Spermatozoïde

Spermatozoïde is the male gamete in animals; in English it is called the sperm cell. It is a compact, haploid cell produced through spermatogenesis in the testes and is designed to deliver the paternal genome to the oocyte during fertilization. In humans, each sperm carries 23 chromosomes.

Anatomically, a mature spermatozoïde consists of a head, midpiece, and a tail (flagellum). The head contains a condensed nucleus with paternal DNA and an acrosome, a cap that contains enzymes to help penetrate the oocyte's outer layers. The midpiece houses mitochondria that supply energy for movement. The tail is a flagellum powered by axonemal microtubules that enables propulsion.

Spermatogenesis begins with spermatogonia in the seminiferous tubules of the testes, progressing through meiosis to form haploid spermatids, which differentiate during spermiogenesis into mature spermatozoïde. After release into the lumen, spermatozoïde gain motility and are stored and further matured in the epididymis, where they acquire full fertilizing capability.

Before fertilization, spermatozoïde undergo capacitation in the female reproductive tract, a biochemical change that enables the acrosome reaction. During fertilization, the acrosome releases enzymes that help penetrate the zona pellucida, the oocyte's surrounding layer, followed by fusion of sperm and oocyte membranes and delivery of the paternal genome.

Sperm quality and quantity influence fertility and are commonly assessed in semen analyses. Sperm lifespan in the female tract is limited, typically up to about five days, though viability varies.