The correct answer is C. Pancreas.
Islets of Langerhans are small clusters of cells in the pancreas that produce hormones that help to regulate blood sugar levels. They are named after Paul Langerhans, a German physician who first described them in 1869.
The islets of Langerhans are made up of four types of cells: alpha cells, beta cells, delta cells, and F cells. Alpha cells produce glucagon, a hormone that raises blood sugar levels. Beta cells produce insulin, a hormone that lowers blood sugar levels. Delta cells produce somatostatin, a hormone that regulates the release of other hormones. F cells produce pancreatic polypeptide, a hormone that helps to regulate digestion.
The islets of Langerhans are important for maintaining healthy blood sugar levels. When blood sugar levels rise, the beta cells in the islets of Langerhans release insulin. Insulin helps cells to take up glucose from the bloodstream, which lowers blood sugar levels. When blood sugar levels fall, the alpha cells in the islets of Langerhans release glucagon. Glucagon helps the liver to release glucose into the bloodstream, which raises blood sugar levels.
The islets of Langerhans are also important for regulating other aspects of metabolism, such as the metabolism of fats and proteins. They play a role in the regulation of appetite and weight.
Disorders of the islets of Langerhans can lead to a variety of health problems, including diabetes mellitus, hypoglycemia, and pancreatitis.