Final answer:
Calcitonin, produced by the thyroid gland, helps regulate calcium levels by inhibiting osteoclast activity, stimulating osteoblasts, and promoting renal excretion of calcium. Its role in humans, although not as significant as in some species, is still important, especially in certain life stages.
Step-by-step explanation:
The statement that calcitonin counteracts the actions of thyroid-stimulating hormone (TSH) in some species but lacks a major physiological action in humans is false. Calcitonin, which is produced by the parafollicular cells of the thyroid gland, plays a role in regulating calcium concentrations in the body. It acts by inhibiting osteoclast activity, which in turn decreases bone resorption and lowers blood calcium levels. Additionally, it promotes the activity of osteoblasts, thereby facilitating calcium deposition in bones, and increases the excretion of calcium by the kidneys. While the role of calcitonin in humans is not as significant as in some other species, it still contributes to maintaining calcium homeostasis, particularly during stages like childhood, pregnancy, and periods of prolonged starvation.