Acinar cells are cells of the exocrine pancreas that synthesize, store, and secrete digestive enzymes. They produce almost all the enzymes required for digestion in the small intestine, including endo- and exo-proteases, nucleases, lipases, and glycosidases. The rate of protein synthesis in acinar cells is higher than that of any other cells in the adult body, and they are highly adapted for this function.
What is an Acinar Cell?
Acinar cells are specialized cells of the exocrine pancreas whose function is to produce, secrete, and store digestive enzymes. The name ‘acinar’ (from the Latin word ‘acinus,’ meaning ‘berry’) refers to the arrangement of these cells in the pancreas, where they are clustered in grape-like bunches called acini. The acini secrete all the enzymes required for the digestion of carbohydrates, proteins, and lipids in the small intestine.
Function of the Exocrine Pancreas
The primary function of the pancreas is to produce enzymes for the digestion of food molecules. Around 95% of the pancreas consists of exocrine tissue, which includes acinar cells and secretes digestive enzymes. The remainder of the pancreas is endocrine tissue, which is composed of endocrine cells called the Isles of Langerhans. The primary function of the endocrine pancreas is to regulate blood sugar levels by releasing hormones such as insulin into the bloodstream.
Structure and Function of Acinar Cells
Acini in the pancreas consist of groups of acinar cells, which synthesize and secrete enzymes for the digestion of dietary carbohydrates, proteins, and lipids. Acinar cells are highly adapted for the production, storage, and secretion of digestive enzymes.
Pancreatic acinar cells produce almost all of the enzymes required for food digestion in the small intestine, including endo- and exo-proteases, nucleases, lipases, and glycosidases. Therefore, they synthesize proteins at a very high rate; in fact, they produce and secrete more proteins than any other cell in the adult body. Acinar cells are specially adapted for this function and contain abundant rough endoplasmic reticulum (RER) for protein production and processing.
Over 90% of the proteins produced in acinar cells are packaged into specialized organelles called zymogen granules. Digestive enzymes are stored in the zymogen granules until they are needed, at which point they are secreted from the acinar cells by exocytosis.
Zymogen granules have an acidic pH, which inhibits the activity of digestive enzymes and helps to prevent potential digestion of the pancreatic tissues. Enzymes may also be stored in an inactive form to minimize the risk of damage to the pancreas.
Enzymes are stored in the zymogen granules of acinar cells until they are required for digestion. The contents of the zymogen granules are released by exocytosis and travel through the pancreatic duct to the duodenum (i.e., the first section) of the small intestine. Digestive enzymes are normally only activated once they reach the duodenum.
Acinar Cells and Acute Pancreatitis
Acinar cells are linked to acute pancreatitis; a condition in which the pancreas becomes painfully inflamed. Gallstones are the most common cause of acute pancreatitis. They block the ducts that connect the pancreas to the gallbladder, which leads to an accumulation of enzymes in the pancreas. The enzymes then begin to digest the pancreatic tissue and cause severe inflammation.
Acute pancreatitis is most commonly associated with gallstones and/or excessive alcohol consumption. However, studies suggest that acinar cells may play a key role in the onset of the condition. In healthy individuals, digestive enzymes are not activated until they reach the duodenum of the small intestine. Premature activation of these enzymes within the acinar cells leads to the development of pancreatitis and inflammation of the surrounding tissues.