“God gave us a penis and a brain, but only enough blood to run one at a time.”
This funny quote made by Robin Williams was said jokingly of course, but expressions such “Boner” or “love muscle” just prove that both men and women have common misconceptions about penile anatomy. However, understanding how the penis functions can help get the most out of sexual relationships, whether learning about it for the first time or extending further existing knowledge.
The penis has two main functions:
- Sexual intercourse – during the phase of sexual arousal, the penis fills with blood which makes it rigid and erect, so as to enable vaginal penetration. During orgasm, sperm cells are ejaculated from the penis via the urethra, and subsequently the penis gradually regains its flaccid form.
- A urinary role – the penis contains the urethra, which allows passage of urine from the bladder to the urethral opening, from which it is expelled from the body.
What Are the Main Parts of the Penis
In this article, we will elaborate on the anatomy of the penis and the functions of its various parts. We’ll start with the fact that for both sexes, genital development begins at the fetal phase, as an undefined lump, from which either the male penis or the female clitoris develops – depending on fetal exposure to either male or female hormones. Changes in the appearance of the male fetus, as compared to the female one, begin to appear approximately eight weeks following conception.
The male reproductive system contains both internal and external components. The penis is an external organ which is made up of three parts: the root, the body (shaft), and the glans penis, and despite the common misconception, it does not contain any bones:
The Glans (Head of the Penis)
This is the cone-shaped end of the penis (often referred to as the “head”). Its name originates from the Latin word ‘acorn’, because it resembles the fruit of the oak tree. The glans penis is composed of an external skin tissue and its interior is made up of connective tissue and a high concentration of nerve endings and receptors, which make it the most sensitive part of the organ.
The glans penis is designed to assist penetration during sexual intercourse and to transmit a sense of stimulation to the ejaculation and orgasm center in the brain, so that semen can be expelled and sexual satisfaction be achieved. Although the sensitivity of the glans is obviously important, several studies have indicated that, in some men, increased sensitivity of the glans and shaft may contribute to premature ejaculation. Another interesting fact is that while the penis gets rigid during erection, the glans stays softer as it acts as a shock absorber during intercourse.
The glans penis consists of the following:
- Corona – those raised, rounded margins protruding from the base of the glans penis.
- Foreskin/Prepuce – a loose layer of skin that covers the glans penis. Nowadays, it is customary in many countries to surgically remove the foreskin in a procedure called circumcision, based on medical or religious grounds. As a result, the exposed external part of the glans turns dry.
- Frenulum – an elastic sheath of skin on the underside of the glans, connecting the foreskin and the corona. It is considered a highly erogenous zone (an area which generates a sense of pleasure) that is very sensitive to the touch.
- Neck of the glans – separating it from the shaft of the penis.
- Meatus – the opening of the urethra which is located at the very tip of the glans penis, through which urine is expelled when the penis is flaccid, and semen – during ejaculation.
The Shaft of the Penis
The shaft is the main external portion of the penis, extending from the root to the glans. Beneath the skin, it contains three columns of erectile tissue: two corpora cavernosa, positioned side by side, and the corpus spongiosum, which runs along the underside of the penis and surrounds the urethra.
The shaft also contains blood vessels, nerves and connective tissue that support its structure and function. Together, these anatomical components allow the penis to change in size and firmness during an erection.
The Root of the Penis
The root is the most proximal, fixed part of the penis and is located internally rather than being externally visible. It consists of the bulb and two crura, from which the erectile tissues of the penis extend.
The root is associated with muscles that contribute to erectile and urinary function. These muscles help empty residual urine or semen from the urethra and can also assist in maintaining an erection by supporting blood flow and pressure within the erectile tissues. Ligaments anchor the root of the penis to the pubic region and help provide structural support.
What Is Erectile Tissue?
Erectile tissue is specialised tissue within the penis that can expand as it fills with blood during sexual arousal. It contains a network of blood vessels and smooth muscle and forms the internal structures responsible for increasing the size and firmness of the penis during an erection.
The penis contains three main columns of erectile tissue: two corpora cavernosa and one corpus spongiosum.
Corpora Cavernosa
The corpora cavernosa are two cylindrical columns of erectile tissue that run alongside each other along most of the length of the penis. They contain a network of vascular spaces surrounded by smooth muscle and are enclosed by the tunica albuginea.
During sexual arousal, the smooth muscle relaxes and blood flow into the corpora cavernosa increases, causing them to expand. As pressure builds within these erectile bodies, the penis becomes larger and firmer. The corpora cavernosa therefore play a central role in producing and maintaining an erection.
Corpus Spongiosum
The corpus spongiosum is a single column of erectile tissue located along the underside of the penis. It surrounds the urethra — the tube through which urine and semen leave the body — and expands at its end to form the glans (head of the penis).
Like the corpora cavernosa, the corpus spongiosum fills with blood during an erection. However, it remains more flexible, helping to prevent the urethra from being compressed so that semen can pass through it during ejaculation.
What Is the Tunica Albuginea?
The tunica albuginea is a strong, elastic layer of fibrous connective tissue that surrounds the corpora cavernosa — the two erectile bodies that run along the shaft of the penis. It helps maintain the penis’s structure while allowing it to expand during an erection.
