Practice question

Sperm guidance in mammalian female tract involves chemotaxis and thermotaxis toward cumulus-oocyte complex. Cumulus cells surrounding ovulated egg secrete progesterone creating micromolar gradient increasing toward egg. Progesterone binds sperm ABHD2 hydrolase receptor removing 2-arachidonoylglycerol inhibition of CatSper channel, causing calcium influx, asymmetric flagellar beating and directional turn toward source. Estrogen and testosterone not chemotactic, oxytocin influences uterine contraction but not sperm steering. Thus progesterone serves dominant physiological chemoattractant coordinating hyperactivation and chemotaxis, ensuring preferential recruitment of capacitated sperm to fertilization site at ampulla and enhancing encounters with egg, mechanism conserved across mammals including humans.