enzymes secreted by acinar cells for proteins.