Gastrointestinal Nursing.pdf

The Pancreas 127by separate capillary beds. Blood drains from the pancreas via the portal veinto the liver or into the splenic circulation by the superior mesenteric andsplenic veins.Nerve supply to the pancreasCholinergic preganglionic fibres of the vagus nerve enter the pancreas. Theysynapse with postganglionic cholinergic nerve fibres, which lie in pancreatictissue and innervate both acinar and islet cells. Post-ganglionic sympatheticnerves from the coeliac and superior mesenteric plexi innervate vascular flowand control pain sensations and enzyme secretion in the pancreas. Parasympatheticfibres control exocrine and endocrine functions.Pancreatic juiceThe exocrine acinar cells secrete between 500 and 1000 ml of pancreatic juiceeach day. Pancreatic juice has two types of secretion, an enzyme-rich portionand an aqueous alkaline-rich portion. It is a colourless fluid and has a pHof 8.1–8.3. It consists of water, bicarbonate, sodium, potassium, chloride andcalcium. The function of the alkaline nature of pancreatic juice, together withother alkaline secretions, namely bile and intestinal juice, is to neutralise theacidic chyme arriving from the stomach.This neutralising function is important for three main reasons:• Pancreatic enzymes require a neutral or slightly alkaline environment foroptimal activity.• The absorption of fat depends upon the formation of micelles in the intestinallumen, a process which will only take place at a neutral or slightlyalkaline pH.• It protects the intestinal mucosa because excess acid in the duodenum candamage the mucosa and lead to ulceration.Pancreatic juice enters the duodenum with secretions of the biliary system atthe ampulla of Vater.Pancreatic enzymesThere are three main types of enzyme present in pancreatic juice:• Amylases, which break down carbohydrates into glucose and maltose.• Lipases, which are important in the early stages of fat breakdown.• Proteases, including trypsinogen, the precursor of proteolytic trypsin.