Endocrine gland and exocrine gland

A gland is a group of cells that come together to make something and release it. The question that separates the two families is simple: does it release it into a tube, or into the blood?

An exocrine gland releases it into a tube. Its secretion travels through a system of ducts and ends up coming out onto an epithelial surface, which is the lining of some part of the body: the skin, the inside of the intestine, the mouth. An endocrine gland has no such tube: it puts its product directly into the bloodstream, and the blood distributes it.

On the exocrine side, the secretion starts in the acinus, the cluster of cells where each duct begins, and it leaves the cell by three different mechanisms, each with its own name: merocrine, apocrine and holocrine. How they differ from one another is the subject of another card.

And there is one organ that does both at the same time, the pancreas. Its exocrine part makes a juice loaded with bicarbonate that helps neutralize the acid coming from the stomach. Its endocrine part, by contrast, sends its product straight into the blood.