Pancreas

The pancreas is an elongated gland lying retroperitoneally behind the stomach, divided anatomically into a head (cradled by the duodenum), neck, body, and tail (reaching toward the spleen). It is unusual in serving two distinct systems at once: it is both a digestive organ and an endocrine gland.

The exocrine pancreas makes up the bulk of the organ. Its acinar cells produce digestive enzymes — amylase for carbohydrates, lipase for fats, and proteases such as trypsin for proteins — which travel through the pancreatic duct into the duodenum. Duct cells add bicarbonate-rich fluid that neutralizes acidic chyme arriving from the stomach, creating the pH digestive enzymes need to work.

The endocrine pancreas consists of the islets of Langerhans scattered through the gland. Beta cells secrete insulin, which lowers blood glucose by driving cellular uptake and storage; alpha cells secrete glucagon, which raises blood glucose by stimulating glycogen breakdown and gluconeogenesis; and delta cells secrete somatostatin, which inhibits both. This hormonal push-pull keeps blood glucose within a narrow range, and its failure underlies diabetes mellitus. Major pancreatic disorders include acute and chronic pancreatitis — often from gallstones or alcohol — and pancreatic cancer, which most commonly arises in the head of the gland.

The pancreas is tested across health exams: the USMLE Step 1 covers its anatomy and disorders, the MCAT tests its digestive and hormonal roles in the context of metabolism, and the CCMA exam covers it among the accessory organs of the gastrointestinal tract.