Chief cells spend most time inactive due to normal calcium level conditions. These inactive cells are classified as cuboidal. They have low levels of secretory granules, as opposed to active chief cells. These granules can contain acid phosphatase. Acid phosphatase is only found in larger secretory granules, 400 to 900 nm in diameter, and is less prevalent in smaller granules. This acid phosphatase is also present in the Golgi apparatus of the chief cell. However, the Golgi apparatus areas associated with parathyroid hormone packaging contained little or no acid phosphatase. The chief cells become active in response to low calcium in the blood. The low level is sensed by the calcium- sensing receptor. These active cells have a greater electron density than the inactive chief cells. The electron density is caused by the secretory granules. The chief cell is thought to have a clear cytoplasm.