KEY Adv, adventitia AT, adipose tissue BV, blood vessel CT, connective tissue, lamina propria Ep, epithelium RAS, Rokitansky-Aschoff sinus L, lymphocytes MC, mucous cells Muc, mucosa Mus, muscularis PC, plasma cells SM, smooth muscle arrows: Top left fgure, recess in luminal surface; Top right figure, intercellular spaces
The pancreas is an elongated extramural digestive gland with a head nestled in the C-shaped bend of the duodenum, a body that crosses the midline of the abdomen, and a tail extending across the back of the abdomen. It is a mixed gland containing both an exocrine component and an endocrine component that have distinctive characteristics. The exocrine component is a compound tubuloacinar gland with a branching network of ducts that convey the exocrine secretions to the duodenum. These secretions consist primarily of inactive forms of potent prote-olytic enzymes, as well as amylase, lipase, nucleases, and electrolytes, particularly HCO3 . The endocrine component is isolated as highly vascularized islets of epithelioid tissue (islets of Langerhans). The islet cells secrete a va-riety of polypeptide and protein hormones, most notably insulin and glucagon, which regulate glucose metabolism throughout the other tis-sues of the body. Other hormones secreted by islet cells include somatostatin, pancreatic polypeptide, vasoactive intestinal peptide, secretin, motilin, and substance P. All of these substances, with the exception of insulin, are also secreted by the population of enteroendocrine cells in the intestine, the organ from which the pancreas is derived during embryonic development. While insulin and glucagon act primarily in en-docrine regulation of distant cells, the other hormones (and glucagon) have significant roles in the paracrine regulation of the insulin-secreting B cells of the pancreatic islet.
Pancreas, human, H&E ×160; inset ×360.
The pancreas is surrounded by a delicate capsule of moderately dense connective tissue. Septa from the capsule divide the pancreas into lobules, one of which is shown here, bounded by connective tissue (CT). Larger blood vessels (BV ) travel in the connective tissue septa; nerves also travel in the septa, but they are seen infrequently. Within the lobule are the numerous acini of the exocrine component, an intralobular duct (InD), intercalated ducts (not readily evident at this low magnification), and islets of Langerhans (IL). Also within the lobule are the small blood vessels and the connective tissue serving as a stroma for the parenchymal elements of the gland.
Pancreas, human, H&E ×600.
Acini of the pancreas consist of serous cells. In sections, the acini present circular and irregular profiles. The lumen of the acinus is small, and only in fortuitous sections through an acinus is the lumen included (asterisks). The nucleus is characteristically in the base of the acinar cell. There is a region of intense basophilia adjacent to the nucleus. This is the ergastoplasm (Er), and it reflects the presence of rER that is active in the synthesis of pancreatic enzymes. Some acini reveal a centrally positioned cell with cytoplasm that shows no special staining characteristics in H&E–stained paraffin sections. These are centroacinar cells (CC). They are the beginning of the intercalated ducts.
This figure demonstrates particularly well the morphology and relationships of the intercalated ducts. Note, first, the cross-sectioned intralobular duct (InD) consisting of cuboidal epithelium. (There are no striated