General Flashcards
Anatomy
The pancreas is a soft, elongated, flattened gland that is 12 to 20 cm in length.
The adult gland weighs between 70 and 110 g.
The pancreas is coarsely lobulated and covered with fine connective tissue, without a true capsule.
It is primarily retroperitoneal, lying approximately at the level of the L1-L2 lumbar vertebrae.
Anterior and Posterior
The anterior surface of the head of the pancreas is adjacent to the pylorus, the first part of the duodenum, and the transverse colon.
The posterior surface abuts the hilum and medial border of the right kidney, the inferior vena cava and the right renal vessels, the right gonadal vein, and the right crus of the diaphragm.
neck of the pancreas
is a constricted part of the gland, extending from the head of the pancreas toward the left to connect the head with the body of the pancreas
1.5 to 2 cm long and 3 to 4 cm wide.
The body of the pancreas runs toward the left side, anterior to the aorta.
It is retroperitoneal and held against the aorta by the peritoneum of the lesser sac.
The anterior surface of the body is covered by peritoneum of the omental bursa, which separates the stomach from the pancreas.
The tail is relatively mobile, with its tip usually reaching the hilum of the spleen.
The tip of the tail is intraperitoneal lying between layers of the splenorenal ligament.
Ductal Structures
The main pancreatic duct (of Wirsung) begins near the tail of the pancreas.
The main duct turns caudal and posterior on reaching the head of the pancreas.
The duct of Wirsung and the common bile duct empty into the duodenum obliquely via the major papilla.
Three circular muscle bundles are called
sphincter of Oddi, act as sphincters encircling each duct as well as the ampulla of Vater.
Approximately 70% of the general population has a patent accessory duct (of Santorini),
minor duct
It is widest at the head of the pancreas, and the duct gradually tapers as it progresses to the tail.
Main pancreatic duct
Pancreatic duct diameter
Upper limits of normal for the pancreatic duct diameter in the head (5 mm), body (4 mm), and tail (3 mm)
Blood supply
rich circulation that is derived from branches of the celiac and superior mesenteric arteries.
head of the pancreas and surrounding duodenum
supplied by 2 pancreaticoduodenal arterial arcades.
They are formed by the anterior and posterior superior pancreaticoduodenal arteries from the hepatic branch of the celiac artery that join a second pair of anterior and posterior inferior pancreaticoduodenal arteries branching from the superior mesenteric artery.
The portal vein lies behind the pancreas and in front of the inferior vena cava.
common bile duct lies anterior to the portal vein with the hepatic artery to the left of the common bile duct.
HISTOLOGY AND ULTRASTRUCTURE
compound, finely nodular gland that in its contour bears some resemblance to the salivary glands.
basic subunit of the exocrine portion is the acinus, which is at its base a spherical mass of dark-staining secretory cells
acinar cells
spherical acinus connects to a goblet-shaped neck that is composed of tubular cells
duct cells
Histology
pancreatic ductal system is nonstriated and is lined by columnar epithelium. Goblet cells and occasional argentaffin cells are also present.
acinar cells
By light microscopy, acinar cells are tall pyramidal or columnar epithelial cells, with their broad bases on a basal lamina and their apices converging on a central lumen.
5 major cell types in the endocrine pancreas
Beta cells PP cells, also known as F cells Alpha cells make up 5% to 20% and secrete glucagon. Delta cells epsilon cells
Beta cells
most numerous, constituting about 50% to 80% of the islets.
secrete insulin and amylin.
PP cells
also known as F cells, make up 10% to 35% and secrete pancreatic polypeptide and adrenomedullin.
Alpha cells
make up 5% to 20% and secrete glucagon.
delta cells
The remaining 5% consists, secrete somatostatin,
epsilon cells
which secrete ghrelin
Embryonic and Fetal Development
arises from posterior foregut endoderm.
The dorsal pancreas forms the tail, body, and superior portion of the pancreatic head.
It also contains the dorsal duct that forms the distal portion of the main pancreatic duct (of Wirsung) and the entire minor accessory duct (of Santorini)
pancreas divisum
the accessory duct functions as the main conduit for drainage of pancreatic juice.
annular pancreas
Failure of the ventral pancreas to fully rotate around the duodenum, or persistence of the left ventral bud
primary transition
conversion of predifferentiated cells to a protodifferentiated state in which low levels of pancreas-specific proteins are present.
second phase, or the secondary transition
dramatic rise in pancreatic cell number and pancreas-specific protein synthesis, as well as an acceleration in both exocrine and endocrine differentiation.
Annular Pancreas
congenital anomaly in which a portion of the pancreas forms a thin band around the preampullary portion of the duodenum, leading to complete or partial bowel obstruction
more common in patients with other congenital anomalies such as trisomy 21, cardiac defects, malrotation, duodenal atresia, genitourinary anomalies, and tra- cheoesophageal fistula.
annular pancreas treatment of choice in children and in some adult patients.
Duodenoduodenostomy appears to be an effective surgical treatment for bowel obstruction in these cases
Complex pancreatic surgery is more likely to be required in adults compared with children.
Pancreas Divisum
results from a failure of the dorsal and ventral pancreatic ducts to fuse during embryogenesis
3 types of pancreas divisum
Classic or complete divisum
dominant type or dorsal duct pancreas divisum
incomplete pancreas divisum
diagnosed by endoscopic retrograde pancreatography, EUS, abdominal CT, or MRCP
Classic or complete divisum
complete failure of fusion between the dorsal duct (Santorini) and ventral duct (Wirsung), occurs in 71% of patients with PD.
dominant type or dorsal duct pancreas divisum
absence of the ventral duct, occurs in 6% of patients with divisum.
incomplete pancreas divisum
remains a small communication between the ventral and dorsal ducts, occurs in 23% of patients.
gold standard in diagnosing PD
Although endoscopic retrograde pancreatography
pancreatic rest, occurs in 0.6% to 13.7% of the population according to autopsy material
This tissue lacks a physical connection to the pancreas and has an independent blood supply.
smooth, broad-based submucosal mass with about 45% having a classic central umbilication.
Ectopic Pancreatic Tissue
Pancreatic rests are most commonly found
stomach, duodenum, proximal jejunum, and ileum.
used for accurate preoperative differentiation between GISTs and pancreatic rests
eus
typical features on EUS of ectopic pancreatic tissue
antral location, mucosal dimple, 3 to 4 layers, and lesional duct.
endoscopic band ligation with snare polypectomy
agenesis of the dorsal pancreas has been associated with polysplenia and intestinal malrota- tion,renal anomalies,and heterotaxy
congenital short pancreas
Pancreaticobiliary malunion
Long common channels or pancreaticobiliary malunion can predispose to pancreatitis or biliary cancer.
