Describe the structure of the mucosa that lines the respiratory tract and thr structural changes observed along its length from bronchi to alvsoli (ie. why does it transition from pseudostratified ciliated columnar epithelium to simple squamous). Calcium is primarily responsible for supporting bone health, as well as: A. Oxygen transport B. Muscle contraction and nerve function C. Fighting the effects of free radicals D. Digestion 38. Osteoporosis can develop due to a: A. Lack of testosterone and calcium B. Overabundance of estrogen, calcium, and vitamin D C. Lack of estrogen and vitamin C D. Lack of estrogen, calcium, and vitamin D