pancreas final 2015 - medscistudents 1102/12. pancreas...•...
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PANCREAS
Ini$a$on of dorsal and ventral pancrea$c buds at approximately 30 days pos9er$liza$on. Note that the buds appear from opposite sides of the gut tube and that the ventral bud arises from a common outgrowth that will form the liver and gall bladder. (B) A slightly later stage in pancreas development showing the ventral bud moving posteriorly to join the dorsal bud. Endoderm from the gut tube forms the parenchyma of the pancreas, gall bladder, and liver; whereas surrounding mesoderm forms the connec$ve $ssue.
As the two buds increase in size, the ventral bud moves into closer proximity to its dorsal counterpart. By week 6, the two buds fuse and the duct connec$ng the dorsal bud to the foregut usually degenerates.
Pancreas development at week 6 of development showing fusion of the dorsal and ventral buds. The main duct is derived from the distal part of the dorsal bud and the proximal part of the ventral. In 10% of cases, the en$re dorsal duct remains to form an accessory pancrea$c duct.
Pancreas
• A soN lobulated gland, consis$ng of both exocrine and endocrine parts and very liOle connec$ve $ssue. It extends to the leN and slightly upwards across the posterior abdominal wall from the concavity of the diaphragm to the hilum of the spleen. The pancreas lies behind the stomach, separated by the cavity of the lesser sac.
• Anatomy The pancreas lies behind the peritoneum of the posterior abdominal wall and is oblique in its orienta$on. The head of the pancreas is on the right side and lies within the “C” curve of the duodenum at the second vertebral level (L2). The $p of the pancreas extends across the abdominal cavity almost to the spleen. Collec$ng ducts empty diges$ve juices into the pancrea$c duct, which runs from the head to the tail of the organ. The pancrea$c duct emp$es into the duodenum at the duodenal papilla, alongside the common bile duct
• It occupies the posterior part of the epigastrium and the leN hypochondrium
• Its length varies from 12.5 to 15 cm., and its weight from 60 to 100 gm.
• The pancreas may be divided into five major regions—the head, neck, body, tail and uncinate process. The distal end of the common bile duct can be found behind the upper border of the head of the pancreas. This duct courses the posterior aspect of the pancrea$c head before passing through the head to reach the ampulla of Vater (major papilla). The uncinate process is the segment of pancrea$c $ssue that extends from the posterior of the head. The neck of the pancreas, a part of the gland 3–4 cm wide, joins the head and body. The pancrea$c body lies against the aorta and posterior parietes, and anteriorly contacts the antrum of the stomach
• Junc=on between head and neck in front separated by the groove for the gastroduodenal artery and behind by the right margin of the groove for the portal vein
• Junc=on between the neck and body In front not possible to separate behind separated by the leN margin of the portal groove
• Junc=on between the body and tail in front not dis$nguishable behind separated by the junc$on of peritoneal and non peritoneal areas.
Head of Pancreas
• two surfaces, anterior and posterior • four borders: upper, lower, right, leN • One process known as the uncinate process
Anterior Surface • It is directed forward and laterally and is separated from the neck in the upper and leN part by a groove for the gastroduodenal artery
• Rela=ons: • Upper part is non peritoneal and is related to the transverse colon
• Lower part is covered with peritoneum which is derived from the inferior layer of transverse meso colon and is related to the coils of the jejunum
• Superior mesenteric vessels in front of the uncinate process
Head
• Posterior Surface is non-‐peritoneal and is directed backwards and medially
• Rela=ons • inferior vena cava, the common bile duct, both renal veins, • the right crus of the diaphragm with the following structures
– The right middle supra-‐renal, renal and gonadal arteries – Right coeliac ganglion
Separated by the IVC the following structures are situated behind the head
Right sympathe$c trunk and right psoas major
Head Borders • The Head of Pancreas (caput pancrea$s) is flaOened from before backward, and is lodged within the curve of the duodenum. Its upper border is overlapped by the 1st part of the duodenum and its lower overlaps the horizontal part; its right and leN borders overlap in front, and insinuate themselves behind, the descending and ascending parts of the duodenum respec$vely.
• In the groove between the pancreas and duodenum lodge the ventral and dorsal anastomoses of superior and inferior pancrea$coduodenal vessels.
