Cells in focus
Pancreatic acinar cell: Its role in acute pancreatitis

https://doi.org/10.1016/j.biocel.2005.12.001Get rights and content

Abstract

The pancreatic acinar cell is the functional unit of the exocrine pancreas. It synthesizes, stores, and secretes digestive enzymes. Under normal physiological conditions, digestive enzymes are activated only once they have reached the duodenum. Premature activation of these enzymes within pancreatic acinar cells leads to the onset of acute pancreatitis; it is the major clinical disorder associated with pancreatic acinar cells. Although there have been major advances in our understanding of the pathogenesis of this disease in recent years, available treatment options are still limited to traditional nonspecific and palliative interventions. Novel therapeutic strategies have been suggested based on ongoing research in the physiology and pathophysiology of the disease; these include the administration of systemic antibiotics, antioxidants, cytokine antagonists, and more recently, inhibition of the renin–angiotensin system. Notwithstanding this promising development, most of these potential therapies are still in an experimental stage or clinical trial. Further investigation is needed to prove the efficacy of these novel treatment modalities.

Introduction

The pancreas has two distinct functional portions: the exocrine and the endocrine pancreas. The endocrine pancreas, consisting of pancreatic islet cells that produce insulin, glucagon, somatostatin, and pancreatic polypeptide serves to maintain the body's glucose homeostasis. The exocrine pancreas is structurally analogous to a bunch of grapes; this architecture contains microscopic, blind-ended tubules that are surrounded by polygonal acinar cells and these tubules are organized into lobules called acini. The primary function of the acini is to synthesize and secrete hydrolytic enzymes which empty into the duodenum for the digestion of our daily foodstuff. Each acinus consists of a small cluster of secretory epithelial cells that form a small central lumen, called intercellular canaliculi. Each acinar cell has a round pyramid-like shape. The acinar cell is highly polarized with two plasma membrane domains. The basolateral membrane is large and located at the acinar periphery; the apical membrane (less than 10% of total surface area of the cell) faces the acinar lumen that connects with a tiny intercalated duct. The digestive enzymes are stored in secretory granules which are concentrated near the apical membrane of the cell. The acini drain into the intercalated ducts, and groups of the intercalated ducts converge into larger intralobular ducts, which in turn drain into much larger extralobular ducts; the latter form a main collecting duct which empties into the duodenum (see Fig. 1). However, the accuracy of the traditional acinar structural model of strictly independent acini has been called into question. There are light and electron microscopy findings, suggesting that the exocrine pancreas may not be organized into true acinar units. Instead, the arrangement may consist of a complexly curving and branching system of tubules which anastomose between adjacent acini (Bockman, 1980).

Section snippets

Cell origin and plasticity

Early in the fifth week of intrauterine life in humans, the pancreas arises from the abdominal foregut as dorsal and ventral diverticular buds. The ventral bud rotates to fuse with the dorsal bud which ultimately forms the splenic portion, i.e. body and tail. The ventral duct fuses with the distal portion of the dorsal duct to form the head or duodenal portion of the pancreas.

Some studies have suggested that there is a common pancreatic progenitor which gives rise to both exocrine (acinar) and

Functions

The major function of pancreatic acinar cells is to synthesize, store and secrete digestive enzymes so as to catalyze the hydrolysis of food constituents into absorbable forms. Pancreatic acinar cells secrete three major categories of digestive enzymes; they are α-amylase, lipase and proteases which are responsible for the hydrolysis of carbohydrates, fats and proteins, respectively. The synthesis of the digestive enzymes begins at the ribosomes located in the cytosol of the cell. To enable

Associated pathologies

The clinical disorders associated with pancreatic acinar cell dysfunction include acute pancreatitis, chronic pancreatitis, autoimmune pancreatitis, pancreatic exocrine insufficiency, and pancreatic neoplasia. Among them, acute pancreatitis is the most common human disease of the pancreas. Therefore the present review focuses on the pathophysiology and current clinical management of acute pancreatitis. Although the condition is usually mild, about 25% of patients will develop complications such

Acknowledgements

This work was fully supported by the Competitive Earmarked Research Grant from the Research Grants Council of Hong Kong (Project Nos. CUHK4364/04M and CUHK4537/05M), awarded to PSL.

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