Key Functions and Detailed Structure of the Penis
The penis is the copulatory organ in male mammals and is also the organ responsible for urine discharge from their body. While in higher vertebrates this organ is called the penis, in lower invertebrates the corresponding structure is often referred to as cirrus.
Penis Structure
A part of the penis is outside the body and the other part is inside. The internal part of the penis is attached to the bony edges of the pubic arch which is the front part of the pelvis, at the base of the trunk. This internal part is called the root of the penis. The external part of the penis, called the body of the penis, is pendulous and is covered by skin.
Penis Anatomy
The penis anatomy is segregated into two parts: the external portion or the body and the root. The root of the penis has two projections (crura) and the bulb of the penis. The crura are joined to the edges of the pubic arch and the bulb is attached to the perineal membrane that makes the base of the trunk. The location of the penis root is right under the bulbourethral glands with the corpus spongiosum (or corpus cavernosum urethrae). It is a long cylindrical body of tissue that runs through the body of the penis right to its tip. At this point, it forms a mushroom-shaped structure that is termed a glans penis. The base of the glans penis has the corona (projecting margin).
The urethra is a tube that passes through the center of the corpus spongiosum. It provides the common route for the passage of both urine and semen. At the tip of the glans penis, the urethra provides a slit-like opening. At the sides of the bulbourethral glands, there is a pair of long cylindrical parts called the corpora cavernosa. They course through the body of the penis and located at the sides and in the area directly above the corpus spongiosum. The corpora cavernosa ends right before the glans penis. The groove where the corona is overhanging the corpora cavernosa is called the neck of the penis.
The penis anatomy has been illustrated in the penis diagram below.
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The corpora cavernosa has empty spaces that are divided by tissue partitions. These are made of collagen (fibrous protein), muscle, and elastic fiber. The corpora cavernosa are called erectile tissue since, at the time of sexual excitation, blood flows and fills their empty spaces, expanding their fibrous tissue. This blood is normally allowed to flow out by the blood vessels but their constriction holds the bloods in the penis for some time. This process enlarges and hardens the penis, making it erect due to the increased blood pressure.
The corpora cavernosa and corpus spongiosum are both covered by a circular layer of elastic tissue that is covered by a thin layer of skin. This skin is slightly darker than the rest of the body, is loose, and gets folded when the penis is in a flaccid state. The glans penis has a circular fold of skin where it begins. This skin is commonly known as the foreskin (prepuce) and it extends further to cover the glans.
Blood Supply to the Penis
The penis gets its blood supply from the internal pudendal artery which is a branch of the internal iliac artery. This artery supplies blood to the pelvic structures and organs and the inside of the thighs. The penis also has sensory and autonomic (involuntary) nerves. In the autonomic nerve fibers, the parasympathetic fibers cause the dilation of the blood vessels while the sympathetic fibers cause their constriction. The sympathetic system causes ejaculation which inhibits the desire to urinate at the time of erection and prevents the semen from entering the bladder at the same time.
Types of Penis
Some penises are straight at the time of erection while others have s slight curvature. Both types of penis are perfectly normal. There are three categories of a curved penis:
Curved downward from the base of penis.
Curved upwards from the base.
Curved to the left or right.
FAQs on Penis Anatomy: Structure, Blood Supply & Types
1. What are the main external and internal parts of the human penis?
The human penis is composed of three main external parts: the root, which attaches it to the abdominal wall; the body or shaft, which is the main part; and the glans penis, which is the sensitive, conical tip. Internally, the shaft contains three columns of erectile tissue: two corpora cavernosa on the dorsal side and one corpus spongiosum on the ventral side, which also surrounds the urethra.
2. What is the difference between the corpora cavernosa and the corpus spongiosum?
The corpora cavernosa and corpus spongiosum are both types of erectile tissue but have distinct functions and structures:
Corpora Cavernosa: These are two columns of spongy tissue located on the upper side of the penis. During an erection, they fill with a large volume of blood, causing the penis to become rigid and erect.
Corpus Spongiosum: This is a single column of tissue located on the underside of the penis that encloses the urethra. While it also engorges with blood, it remains less rigid to ensure the urethra stays open, allowing for the passage of semen during ejaculation.
3. How does the unique structure of the erectile tissues facilitate an erection?
The process of erection is a neurovascular event. Upon sexual stimulation, nerve signals cause the arteries supplying blood to the penis to dilate. This allows blood to rush into the sponge-like spaces of the corpora cavernosa at a high rate. As these tissues fill and expand, they press against the veins that normally drain blood away, effectively trapping the blood. This increased pressure and volume of blood cause the penis to become firm and erect. The corpus spongiosum's ability to remain pliable is crucial as it prevents the urethra from being compressed shut.
4. What are the two primary biological functions of the penis?
The penis serves two main biological functions:
Urination: It acts as a conduit for the urinary system, allowing urine to be expelled from the body through the urethra.
Reproduction: It functions as the male copulatory organ, designed to deliver semen into the female reproductive tract during sexual intercourse to facilitate fertilisation.
5. Does the penis contain muscles, and what is their role?
This is a common point of confusion. The shaft of the penis itself does not contain skeletal muscles; its erection is achieved through blood engorgement of the erectile tissues. However, there are important muscles located at the base of the penis, such as the bulbospongiosus and ischiocavernosus muscles. These muscles are crucial for functions like stabilising the erect penis, ejaculation (by contracting rhythmically to expel semen), and helping to empty the urethra of any remaining urine.
6. What is the significance of the glans penis and the prepuce?
The glans penis, or the head of the penis, is highly sensitive due to a high concentration of nerve endings, making it central to sexual arousal. It contains the external urethral opening. The prepuce, also known as the foreskin, is a retractable fold of skin that covers and protects the glans. It also has glands that produce smegma, a natural lubricant.
7. Why is maintaining proper hygiene, especially under the foreskin, important for preventing conditions like balanitis?
The space under the prepuce (foreskin) can trap moisture, dead skin cells, and a natural secretion called smegma. If not cleaned regularly, this accumulation can create an environment for bacteria and yeast to thrive, leading to inflammation and infection. This condition, known as balanitis (inflammation of the glans), can cause redness, swelling, and discomfort. Proper hygiene by retracting the foreskin and cleaning the area prevents this buildup and significantly reduces the risk of such infections.
8. How are the functions of the penis supported by its nerve and blood supply?
The penis relies on a specialised nerve and blood supply. The primary blood supply comes from the internal pudendal artery, which delivers the high volume of blood needed to fill the erectile tissues and cause an erection. The nerve supply, mainly from the pudendal nerve, is crucial for both sensation and function. It transmits sensory information (like touch and temperature) from the skin to the brain and carries motor signals from the brain and spinal cord to control erection and ejaculation.
