The islets of Langerhans make up the endocrine portion of pancreas. They are constellations of specialized cells which secrete important hormones that regulate glucose levels in the bloodstream and metabolism. They were named after the German scientist Paul Langerhans who discovered and carefully studied them between 1869 and 1871.
Description
Each one of the islets is a mass or assemblage of endocrine cells, measuring between 50 to 500 microns in diameter. There are between 12 and 20 islets per milligram of gland tissue. In human beings and the rest of primates, they are basically composed of four types of endocrine cells; α (alpha), β (beta), δ (delta), and ε (epsilon) cells.
Alpha cells secrete glucagon. The function of glucagon is extremely important to avoid hypoglycemia, keeping sugar levels up. It induces the liver to tap the body reservoirs of fuel (glycogen and fat). This hormone is what makes you burn fat when you work out or when you are fasting. People who suffer from type I diabetes, their pancreas does not secrete glucagon and insulin.
Beta cells produce insulin, which makes the liver lower the excess glucose (sugar) in the bloodstream, converting it into glycogen, the first fuel reserve. If the sugar keeps going up, the liver cell mitochondria metabolize it into triglyceride molecules that end up in the adipose cells. This is how you become overweight. Excess insulin is deleterious (bad) over the years; thus you have to reduce your carbs consumption.
Delta cells secrete and release somatostatin, which is also produced by the hypothalamus. It inhibits the secretions of hormones, such as insulin, glucagon, somatotropin (growth hormone), and thyroid stimulating hormone.
Epsilon cells produce grhelin, which triggers hunger. It is also released by the stomach.
