Structural features

Length: 12-15 cm; weight around 100 g

It is a compound acinar gland, with at least 85% of the gland being comprised of exocrine secretory cells.

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The acinus is the functional unit. It consists of pyramidal shaped glandular cells with their apices facing the lumen of the acinus. The acinar cells are arranged in a semicircle around the lumen.

Acinar cells have the following characteristics:

Highly polarised, with functional and structural differences in the apical and basolateral plasma membrane domains;

Well developed Golgi complexes and rough endoplasmic reticulum, designed for the synthesis and storage of secretory proteins;

Zymogen or storage granules are found in the apical (luminal) side of the cytoplasm. These fuse with the luminal membrane of acinar cell at the time of secretion.

The pancreas secretes about 1 litre of juice per day, which consists of water, electrolytes and digestive enzymes. The secretion has two major functions, the intra-luminal digestion of macronutrients and the maintenance of a near neutral intra-luminal pH by the action of bicarbonate.

The pancreas is protected from autodigestion by its enzymatic products by virtue of the following mechanisms:

Synthesis of inactive proenzyme precursor zymogens;

Proteins secreted by the pancreas

Proteolytic enzymes

Endopeptidases: Trypsinogen Chymotrypsinogen Proelastase

Exopeptidases

Procarboxypeptidases - carboxypeptidase A and B

Lipolytic enzymes

Lipase

Phospholipase A2 Carboxyesterase

Amylolytic enzymes

Alpha-amylase

Nucleases

DNAase RNAase

Other enzymes Procolipase Trypsin inhibitor

Zymogen granules are sequestrated in acinar cells;

Acinar cells make trypsin inhibitor, which is co-packaged with trypsinogen in zymogen granules;

The activation site is within the duodenal lumen.

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