Practice question

Rheotaxis is tendency of mammalian sperm to orient and swim against fluid current rather than randomly drifting. In oviduct, ciliated epithelium generates flow toward uterus, while sperm must migrate upstream toward ampulla where fertilization occurs. Shear stress sensing by flagellum triggers calcium signals via CatSper that reorients beating direction. This mechanism prevents washout, concentrates capacitated sperm near egg, and cooperates with thermotaxis and chemotaxis. Rheotaxis provides long-distance physical guidance ensuring sperm progress against outward fluid transport efficiently promoting encounter with ovulated oocyte complex during fertility window.