Sperm Structure and Semen Composition

Males release 2-5 ml of semen, a mixture of mature sperm and accessory gland fluids.

The 60 μm long mature sperm cells consist of the head, neck, midpiece, and tail.

The head of the sperm, measuring about 4 to 5 μm, is flattened and tapering.

It contains a nucleus with condensed chromosomes and the acrosome, a cap-like structure filled with enzymes for sperm to penetrate the egg.

A short neck between the head and midpiece contains centrioles, which form microtubules that extend into the midpiece and tail.

The midpiece has spirally arranged mitochondria, which provide the energy required for movement and metabolism.

The tail or flagellum propels the sperm in a whiplash movement to swim toward the egg.

Besides the sperm, the bulk of semen's volume is made up of a mixture of secretions from the seminal vesicles, prostate gland, and bulbourethral glands.

This slightly alkaline whitish fluid with a thick, sticky consistency nourishes the sperm and neutralizes the acidity of the vagina for sperm survival.

It also contains enzymes that prevent semen coagulation after ejaculation.