Based on OCR A-level knowledge. Here I try to explain the process of insulin secretion as quickly and concisely as possible. This is based on the OCR scheme of work, and is designed to either get you started, or to help you revise.

Fastest explanation of beta cell function in the islets of Langerhans. This whole process takes place in the pancreas, which is an interesting organ, as it serves endocrine and exocrine functions.

Exocrine cells secrete proteins, usually enzymes, into ducts.
Endocrine cells secrete hormones directly into the blood.