Male reproductive system

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Before we delve into what might be going wrong, we thought it could be helpful to do a short recap of the male reproductive system (afterall, some of us might have been otherwise occupied during sex ed at school).


Sperm are the male reproductive cells - your equivalent of eggs.

Normal, mature sperm are highly specialised cells approximately 0.05mm long with three main parts: head, neck and tail. In fact, they are so small they win the prize of smallest cell in the human body.

Sperm technical illustration - Genea

In the head of the sperm is a structure called the nucleus, which contains 23 tightly packed chromosomes (the genetic material). The head of the sperm is designed to bind to and then enter (penetrate) the egg.

The neck joins the head to the tail. The part of the tail nearest the neck contains the mitochondria, which provides the energy for the sperm to move (motility). The tail moves in a whipping motion to propel the sperm towards the egg.

Reproductive tract

The male reproductive tract is made up of the testes, a system of ducts (tubes) and glands opening into the ducts.

The testes (singular: testis) are a pair of oval shaped glands that sit in the scrotum outside of the body next to the base of the penis. They have two related but separate roles:

  • production of sperm
  • production of the male sex hormone, testosterone.

Each normal testis is 15 to 35ml in volume and contains a number of tightly coiled, fine tubes called seminiferous tubules. The cells in the lining of the seminiferous tubules divide over and over again to produce sperm.

The epididymis is a long, highly-coiled tube which connects the seminiferous tubules to another single tube called the vas deferens. The sperm spend two to 10 days passing through the epididymis. During this journey, the sperm mature and gain the ability to move. It takes about 70 days in total for sperm to develop into the mature sperm found in semen that are capable of fertilising an egg.

The glands aid in the maturation, nourishment and transport of the sperm through the male reproductive system and into the female's body for fertilisation.

The ejaculate of fertile men contains tens of millions of sperm. However, men with much lower numbers of sperm can still achieve pregnancies. 

For more information about the male reproductive system, take a look at our infographics which describes sperm health, male reproduction and more.