This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Most metabolically active layer in the bone is: 
Select and explain. 
A. Periosteum, B. Endosteum, C. Cancellous bone, D. Coical bone
B: Endosteum
Answer: B: Endosteum 
Explanation: Ans: B. Endosteum (Ref Osteoporosis and Bone Densitomeny Measurements edited by Giuseppe Guglielmi/ p72)The most metabolically active component of bone is the endosteal surface of coex with trabecula bone being next most common active area .Metabolically active layer in bone:Are in immediate contact with bone marrowEndosteum of coex - Most active layer in bone (overall).Total area of endosteal surface approximately 0.5 m2.Higher remodelling activity than periosteal surface -Due to greater biomechanical strain or greater cytokine exposure from adjacent hone marrow compament.Order:Trabecular bone - Next most metabolically active area.In children = Periosteum is very active.