Anatomy
and physiology
Surgical
anatomy
The name ‘pancreas’ is derived from the Greek ‘pan’ (all) and ‘kreas’
(flesh). It was originally thought to act as a cushion for the stomach. The
gland weighs approximately 80 g and is situated retroperitoneally. It is divided
into a head, which
There are nine key processes that occur during pancreatic embryogenesis (Table 55.1).
Pancreatic acinar tissue is organised into
lobules. The main duct ramifies into intralobular and interlobular ducts,
ductules
and, finally, acini. Acinar cells are clumped around a central lumen to form an
acinus which communicates with the duct system. The pancreas thus consists of a
network of fine ducts lined by secretory cells. The islets of Langerhans are
distributed throughout the pancreas. Islet cells consist of differing cell
types: 75 per cent are B cells (producing insulin), 20 per cent A cells
(producing glucagon), and the
Surgical
physiology
In response to a meal, the pancreas secretes digestive enzymes in an
alkaline (pH 8.4) bicarbonate-rich fluid. Spontaneous secretion is minimal,
the hormone secretin which is released from the duodenal mucosa evokes a
bicarbonate-rich fluid. Cholecystokinin-pancreozymin (CCK) is released from the
duodenal mucosa in response to food: CCK produces no increase in the volume of
secretion, but is responsible for enzyme secretion. Vagal stimulation
increases volume. Protein is synthesised at a greater rate (per gram of tissue)
in the pancreas than in any other tissue, with the possible exception of the
lactating mammary gland. About 90 per cent of this protein is exported from the
acinar cells as a variety of digestive enzymes. Approximately 6—20 g of digestive
enzymes enter the duodenum each day. Nascent proteins are synthesised as pre
proforms and during their transit through the rough endoplasmic reticulum and
Golgi cisterni, the newly synthesised proteins undergo modification in a
sequence of steps. The proteins move from the rough endothelial endoplasmic
reticulum to the Golgi complex, where lysosomes and mature zymogen storage
granules containing proteases are stored, and move to the ductal surface of the
cell from which they are extruded by exostosis. During this phase the
proteolytic enzymes are in an inactive form, the maintenance of which is
important in preventing pancreatitis.