Erection: How Does It Work And When Does It Happen

Erection is a complex mechanism that, for centuries, has become part of mystic rituals and superstitions, as well as the measure of one's virility. But how does it work and why doesn't it always happen?

Most primates have a baculum, or ‘os penis’, which facilitates the sexual act – but not humans. It's believed that hominids lost it through sexual selection: the implication of not having a baculum means that only healthy males can mate, while unhealthy ones won't be able to have an erection.

In addition, humans have a much bigger penis as compared to the average size of other primates (e.g. the penis of a gorilla only reaches about 4 cm when erect), which makes maintaining an erection even more difficult.

How does male erection happen, then?

The penis is formed by three cavernous bodies. The two larger ones are wrapped in a layer of white tissue, flexible yet resistant, while below them we can find the smallest one, wrapped in a stretchier tissue, which contains the urethra. These cavernous bodies are like tanks and fill up with blood, swelling like balloons and getting harder.

They need to retain the blood in order not to lose the erection; as such, the tissue that wraps the largest cavernous bodies traps the veins, thus preventing the blood from flowing out.

That's not all: in order to increase the erection, there are also some special muscles – the ischiocavernosus and the bulbospongiosus – that enfold the base of the penis and squeeze it like a toothpaste tube, pushing the blood towards the tip.

How much does the size of the penis change during this process?

The difference from one person to another is enormous: some people's penis doubles in size, while for others it grows five times as big. This is why, when talking about these differences, we use the terms grower and shower – in some cases a small non-erect penis can grow a lot, while in others a big penis won't change much when turgid.

And if male erection doesn't happen?

Erectile dysfunction can be caused by vascular or psychological conditions (anxiety releases adrenaline, which shuts down the blood vessels in the penis), and sometimes it can also be due to muscular causes, as weak muscles in the pelvic floor can reduce or prevent the erection.

In these cases, the muscles and the pelvic floor can be retrained – not with the Kegel exercises (the rhythmic contraction and relaxation of pelvic muscles) we can learn through an app or watching a video, however. Rather, a specialised healthcare professional must be consulted, as trying to solve this all by yourself could actually make the problem worse.

Not all men know how their genital system works, yet, when it comes to sexual matters, they pretend that everything's fine. A healthy dose of curiosity and investigation – in physical terms, too – are the best way to get reacquainted with such a delicate system.


Article by Claudio Morandini – Physiotherapist, perineal rehabilitator, sex counsellor and sexual education specialist.

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