Embryological Development

In order to understand the anatomical variations and congenital anomalies of the pancreas, many of which have practical surgical implications, it is important to realize that this organ originates from two separate embryonic anlagen: a ventral and a dorsal primordium. On or about the 24th day of gestation, the diverticulum begins to bud from the ventral surface of that part of the primitive digestive tube which is destined to later become the duodenum. This hepatic anlage invades the ventral mesentery and later develops into the liver, bile ducts, and gallbladder. Some two days later (26th day of gestation), a similar diverticulum emanates from the dorsal surface of the digestive tube. In normal pancreatic development, the pancreas arises from the dorsal and ventral anlagen in the 4-week embryo (fig. 1). The ventral anlage consists of two buds, a right and left lobe, and they arise on each side of the common bile duct, as described by Odgers [5]. The left lobe of the ventral pancreatic anlage disappears rapidly. This develops into the dorsal anlage of the pancreas, growing rapidly within the dorsal mesentery. The smaller ventral pancreatic anlage buds a little later from the hepatic diverticulum on the 32nd day (fig. 2) [7].

A series of rapid development changes (elongation of the hepatic anlage to from the bile duct, disappearance of the ventral mesentery, rapid growth of the left wall of the duodenum) leads to a rotation of the common bile duct, together with the ventral pancreatic anlage, into a dorsal position behind the primitive superior mesenteric vessels.

Thus, the dorsal and ventral portions of the pancreas come into close contact by the 37th day of gestation. While these two portions and their drawing ducts begin to amalgamate, the right leaf of the dorsal mesentery fuses with the posterior abdominal wall, thus determining the retroperitoneal position of the pancreas and three-quarters of the duodenum. This avascular plane, the fascia of Treitz, separates the posterior aspect of the pancreas from the abdominal

Fig. 1. Fifth-week embryo. Both a ventral and dorsal pancreatic anlage were observed. The dorsal pancreatic anlage was already lobed. HE. CBD = Common bile duct; SMV = superior mesenteric artery.
Superior Mesenteric Artery Development

Fig. 2. Sixth-week embryo. Both the ventral and dorsal pancreatic anlage were lobed and partially fused. A series of rapid development changes leads to a rotation of the common bile duct, together with the ventral pancreatic anlae, into a dorsal position behind the primitive superior mesenteric vessels. HE. CBD = Common bile duct; SMV = superior mesen-teric artery.

Fig. 2. Sixth-week embryo. Both the ventral and dorsal pancreatic anlage were lobed and partially fused. A series of rapid development changes leads to a rotation of the common bile duct, together with the ventral pancreatic anlae, into a dorsal position behind the primitive superior mesenteric vessels. HE. CBD = Common bile duct; SMV = superior mesen-teric artery.

wall. It is this plane that facilitates the mobilization maneuver described by Kocher.

By the end of the 7th week of gestation, with the embryo only about 13 mm long, gross morphological development of the pancreas is largely complete. The ventral anlage now comprises the uncinate process and most of the pancreatic head. Its duct (the duct of Wirsung) fuses with the duct of the dorsal anlage and drains into the duodenum together with the common bile duct.

The dorsal anlage constitutes the body and tail of the pancreas and the cranial part of the head. The distal part of its duct joins that draining the ventral anlage, although its proximal portion (the duct of Santorini) either drains into the duodenum through a minor papilla or drains retrogradely into the the duct of Wirsung; in some cases it degenerates completely.

The functional development of the pancreas into an exocrine and endocrine gland occurs much later. Secretory acini first appear at the ends of ducts in the third gestational month. Trypsin is formed at about 22 weeks, but full exocrine function is not achieved until six months after birth [8].

Primary islet cells, which probably originate from the neural crest (as do other cells of the APUD system) appear in the 8th week, but are gradually replaced by secondary islets from the third gestational month onwards. Insulin may be detected from the end of the third month, but full endocrine function is not established until after birth.

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Getting Back Into Shape After The Pregnancy

Getting Back Into Shape After The Pregnancy

Once your pregnancy is over and done with, your baby is happily in your arms, and youre headed back home from the hospital, youll begin to realize that things have only just begun. Over the next few days, weeks, and months, youre going to increasingly notice that your entire life has changed in more ways than you could ever imagine.

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