What structure secretes calcitonin in lizards?

Calcitonin is a hormone critical for regulating calcium levels in the blood, and in lizards, it is secreted specifically by the ultimobranchial bodies. These structures are derived from the branchial (or gill) arches during embryonic development and play a significant role in calcium metabolism.

In reptiles, including lizards, the ultimobranchial bodies are situated in the neck region and are associated with the thyroid gland, but they have a distinct function. The secretion of calcitonin from these bodies helps to lower blood calcium levels by inhibiting osteoclast activity in the bones and promoting calcium excretion in the kidneys. This action is important for maintaining overall calcium homeostasis, particularly in environments where dietary calcium may fluctuate.

In contrast, while the thyroid gland is responsible for secreting other hormones, such as thyroxine, it does not secrete calcitonin in lizards. The adrenal cortex and pineal gland have different roles entirely, focusing on stress responses and circadian rhythm regulation, respectively. Therefore, the ultimobranchial bodies are recognized as the primary source of calcitonin in lizards, marking their critical role in calcium regulation within these reptiles.