Adrenal gland histology

The adrenal gland isn't one uniform lump: it's built in layers, like a piece of fruit that shows skin, flesh, and pit when you cut it open. The outer part is called the cortex, and in an adult the cortex has three zones arranged from the outside in. The first, the most superficial, is the glomerulosa. Below it comes the fasciculata. And deeper still, right up against the center, is the reticularis. That order is always the same, which is why it works as a landmark when you're looking at the inside of the gland.

The center of the gland is taken up by something different, called the medulla. That's where the cells live that release catecholamines, substances the gland sends out into the blood. So a single gland holds two territories: the outer ring with its three zones, and the core in the middle with its catecholamine-secreting cells.