Spermatozoi

Spermatozoi (spermatozoa) are the male gametes of animals. They are haploid cells produced by spermatogenesis in the testes and deliver the paternal genome to the female ovum during fertilization.

A typical sperm has a small head containing the haploid nucleus and an acrosome, a midpiece packed with mitochondria, and a tail or flagellum that provides motility. In humans, the total length is about 50–60 micrometers.

Spermatogenesis occurs in the seminiferous tubules of the testes. It includes meiosis and spermiogenesis, wherein spermatids become mature spermatozoa. Spermatogenesis is regulated by hormonal signals from the hypothalamus-pituitary axis, notably FSH and testosterone.

Spermatozoa are stored and mature in the epididymis, acquiring motility. During ejaculation they enter the female reproductive tract, where capacitation and the acrosome reaction enable fertilization of an oocyte.

During fertilization, a spermatozoon binds to and penetrates the zona pellucida and oolemma, delivering its paternal genome. Fusion of genetic material forms a zygote, which begins embryonic development.

Semen analysis evaluates sperm count, motility, and morphology and is used in fertility assessments. Abnormal results can indicate male factor infertility; methods include lifestyle changes, medical treatment, or assisted reproductive techniques.