What Is A Penis?
The penis is part of what’s often called ‘male sexual anatomy’, although people of all genders can have penises! While technically the scrotum (often called the ballsack in casual conversation) is a separate piece of anatomy to the penis — the term referring only to the shaft — the two are closely intertwined in how many people think and talk about their bodies, so we’ll discuss the anatomy of both.
A penis typically is used for two primary functions— passing urine and sexual pleasure.
Did you know that ‘glans’ — the term used for the head of a penis — means ‘acorn’ in Latin? As its name suggests, the glans is often described as acorn-shaped, mushroom-shaped, or as a cone, but can vary in shape and size. This spongy tissue is the most sensitive erogenous zone on the body for most people with penises (although we’ll talk about the exceptions in a moment), and contains the urethral opening, through which urine, semen, and pre-ejaculate exit the body. Some people enjoy their urethral opening being penetrated, in a sex act known as ‘sounding’.
Another sensitive area for many people with penises is the frenulum. This is a band of tissue on the underside of the glans, and (for people who have one) connects the glans to the foreskin. The foreskin is loose skin around the head of the penis that protects it— sometimes this is removed for medical, cultural, or religious reasons, in a practice known as circumcision.
The part of the penis that runs from the glans to the base of the penis is called the ‘shaft’. When a penis is flaccid, the skin of the shaft can feel loose and look wrinkled, but it becomes smoother and more stretched out when a penis becomes erect.
Below the shaft sits the scrotum or scrotal sac, a two-chambered sac of muscle and skin that holds the testicles. The scrotum is external to the body as this helps keep the testicles at the right temperature to make and storm sperm! While some people may feel self-conscious about asymmetrical testicles (just as some people are self-conscious about asymmetrical labia), this is perfectly normal— it’s actually more common to have one testicle sit lower than the other. The scrotum is sensitive to temperature, and will tighten both in response to cold temperatures and when a penis is erect.
While we talked about the shaft of a penis being one structure in terms of external anatomy, it’s actually multiple structures internally. It consists of the urethra, three spongy like areas of erectile tissue (one of which surrounds the urethra), nerves and blood vessels that surround the erectile tissue, and layers of skin around all of them.
The erectile tissue that surrounds the urethra is known as the corpus spongiosum, while the other two areas of erectile tissue are known as corpus cavernosum. During an erection, these tissues fill with blood and swell, making the penis larger, harder, and more angled out from the body.
Within the ballsack, there are two egg shaped glands called the testicles or testes. As well as sperm, the testes produce hormones such as testosterone, oestrogen, and progesterone— while popular culture often portrays testosterone as a ‘male’ hormone and oestrogen and progesterone as ‘female’ hormones, everybody has some amount of all three in their bodies.
The two tubes that carry sperm out of the testicles are called the vas deferens, and the space they sit in within the body are called the inguinal canals. If you’ve heard of balls ‘dropping’, this actually refers to testicles descending from the inguinal canals. Some people enjoy their inguinal canals being penetrated and/or stimulated, in a sex act known as muffing.
While not part of the penis, I do want to talk about the prostate for a moment. When the vas deferens meet another structure called the seminal vesicles, they form the ejaculatory ducts, which pass through the prostate. The prostate is responsible for producing the fluid that transports and nourishes sperm, known as seminal fluid.
While we’ve talked about the average penis so far, it’s important to note that some penises are surgically constructed or modified. And surgically constructed or modified penises are just as much ‘real’ penises as those that aren’t!
The most obvious example of this is post-bottom surgery trans men and transmasculine people, who do not have the same internal anatomy as we’ve talked about. However, having a surgically constructed penis is not a trans-exclusive experience — phalloplasty (one of the bottom surgery options for trans men and transmasculine people) can also be performed on cisgender men who, for example, have lost or damaged their penises in accidents. In fact, the technique of phalloplasty was first created for cisgender men, before it was then adapted for trans men and transmasculine people!
Phalloplasty uses a skin graft to create a phallus. While the external anatomy is similar to that of non-surgically constructed penises, internally it has a very different structure. Because post-phalloplasty penises don’t contain any erectile tissue, an erectile device is often implanted. This is usually either a pump system (with the pump usually being placed within a testicle prosthetic) or a semi-rigid malleable implant, although some people choose not to have an erectile device implanted. Trans men and transmasculine people who have a phalloplasty can choose to have their clitoris ‘buried’ in the base of the new phallus— as a result, many post-phalloplasty trans men/transmascs find they are more sensitive near the base of their penis rather than at the head.
Another option for bottom surgery for trans men and masculine people is metoidioplasty, which uses the existing clitoris to make a micropenis. This can get erect without the use of an implant, as it uses the erectile tissue that also exists in the clitoris. However, the testicles of a post-metoidioplasty penis are silicone prosthetics, and as a result a post-metoidioplasty penis does not have vas deferens.
As well as these surgeries to create penises, some surgeries modify the anatomy of the penis. An orchiectomy (or sometimes orchidectomy) is a surgical procedure that removes one or both testicles, often to treat or prevent cancer (testicular, breast, or prostate) or as part of transition for trans women and transfeminine people, as it removes the need to take a testosterone blocker.
Another common example of surgical modification of the penis is a vasectomy. This procedure prevents somebody with a penis from being able to impregnate somebody else, by cutting, blocking, or sealing the vas deferens.
Variation Between Penises
Even for penises that haven’t been constructed or modified surgically, there’s a ton of variation. Just as vulvas and vaginas have a huge variety of shapes and sizes, so too do penises. It’s completely normal and natural! Your (or your partner/s’) penis varying from any cultural model of an ‘average’ or ‘ideal’ penis isn’t something to be ashamed of.
This variation can include the relative size of different parts of a penis, with some penises narrower at the head than at the base, some with the opposite relationship, and some with a relatively even size from tip to base. Some penises curve to one side more than the other, or angle up or down to different degrees when erect.
Because of the way our culture talks about penises, we often have a warped idea of what the average penis size is like— 85% of cis men seeking penile enlargement in one study had overestimated the average size. In fact, the average penis is between 5.1 and 5.5 inches long when erect, with researchers believing the average falls close to the lower end of that range.
Another area of variation when it comes to size is between ‘growers’ and ‘showers’. Somebody being a ‘grower’ means that the difference between their penis size when flaccid and erect is significant, while ‘showers’ have little or no difference in their flaccid and erect size. People who are post-phalloplasty are ‘showers’, as their penises don’t contain the kind of erectile tissue that swells as blood flows to the area during arousal.
Male Genital Anatomy – Boston University School of Medicine
Testes – You and Your Hormones
What to Know About Metoidioplasty – MedicalNewsToday
Orchiectomy – Cleveland Clinic
Vasectomy – Cleveland Clinic
Penile Prosthesis – Andrology
Gland Penis – Healthline
Scrotum Overview – Healthline
Corpus Spongiosum – National Cancer Institute
Corpus Cavernosum – National Cancer Institute
How does the prostate work? – National Library of Medicine