This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General, Subject name: Orthopaedics
Osteoclasts have all of the following except - 
Select and explain. 
A. Bone resorption, B. Receptor for parathormone, C. Ruffled border, D. Rank ligand
B: Receptor for parathormone
Answer: B: Receptor for parathormone 
Explanation: Ans. is 'b' i.e., Receptor for parathormone o Osteoclasts are found in sites in which bone is being remodeled. These are multinucleated giant cells and formed by fusion of mononuclear cells (monocytes & macrophages). These cells are the principal mediator of bone resorption.The characteristic feature is the area of infolded plasma membrane known as ruffled border which is surrounded by an organelle free clear zone through which osteoclast attaches to bone & which is the site of bone resorption.# Though osteoclasts are responsible for resorption, they act when they are activated through osteoblasts# This is because, receptors for hormone that stimulate resorption (parathormone) are present on osteoblasts (not on osteoclasts).# Parathormone activates osteoblasts which then secrete mediators of osteoclastogenesis that stimulate osteoclasts for bone resorption.# RANK binds to RANK Ligand which stimulates bone resorption.