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SECTION G: PANCREAS

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Chapter 52

Pancreas Anatomy and Physiology

Taylor S. Riall

Key Points

1 The pancreas is both an endocrine and exocrine organ.

2 The primary function of the exocrine pancreas is to synthesize and secrete enzymes necessary for

digestion.

3 The primary function of the endocrine pancreas is regulation of body energy, primarily through

control of carbohydrate metabolism. Pancreatic endocrine hormones also play a critical role in the

complex regulation of pancreatic secretion and digestion.

4 Congenital anomalies of the pancreas largely result from failure of rotation or fusion of the ventral

and dorsal pancreatic buds.

5 The pancreatic islets of Langerhans are composed of four major cell types – alpha (A), beta (B), delta

(D), and pancreatic polypeptide (PP or F) cells which primarily secrete glucagon, insulin,

somatostatin, and PP, respectively.

6 The different types of islet cells are not evenly distributed throughout the pancreas leading to a

differential distribution of functional neuroendocrine tumors. In addition, resection of different parts

of the pancreas has differing endocrine effects.

7 Pancreatic endocrine secretion also regulates pancreatic exocrine secretion. Insulin stimulates

pancreatic exocrine secretion, amino acid transport, and synthesis of protein and enzymes, whereas

glucagon acts in a counter-regulatory fashion, inhibiting the same processes.

8 Tests of pancreatic exocrine function include the secretin test, 24-hour fecal fat determination,

dimethadione (DMO) test, the Lundh test meal, the triolein breath test, and the paraaminobenzoic

acid (PABA) test. These tests help differentiate steatorrhea due to pancreatic insufficiency from other

digestive disorders.

9 Exogenous administration of somatostatin inhibits the release of insulin, glucagon, growth hormone,

and pancreatic polypeptide.

10 Knowledge of the relationship of the pancreas to surrounding structures including the stomach,

duodenum, distal bile duct, hepatic arterial blood supply, splenic artery and vein, celiac axis,

superior mesenteric artery and vein, portal vein, spleen, adrenal glands, colon and kidneys is critical

in preventing injury to these structures during pancreatic surgery.

11 Resectability in pancreatic cancer in the absence of metastatic disease depends on the extent of

involvement of the tumor with the major vascular structures including the superior mesenteric

artery, superior mesenteric vein (SMV), portal vein, and celiac axis.

INTRODUCTION

1 The pancreas is a digestive organ with both exocrine and endocrine function. The exocrine pancreas

constitutes 80% of the pancreatic mass and comprises acinar and ductal cells.

2 Acinar cells synthesize and secrete over 20 enzymes into the complex pancreatic ductal network,

which then delivers them to the duodenum. The pancreatic secretions are alkaline and provide the

optimal environment for the enzymes to carry out their digestive function in the small intestine.

3 The pancreatic endocrine cells are organized in discrete groups throughout the pancreas, called

islets of Langerhans. The islets directly secrete hormones including insulin, glucagon, and somatostatin,

directly into the blood stream in endo crine fashion. The primary function of the endocrine pancreas is

regulation of body energy, primarily through control of carbohydrate metabolism. Pancreatic endocrine

hormones also play a critical role in the complex regulation of pancreatic secretion and digestion.

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The pancreas lies transversely in the retroperitoneum at the level of the second lumbar vertebrae.

Understanding of the embryology of the pancreas is critical for recognizing rare congenital anomalies,

understanding their significance, and treating them appropriately. In addition, when performing

pancreatic and other upper abdominal operations, it is critical to understand the close relationship of the

pancreas to adjacent organs (duodenum, stomach, spleen, transverse colon, bile duct, and left adrenal

gland) and major vessels (celiac axis, superior mesenteric artery, superior mesenteric vein (SMV),

splenic artery and vein, portal vein, inferior mesenteric vein, and vena cava). Knowledge of the normal

pancreatic exocrine and endocrine physiology provides insight into the pathologic processes and

subsequent treatments that can affect the normal function of the pancreas.

EMBRYOLOGY

Normal Pancreatic Embryology

The pancreas begins developing during the fifth week of gestation. Pancreatic development begins at

the junction of the foregut and midgut as two endodermal pancreatic buds, the dorsal bud and the

ventral bud. The dorsal and ventral buds comprise endoderm covered in splanchnic mesoderm. Both the

acinar and islet cells differentiate from the endodermal cells found in the embryonic buds while the

splanchnic mesoderm eventually develops into the dorsal and ventral mesentery.

The dorsal bud forms first and is larger. It ultimately forms much of the head, body, and tail of the

pancreas. As the duodenum grows and rotates, the ventral bud rotates clockwise (Fig. 52-1) and fuses

with the dorsal bud forming the uncinate process and inferior head of the pancreas. In the majority of

cases, the duct in the ventral bud fuses with the duct in the dorsal bud to become the main pancreatic

duct (duct of Wirsung), which drains the majority of the pancreas into the duodenum through the major

papilla, or ampulla of Vater. The proximal duct of the dorsal bud forms the lesser or minor pancreatic

duct (duct of Santorini) which drains into the duodenum through the minor papilla proximal to the

ampulla of Vater.

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