This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrine System, Subject name: Physiology
Which of the following organs is not involved in calcium homeostasis? 
Select and explain. 
A. Kidneys, B. Skin, C. Intestines, D. Lungs
D: Lungs
Answer: D: Lungs 
Explanation: Ca2+ homeostasis is achieved by 3 hormones: PTH, calcitonin, and vit. D. Ca2+ levels are regulated from 3 tissues: bone, intestine, and kidneys. Skin has the precursor for vit. D synthesis. Vitamin D is involved in Ca2+ absorption from G.I.T.