This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ear, Subject name: ENT
Endolymph in the inner ear 
Select and explain. 
A. Is a filterate of blood serum, B. Is secreted by Stria vascularis, C. Is secreted by Basilar membrane, D. Is secreted by Hair cells
B: Is secreted by Stria vascularis
Answer: B: Is secreted by Stria vascularis 
Explanation: Endolymph fills the membranous labyrinth and rich in K ions and is secreted by stria vascularis and the dark cells present in the utricle and near the ampullated end of semicircular ducts. Reference Dhingra 6th edition pg-24.