Guys think about their penis a lot. We also spend quite a bit of time thinking about the penis of other guys. I don’t have any science to back this up, but it’s fairly self-evident that guys think a lot about dick.

But, how well do you know your penis?

Here’s some penis-related facts you might find useful in a pub quiz or if you’re running out of dinner party conversation.

What are the bits that make up the penis?

There’s three key parts that you need to be familiar with – Radix, Corpus, and Epithelium.

The root of the penis

This is referred to as the radix. The radix is the attached part, consisting of the bulb of penis in the middle and the crus of the penis, one on either side of the bulb. It lies within the superficial perineal pouch.

The body of the penis

This is referred to as the corpus. The corpus has two surfaces: dorsal - posterosuperior in the erect penis, and ventral or urethral - facing downwards and backwards in the flaccid penis. The ventral surface is marked by a groove in a lateral direction.

The epithelium of the penis

This consists of the shaft skin, the foreskin, and the preputial mucosa on the inside of the foreskin and covering the glans penis. The epithelium is not attached to the underlying shaft so it’s free to glide to and fro.

What’s the structure of the penis?

A man’s penis is made up of three columns of tissue  -  two corpora cavernosa lie next to each other on the dorsal side and one corpus spongiosum lies between them on the ventral side.

The enlarged and bulbous-shaped end of the corpus spongiosum forms the glans penis, which supports the foreskin, or prepuce, a loose fold of skin that in adults can retract to expose the glans. The area on the underside of the penis, where the foreskin is attached, is called the frenum, or frenulum. The rounded base of the glans is called the corona. The perineal raphe is the noticeable line along the underside of the penis.

The urethra, which is the last part of the urinary tract, traverses the corpus spongiosum, and its opening, known as the meatus, lies on the tip of the glans penis. It’s a passage both for urine and for the ejaculation of semen.

The raphe is the visible ridge between the lateral halves of the penis, found on the ventral or underside of the penis, running from the meatus  –  the opening of the urethra  -  across the scrotum to the perineum, which is the area between the scrotum and the anus.

The human penis differs from those of most other mammals, as it has no baculum, or erectile bone, and instead relies entirely on engorgement with blood to reach its erect state. It can’t be withdrawn into the groin, and it’s larger than average in the animal kingdom – in proportion to body mass.

How big should a penis be?

Measurements vary, with studies that rely on self-measurement reporting a significantly higher average than those with a health professional measuring. A 2015 review of 15,521 men  –  measured by health professionals  –  concluded that the average length of an erect human penis is 13.12 cm (5.17 inches) long, while the average circumference of an erect human penis is 11.66 cm (4.59 inches).

On entering puberty, the penis, scrotum and testicles will enlarge toward maturity. During the process, pubic hair grows above and around the penis. A large-scale study concluded that penile growth is typically complete not later than age 17, and possibly earlier.

Penis size difference is most likely caused by genetics, but there are some studies that suggest that environmental factors such as fertility medications, diet, or exposure to chemical pollution could have an impact.

Can I make my penis bigger?

The short answer is no – you’re pretty much stuck with what you’ve got.

Researchers from King’s College hospital in London, publishing their findings in the journal Sexual Medicine Reviews, have concluded that procedures to make penises larger do not work, are ineffective and risky, and leave many men physically or psychologically scarred. According to the researchers, there is scant evidence that the range of procedures men undergo in a bid to enlarge their penis actually produce that result. The treatments carry a high risk of complications, including permanent numbness, and most men who undergo penile extension are dissatisfied with the results afterwards.

Does it matter how big my penis is?

The more sexual encounters you have, and the more penises that you get to experience, the more you realise that there’s really not much correlation between size and pleasure. No matter what size you are, and no matter what size the other guy is, what matters is the sexual connection between you and not how big you are.

If you want to give your sexual partners and yourself some different experiences, try a sheath extension. There’s a number of different products out there, but essentially the sheath goes over the erect penis and adds length and girth.

How do erections work?

An erection is the stiffening and rising of the penis, which occurs during sexual arousal, though it can also happen in non-sexual situations. Spontaneous erections frequently occur during adolescence due to friction with clothing, a full bladder or large intestine, hormone fluctuations, nervousness, and undressing in a non-sexual situation. It’s also normal for erections to occur during sleep and upon waking.

The primary physiological mechanism that brings about erection is the autonomic dilation of arteries supplying blood to the penis, which allows more blood to fill the three spongy erectile tissue chambers in the penis, causing it to lengthen and stiffen. The now-engorged erectile tissue presses against and constricts the veins that carry blood away from the penis. More blood enters than leaves the penis until an equilibrium is reached where an equal volume of blood flows into the dilated arteries and out of the constricted veins; a constant erectile size is achieved at this equilibrium. The scrotum will usually tighten during erection.

How does an ejaculation work?

Ejaculation is the ejecting of semen from the penis, and is usually accompanied by orgasm. A series of muscular contractions delivers semen, containing male gametes known as sperm cells or spermatozoa, from the penis. It’s usually the result of sexual stimulation, which may include prostate stimulation. Ejaculation may occur spontaneously during sleep  -  this is known as a nocturnal emission or wet dream.

Ejaculation has two phases  –  emission, and ejaculation proper. The emission phase of the ejaculatory reflex is under control of the sympathetic nervous system, while the ejaculatory phase is under control of a spinal reflex at the level of the spinal nerves. A refractory period succeeds the ejaculation, and sexual stimulation precedes it.

What can go wrong with my penis?

As many as one in 10 men suffer from Peyronie’s disease.

Peyronie’s is an often painful scarring or bending of the penis that can make sex uncomfortable or impossible. It involves the growth of fibrous plaque, or harder tissue, in the walls of the penis. A ring of plaque can create an hourglass shape in an erection. A growth on one side can bring on a bend. In severe cases, the bend can be 90 degrees or more.

The condition, which is named after the 18th-century French surgeon who first studied it, tends to affect men in their 40s or older. It is thought to be a response to injury, perhaps during sport or vigorous sex. The trauma, which can go unnoticed at the time, causes the scar tissue to build up. Peyronie’s may also be genetic in some men, while studies have in some cases linked it to low testosterone.

Peyronie’s can cause significant shortening of the penis. Doctors say diagnoses have risen significantly in recent years as men become more comfortable seeking help. Treatment can be complex and uncomfortable – and can require invasive surgery.

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