The testicles are two small oval-shaped organs suspended below the penis in a pouch of skin called the scrotum. They are part of the male reproductive system. From the start of puberty the cells lining the collecting tubules of the testicles produce sperm.

The collecting tubules inside the testicle join together to form a tube called the epididymis. This tube carries on to the outside of the testicle where it widens. It can be felt as a soft swelling at the back of the testicle. The wider part of the tube is called the spermatic cord. At its end, this forms a short tube called the ejaculatory duct. This duct joins the urethra (the tube from the bladder to the penis) just above the prostate gland.

The testicles also produce the hormone testosterone. This hormone maintains sex drive (libido) in men and is the main cause of the development of male characteristics such as:

• a deep voice
• beard growth
• muscle development
• the ability to have an erection.

Lymph fluid from the testicles drains to a group of lymph glands at the back of the abdomen.