Left and right hepatic ducts, 4. Right and left lobes of liver. The pancreas is an body parts English for kids with transcription and digestive organ that, in humans, lies in the upper left part of the abdomen.
It is found behind the stomach. Anatomically, the pancreas is divided into the head of pancreas, the neck of pancreas, the body of pancreas, and the tail of pancreas. The head is surrounded by the duodenum in its concavity. The endocrine part is composed of hormonal tissue distributed along the pancreas in discrete units called islets of Langerhans. The upper margin of the pancreas is blunt and flat to the right, and narrow and sharp to the left, near the tail. It begins on the right in the omental tuber, and is in relation with the celiac artery, from which the hepatic artery courses to the right just above the gland, while the splenic artery runs toward the left in a groove along this border. The anterior surface of the pancreas faces the front of the abdomen.
Most of the right half of this surface is in contact with the transverse colon, with only areolar tissue intervening. From its upper part, it joins to the neck of the pancreas at a well-marked prominence, the omental tuber, which abuts the lesser omentum. Its right edge is marked by a groove for the gastroduodenal artery. The lower part of the right half, below the transverse colon, is covered by peritoneum continuous with the inferior layer of the transverse mesocolon, and is in contact with the coils of the small intestine. The pancreas receives blood from branches of both the coeliac artery and superior mesenteric artery. The pancreas contains tissue with an endocrine and exocrine role, and this division is also visible when the pancreas is viewed under a microscope. Darker-staining cells form clusters called acini, which are arranged in lobes separated by a thin fibrous barrier.
The secretory cells of each acinus surround a small intercalated duct. The size of the pancreas varies considerably. Several anatomical variations exist, relating to the embryological development of the two pancreatic buds. The pancreas develops from these buds on either side of the duodenum. An accessory pancreatic duct may exist if the main duct of the pancreas does not regress. Schematic illustrating the development of the pancreas from a dorsal and a ventral bud. An additional ventral lobe that usually regresses during development is omitted.
As part of embryonic development, the pancreas forms from the embryonic foregut and is therefore of endodermal origin. Pancreatic development begins with the formation of a ventral and a dorsal pancreatic bud. Differential rotation and fusion of the ventral and dorsal pancreatic buds results in the formation of the definitive pancreas. As the duodenum rotates to the right, it carries with it the ventral pancreatic bud and common bile duct. Differentiation of cells of the pancreas proceeds through two different pathways, corresponding to the dual endocrine and exocrine functions of the pancreas.
The multi-potent pancreatic progenitor cells have the capacity to differentiate into any of the pancreatic cells: acinar cells, endocrine cells, and ductal cells. These progenitor cells are characterised by the co-expression of the transcription factors PDX1 and NKX6-1. Insulin and glucagon can be detected in the human fetal circulation by the fourth or fifth month of fetal development. Blood glucose levels are maintained at a constant level in the body by a negative feedback mechanism. When the blood glucose level is too high, the pancreas secretes insulin and when the level is too low, the pancreas then secretes glucagon.
The flat line shown represents the homeostatic set point. The sinusoidal line represents the blood glucose level. Approximately 3 million cell clusters called pancreatic islets are present in the pancreas. Within these islets are four main types of cells which are involved in the regulation of blood glucose levels. The islets are crisscrossed by a dense network of capillaries. The capillaries of the islets are lined by layers of islet cells, and most endocrine cells are in direct contact with blood vessels, either by cytoplasmic processes or by direct apposition. The islets function independently from the digestive role played by the majority of pancreatic cells.