spermatozoa

Spermatozoa are the male gametes of animals, specialized for fertilization. They are haploid cells produced by spermatogenesis in the testes and are adapted to deliver the paternal genome to the oocyte. A typical sperm has distinct regions: a compact head containing a highly condensed nucleus, and an acrosome with enzymes that help penetrate the egg’s outer layers; a midpiece rich in mitochondria to supply energy; and a tail, or flagellum, that provides motility through whip-like movements driven by the axoneme’s microtubule structure.

Development and maturation occur in stages. Spermatogenesis takes place in the seminiferous tubules of the testes, culminating in spermiogenesis, where round spermatids differentiate into elongated, mature spermatozoa. Mature spermatozoa are transported to the epididymis, where they gain motility and fertilizing capacity and are stored until ejaculation.

Function and fertilization involve specialized processes. During ejaculation, sperm travel through the male reproductive tract in seminal fluid. In the female reproductive tract, they may undergo capacitation, followed by the acrosome reaction, which enables the enzymes to penetrate the zona pellucida and allow fusion with the oocyte membrane, delivering the paternal haploid genome to form a zygote.

Clinical and reproductive relevance includes semen analysis to assess concentration, motility, and morphology; evaluation of male fertility; and assisted reproductive technologies such as intracytoplasmic sperm injection. Sperm production is continuous after puberty, with high daily yields; sperm survive for up to several days in the female tract but only minutes to hours outside the body.