Kevin McEleny
Kevin McEleny
Ph.D FRCS FRCS (Urol), Newcastle Hospitals

Male reproductive system – How does it all work?

Testicles and sperm

The testicles (or testes) are two oval structures that are located within the scrotum. The reason that the testicles are outside body is that the optimum temperature for making sperm is slightly lower than body temperature. If the testicles were to remain inside the body, sperm production would be affected.

If the testicles do not descend correctly into the scrotum during early infancy, they are described as being undescended. If this happens your doctor may advise that an operation be carried out to place them in the scrotum. This procedure (called an orchidopexy), usually takes place in infancy, to try to prevent irreversible changes to the testicles’ development. Sometimes it isn’t possible to place them in the scrotum and they may need be removed, because of a risk of cancer later in life.

What do the testicles do?

The testicles, which are in the scrotum, do two things:

  • They make the male hormone testosterone
  • They make sperm

Testosterone is very important for men. Having the right amount of testosterone is critical to making sperm. It also helps build and keep muscle, stimulates bone development, helps maintain heart (cardiovascular) health, and red blood cell production. It also helps a man’s mood, concentration, sleep and sexual functioning.

Both testosterone and sperm production are controlled by hormones that come from the brain. There is a sequence to the events that lead to sperm production.

  1. In the brain, an area called the hypothalamus tells a structure called the pituitary gland to release hormones into the blood stream. These hormones include Luteinizing Hormone (LH), which tells the testicles to make testosterone and Follicle Stimulating Hormone (FSH), which tells the testicles to make sperm
  2. If the testicles are making testosterone and sperm normally, the brain receives a signal telling it this so it can then regulate the production of LH and FSH. This is a bit like a central heating system. If a room is too hot, the thermostat switches off the boiler so that the room temperature will drop back to normal. If the room gets too cold, then the thermostat switches the boiler on again

How do anabolic steroids harm fertility?

Anabolic steroids used for body building switch off the brain’s ability to make LH and FSH. This means that sperm production and natural testosterone production (needed for good sperm production) are blocked. Read more about it here.

How does the body make sperm?

Sperm production is a complex process. Basically, cells within the testicles undergo a number of changes during which, the chromosomes within the cells (the parts of the cell that contain DNA) form a single set, rather than a double set found in other body cells. The cells themselves pass through a number of specific changes, resulting in the very specialized appearance of sperm cells that enables them to travel through the female reproductive tract in their quest to encounter an oocyte (egg cell).

Axis of what happens in the testicles

Once sperm has been made, (the entire process takes about 2 and a half months) they are stored in a coiled tube that drains the testicle. This is called the epididymis and it is here that sperm gains the ability to move. When a man has sex/orgasms, the sperm in the epididymis passes through to the vas deferens, which connects the testicles to the base of the penis, where two structures called the ejaculatory ducts drain the fluid into the urethra, which is the tube through which urine  passes when a man goes to the toilet. The semen (containing sperm) is then ejaculated out of the end of the penis.

Male anatomy incl. the testicles

Where does semen come from?

The fluid that comes out after ejaculation contains a lot of things. In addition to the sperm (which is only 1-2% of the fluid’s volume, and comes from the testicles), nearly all the rest comes from the prostate gland and the seminal vesicles. These are structures found inside the male pelvis, located close to the bladder. These fluids are needed to help sperm in the fertilization process once in the female body.

Are low volume (smaller) testes linked to fertility problems?

Most of testicular tissue is made of the components that make sperm and these areas are more vulnerable to any type of problem. If a man’s testicular volume is low (less than about 15 mL), then if he has a sperm quality issue, it is likely that this is due to a sperm production-type problem, rather than a blockage. A thorough exam from a urologist can determine if a man has smaller testes.

What problems can you get in the scrotum?

The scrotum is the sac that contains the testicles. Sometimes there are problems that can be found when a semen analysis is poor, so it is very important to get an examination from a urologist.

Cancer: Sometimes men who have low sperm counts are may be at risk for testes cancer, though it is still rare. This means that it is important for men to examine their testicles on a regular basis and let their family doctor know, if they notice any new lumps. Cancers of the testicle occur in the testes. They feel like hard and irregular lumps.

Other reasons for scrotum swellings:

  1. Epididymal cysts: Fluid-containing cysts that arise in the epididymis Sometimes these cysts can be painful, but usually they cause no harm and should be left alone
  2. Hydrocele: Where an excessive amount of fluid accumulates around the testicle, leading to swelling. They usually cause no harm, but large ones can be unsightly or uncomfortable
  3. Varicocele: Enlargement of the scrotal veins; these are a bit like varicose veins and are caused by the valves that prevent back flow through veins not working. Sometimes they can cause discomfort or affect sperm quality
  4. Infection: causes pain and sometimes urinary symptoms

If you notice anything unusual in your testicles, you should see your doctor immediately. Serious problems can be quickly ruled out by a simple examination and scan. Genital infections can affect your own fertility as well as your partners and so need to be diagnosed and treated as soon as you get symptoms.

You can read more about erections and getting sperm to meet the egg in the woman in this article.