The tunica albuginea also plays an important role in maintaining penile rigidity. During sexual arousal, the smooth muscle within the erectile tissue relaxes, allowing increased blood flow into the corpora cavernosa. As these chambers fill with blood and expand, the tunica albuginea stretches and helps compress the veins responsible for draining blood from the penis. This reduces venous outflow, allowing pressure to build within the erectile tissue and helping the penis remain firm and erect.
This process forms an important part of the veno-occlusive mechanism that enables a healthy erection.
How Does Blood Flow Through the Penis?
Blood flow plays a central role in the erection process. The penis receives its arterial blood supply primarily through branches of the internal pudendal artery, including the cavernosal arteries that supply the erectile tissue within the corpora cavernosa.
During sexual arousal, the smooth muscle within the penile arteries and erectile tissue relaxes, allowing more blood to flow into the corpora cavernosa. As these erectile bodies fill and expand, pressure increases inside them. At the same time, this expansion compresses the veins that normally drain blood from the penis against the tunica albuginea, reducing the amount of blood that can flow out.
The combination of increased arterial inflow and reduced venous outflow allows pressure to build within the erectile tissue, helping the penis become and remain firm during an erection.
What Nerves Control the Penis and Erections?
The penis is supplied by a network of nerves that control sensation and play an important role in the erection process. These include autonomic nerves, which regulate involuntary functions such as blood flow, and somatic nerves, which carry sensory information between the penis and the nervous system.
During sexual arousal, parasympathetic nerve signals help relax the smooth muscle within the penile arteries and erectile tissue, allowing increased blood flow into the corpora cavernosa and contributing to the development of an erection. Sympathetic nerves are involved in processes including ejaculation and the return of the penis to its non-erect state.
Sensory signals from the penis are carried primarily through the dorsal nerve of the penis, a branch of the pudendal nerve. Together, these sensory and autonomic pathways coordinate the neurological and vascular responses required for normal erectile function.
How Does an Erection Work?
An erection is a coordinated process involving the nervous system, blood vessels, erectile tissue and the tunica albuginea. During sexual arousal, nerve signals cause the smooth muscle within the penile arteries and erectile tissue to relax, increasing blood flow into the corpora cavernosa.
As the corpora cavernosa fill with blood, they expand and press against the surrounding tunica albuginea. This compresses the veins that normally drain blood from the penis, reducing venous outflow while blood continues to enter. The resulting increase in pressure causes the penis to become larger and firm.
This process is known as the veno-occlusive mechanism. A healthy erection therefore depends on sufficient arterial blood flow, appropriate nerve signalling, functional erectile tissue and the ability to effectively restrict blood from leaving the penis.
How Is Penis Anatomy Related to Erectile Dysfunction?
A healthy erection depends on several anatomical and physiological systems working together. Nerves must transmit the appropriate signals, arteries must deliver sufficient blood to the penis, the erectile tissue must be able to expand, and the veno-occlusive mechanism must effectively restrict blood from flowing out of the corpora cavernosa.
Erectile dysfunction (ED) can occur when one or more parts of this process are impaired. Reduced arterial blood flow may make it difficult for the erectile tissue to fill sufficiently, while problems affecting the nerves can interfere with the signals required to initiate an erection. Changes in the erectile tissue or the mechanisms responsible for limiting venous outflow may also affect the ability to achieve or maintain sufficient penile rigidity.
Because erectile function involves several interconnected systems, ED can have different underlying causes and contributing factors. Understanding how these structures normally work together can therefore help explain why erectile difficulties occur and why identifying the underlying cause is an important part of assessing ED.
Frequently Asked Questions About Penis Anatomy
What are the main parts of the penis?
The penis consists of three main external parts: the root, shaft and glans (head). Internally, it contains erectile tissue, including two corpora cavernosa and the corpus spongiosum, as well as blood vessels, nerves, connective tissue and the urethra.
What tissue causes the penis to become erect?
The main erectile structures are the two corpora cavernosa, which run along the length of the penis. During sexual arousal, increased blood flow causes these tissues to expand. As pressure builds and blood outflow is restricted, the penis becomes firm and erect.
What is the function of the corpora cavernosa?
The corpora cavernosa are two cylindrical columns of erectile tissue responsible for most of the rigidity of an erection. They contain vascular spaces that fill with blood during sexual arousal, causing the penis to increase in size and firmness.
What is the tunica albuginea?
The tunica albuginea is a strong, elastic layer of fibrous connective tissue surrounding the corpora cavernosa. During an erection, it helps compress the veins that drain blood from the penis, reducing venous outflow and helping maintain penile rigidity.
How does blood flow create an erection?
During sexual arousal, nerve signals cause smooth muscle in the penile arteries and erectile tissue to relax, allowing more blood to enter the corpora cavernosa. As they expand, veins that normally drain blood from the penis are compressed, reducing blood outflow and increasing pressure within the erectile tissue.
What nerves are involved in an erection?
Erections involve both autonomic and somatic nerves. Parasympathetic nerve signals help increase penile blood flow, while sensory nerves carry information between the penis and the nervous system. Sympathetic nerves are involved in ejaculation and the return of the penis to its non-erect state.
What part of the penis contains the urethra?
The urethra runs through the corpus spongiosum, a column of erectile tissue located along the underside of the penis. The corpus spongiosum expands at its end to form the glans and helps prevent the urethra from becoming fully compressed during an erection.
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