Uncinate process
• Triangular projec$on which arises from the lower and leN part of the head. It passes upwards and medially behind the superior mesenteric vessels and lies on a more posterior plane than the rest of the gland
• Anterior: superior mesenteric vessels the vein lies on the right side of the artery.
• Posterior: abdominal aorta • Above leN renal vein
NECK
• It connects the head with the body and is about 2cm long. It juts forwards, upwards and to the leN, because at the neck the plane of the head and that of the body meet at a forward angle.
NECK • Anterior surface is covered with peritoneum of the the lesser
sac and is related to the pylorus of the stomach • Posterior surface is non-‐peritoneal and presents a shallow
groove which contains the the superior mesenteric vein in its lower part and the trunk of the portal vein in the upper part.
• Upper border is overlapped by the 1st part of the duodenum • Lower border gives aOachment to the root of the transverse
mesocolon.
BODY
• It is prismoid in appearance, triangular on cross sec$on and extends from the front of the aorta to the front of the leN kidney.
• Has three surfaces and three borders
BODY
• The anterior surface of pancreas is somewhat concave; and is directed forward and is covered by peritoneum of the lesser sac which is derived from the mesocolon:
• Rela$ons • Postero-‐inferior surface of stomach separated by lesser sac (stomach bed)
BODY
• The posterior surface of the body is devoid of peritoneum, and presents the following rela$ons:
• abdominal aorta with the origin of the superior mesenteric artery , • leN crus of the diaphragm • LeN psoas and sympathe$c trunk • leN kidney across its hilum • leN supra-‐renal gland,, • LeN renal vessels and pelvis of the leN ureter • LeN supra-‐renal and leN gonadal vessels
• Splenic vein the above men$oned structures are separated from the pancreas by the splenic vein, which runs in a groove from leN to right and receives the inferior mesenteric vein.
BODY
• The inferior surface is narrow on the right but broader on the leN, and is covered by peritoneum; it lies upon the duodenojejunal flexure and on some coils of the jejunum; its leN extremity rests on the leN colic flexure.
Body
• Superior border • Close to the right end it presents a conical projec$on known as the tuber omental.
• Celiac artery is related above the tuber and the hepa$c artery runs along the right side of the tuber. Rest of the border on the leN side of the tuber omental is accompanied with the tortuous splenic artery.
Body
• Anterior border it separates anterior from inferior surfaces and gives aOachment to the root of transverse mesocolon where layers diverge Inferior border
Superior mesenteric vessels emerge under cover of the right end of this border
TAIL • It is the narrow leN end of the gland, passes between the layers of the lieno-‐renal ligament and reaches the spleen. Tail is the most mobile part of the gland and lies at a higher level than the head, opposite the lower border of T12 vertebra.
• Rela$ons • Anterior: stomach separated by the lesser sac • Posterior: spleen and splenic vessels • Inferior: leN colic flexure
• The Duct of Wirsung is the main pancrea$c duct extending from the tail of the organ to the major duodenal papilla or Ampulla of Vater . The widest part of the duct is in the head of the pancreas (4 mm), tapering to 2 mm at the tail in adults. The duct of Wirsung is close, and almost parallel, to the distal common bile duct before combining to form a common duct channel prior to approaching the duodenum. In approximately 70% of people, an accessory pancrea$c duct of Santorini (dorsal pancrea$c duct) is present. This duct may communicate with the main pancrea$c duct. The degree of communica$on of the dorsal and ventral duct varies from pa$ent to pa$ent.
• Smooth circular muscle surrounding the end of the common bile duct (biliary sphincter) and main pancrea$c duct (pancrea$c sphincter) fuses at the level of the ampulla of Vater and is called the sphincter of Oddi.
• This musculature is embryologically, anatomically, and physiologically different from the surrounding smooth musculature of the duodenum. The normal appearance through the endoscope includes the major and minor papilla. The major papilla extends 1 cm into the duodenum with an orifice diameter of 1 mm. The minor papilla is 20–30 mm proximal and medial. Its orifice is $ny and may be difficult to iden$fy.
Func$on of tehsphincter of Oddi; A, relaxed; B, contracted