This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nutrition and Metabolic disorders,Systemic conditions ,Genodermatoses, Connective tissue disorders,Photodermatoses, Subject name: Dental
[{'content': 'Vitamin D is synthesized by? \nSelect and explain. \nA. Keratinocytes, B. Granular cells, C. Melanocytes, D. Prickle cells', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The keratinocytes of the skin are unique in being not only the primary source of vitamin D for the body, but in possessing the enzymatic machinery to metabolize vitamin D to its active metabolite 1,25 dihydroxy vitamin D. Fuhermore, these cells also express the vitamin D receptor (VDR) that enables them to respond to the 1,25(OH)2D they produce.', 'role': 'assistant'}]