Zaadcel

Zaadcel (sperm cell) is the male gamete in sexually reproduing organisms, including humans. Its primary role is to deliver paternal genetic material to the female gamete during fertilization. Mature human sperm measure about 50–60 micrometers in length and consist of a compact head, a midpiece rich in mitochondria, and a long tail (flagellum) that enables motility. The head contains a haploid nucleus with 23 chromosomes and an acrosome, a cap-like structure filled with enzymes that help penetrate the egg's outer layers.

Development occurs in the testes through spermatogenesis, involving mitotic and meiotic divisions and a final differentiation called spermiogenesis. This process starts at puberty and takes about 64 days in humans. Spermatozoa then move to the epididymis, where they acquire motility and fertilizing capability during a maturation period of about a week or two. During ejaculation, millions of sperm are released together with seminal fluid; individual sperm may survive for up to several days in the female reproductive tract, depending on conditions.

Fertilization occurs after capacitation in the female tract, followed by the acrosome reaction, which enables the sperm to penetrate the zona pellucida and fuse with the oocyte membrane, delivering the paternal genome to form a zygote.

Clinical context: semen analysis assesses concentration, motility, and morphology. Reference values vary by guidelines, but thresholds commonly cited include a concentration near 15 million sperm per milliliter as a lower reference limit; total motile sperm and the proportion of normal forms are also measured to evaluate fertility.