Question

Which part of the pancreas produces and secretes insulin?

Answer 1

Hint: The pancreas is a glandular organ which is considered as a heterocrine gland because it contains both endocrine and exocrine glandular tissue. The exocrine tissue makes up about $99\mathrm{\%}$ of the pancreas by weight whereas the endocrine tissue makes up the other $1\mathrm{\%}$. The endocrine portion of the pancreas consist of small bundles of the cells, called islets of Langerhans which produce insulin.

Complete answer:
The islets of Langerhans are responsible for the pancreatic endocrine function and each islet mainly contains 3 types of cell; alpha cells, beta cells and delta cells which are responsible for the secretion of pancreatic hormones.
 Among them beta cells of islets of Langerhans produce the hormone insulin, which lowers blood glucose levels. Alpha cells and delta cells produce glucagon (which raises blood glucose levels) and somatostatin (Regulate the secretion of insulin and glucagon).
The hormone glucagon or somatotropin triggers the release of insulin from the beta cell but glucose is the most important stimulator for release of insulin. When the glucose level is increased in the bloodstream, insulin is released to counter it. The inability of the islet cells of pancreas to produce insulin or the failure to produce sufficient amounts of insulin to control blood glucose level are the causes of diabetes mellitus.

Note:
The exocrine portion of the pancreas plays an important role in food digestion. Insulin is an important hormone, to lower the blood glucose levels; promote the glucose metabolism; prevents the release of glucose by liver and inhibits the breakdown and release of fats.