The pancreas is elongated next to the duodenum, and the normal pancreas weighs 50 to 75 grams. Pancreatic islets are endocrine tissues scattered in the pancreas, which are aggregated by cells of different sizes, distributed in an island shape between the acinar tissues that secrete pancreatic juice.
 
There are 1 million to 2 million pancreatic islets in the human pancreas, whose volume accounts for 1% to 2% of the entire pancreas and weighs 1 to 2 grams. There are four main cell types on the islets: B cells, A cells, D cells, and F cells, which secrete different hormones.
(1) B cells: mainly located in the body and tail of the pancreas, accounting for 60% to 80% of the islet cells, mainly secrete insulin, which lowers blood sugar.
(2) A cell: accounts for 15% to 20% of the islet cells and secretes glucagon, whose effect is exactly the opposite of that of insulin, which can increase blood sugar.
(3) D cells: 5% to 10% of the total number of islet cells, secreting growth hormone inhibitory hormone.
(4) F cells: accounting for 1.5% to 2.0% of the total number of islet cells, secreting pancreatic polypeptide.