This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anatomy of Bone & Fracture Healing, Subject name: Orthopaedics
The bone matrix has the following crystals - 
Select and explain. 
A. Calcium hydroxyapatite, B. Calcium pyrophosphate, C. Calcium phosphate, D. Calcium sulphate
A: Calcium hydroxyapatite
Answer: A: Calcium hydroxyapatite 
Explanation: Ans. is 'a' i.e., Calcium hydroxyapatiteStructure of boneo Bone is a specialized connective tissue.o Bone components areInorganic elements (65%)Organic matrix (35%)1. Inorganic elementsIt is the mineral phase, principally composed of calcium and phosphate, mostly in the form of hydroxyapatite ,2. Organic maxtixOrganic matrix consists of cells of bones and protein of matrix. This unminerilized matrix is called osteoid, i.e. unminerilized bone is known as oteoid. Osteoid with mineral (i.e. mineralized osteoid) is complete bone.Protein of matrixo It is mainly formed by type I collagen and a family of noncollagenous proteins like osteocalcin and osteonectin that are derived mainly from osteoblasts.Cells of matrixo The cells of bone areOsteoblastsOsteoclastsOsteocytes