Digestive Glands — Core Principles

Core Principles

Digestive glands are specialized organs or cell clusters that produce and secrete digestive juices into the alimentary canal, facilitating chemical digestion. The major glands include the salivary glands, gastric glands, liver, pancreas, and intestinal glands.

Salivary glands (parotid, submandibular, sublingual) secrete saliva containing salivary amylase for starch digestion and lysozyme for antimicrobial action. Gastric glands in the stomach lining secrete gastric juice, comprising HCl (for activation of pepsinogen and killing microbes), pepsinogen (for protein digestion), mucus (for protection), and intrinsic factor (for Vitamin B12 absorption).

The liver, the largest gland, produces bile, which emulsifies fats, aiding lipase action. The pancreas, a mixed gland, secretes alkaline pancreatic juice with enzymes like pancreatic amylase, lipase, and proteases (trypsinogen, chymotrypsinogen) for comprehensive digestion of carbohydrates, fats, and proteins.

Finally, intestinal glands (Crypts of Lieberkühn) produce succus entericus, containing disaccharidases, dipeptidases, and lipases, completing the digestion of food into absorbable monomers. These glands are regulated by both neural and hormonal mechanisms, ensuring efficient and timely secretion of digestive enzymes.

Important Differences

vs Exocrine Pancreas vs. Endocrine Pancreas

Aspect	This Topic	Exocrine Pancreas vs. Endocrine Pancreas
Function	Produces digestive enzymes and bicarbonate (pancreatic juice) for chemical digestion in the small intestine.	Produces hormones (e.g., insulin, glucagon) that regulate blood glucose levels and other metabolic processes.
Secretory Cells	Acinar cells (arranged in acini).	Islets of Langerhans (alpha, beta, delta cells, etc.).
Secretion Pathway	Secretions released into ducts (pancreatic duct) that empty into the duodenum.	Hormones secreted directly into the bloodstream (ductless glands).
Target	Lumen of the small intestine (for digestion).	Distant target cells throughout the body (via blood).
Volume of Gland	Constitutes the vast majority (approx. 99%) of the pancreatic tissue.	Constitutes a small percentage (approx. 1-2%) of the pancreatic tissue.

The pancreas is a unique 'heterocrine' gland, performing both exocrine and endocrine functions. The exocrine pancreas, comprising acinar cells, is responsible for producing and secreting pancreatic juice, a potent mixture of digestive enzymes (for carbohydrates, proteins, and fats) and bicarbonate, into the duodenum via ducts. This is crucial for chemical digestion. In contrast, the endocrine pancreas, consisting of the islets of Langerhans, is ductless and secretes hormones like insulin and glucagon directly into the bloodstream, which are vital for regulating blood sugar and overall metabolism. Understanding this dual role is key for NEET.