Which describes stereocilia?

• A. Very short microvilli with a keratin core on stratified squamous cells
• B. Motile cilia with basal bodies in the bronchial epithelium
• C. Non-motile cilia involved in sensing
• D. Long microvilli with an actin core on columnar cells found in the epididymis and vas deferens

Answer: (D)

Stereocilia are long, non-motile protrusions on certain epithelial cells that resemble microvilli but are specialized for absorption and secretion. They have an actin filament core and do not beat, unlike cilia. In the male reproductive tract, specifically the epididymis and vas deferens, the surface of columnar cells is lined with these tall, fingerlike extensions to increase surface area for reabsorbing luminal fluid and concentrating sperm. This description matches long microvillous extensions with an actin core on columnar cells in those regions. Other options describe true cilia (motile or sensory) or microvilli with incorrect core composition, which don’t fit stereocilia.