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: ENT
Inner ear contain endolymph and perilymph. Which of the following structure of the inner ear produces endolymph? 
Select and explain. 
A. Is a filtrate 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 entire membranous labyrinth and resembles intracellular fluid, being rich in K ions. It is secreted by the secretory cells of the stria vascularis of the cochlea and by the dark cells (present in the utricle and near the ampullated ends of semicircular ducts).