Sperm

Sperm, or spermatozoon, is the male gamete in sexually reproducing animals, including humans. Sperm cells are produced in the testes through a process called spermatogenesis and are delivered from the male reproductive tract in semen during ejaculation.

Anatomy: The sperm cell has a condensed nucleus in the head, which contains haploid DNA and is capped by the acrosome, a vesicle with enzymes that help penetrate the egg. The midpiece houses mitochondria for energy, and the tail, or flagellum, powers motility.

Function and fertilization: Sperm swim through the female reproductive tract to reach the oocyte. Fertilization occurs when a sperm binds to and penetrates the oocyte's zona pellucida and plasma membranes, catalyzed by acrosomal enzymes. Fusion of pronuclei combines genetic material to form a zygote; the oocyte completes meiosis soon after.

Production and viability: Spermatogenesis in the testes takes about 64–74 days and produces millions of sperm daily. In a favorable female tract environment, sperm may live a few days, typically up to five. External conditions and health affect sperm count and motility.