The Structure and Function of the Penis and the Mysteries of Scrotal Temperature Regulation
The fascia of the penis, from superficial to deep, consists of the superficial perineal fascia, the penile fascia, and the tunica albuginea. Among them, the tunica albuginea is the thickest and toughest, and it is closely related to penile erection.
The penis is innervated by both autonomic nerves (sympathetic and parasympathetic nerves) and somatic nerves (sensory and motor nerves). The main somatic nerves of the penis are branches of the dorsal penile nerve and the perineal nerve.
Somatic nerves primarily control sensation in the penile skin, foreskin, and glans penis, as well as the contraction of the bulbospongiosus and ischiocavernosus muscles. When the ischiocavernosus muscle contracts, it compresses the thickened corpora cavernosa, increasing intracavernosal pressure to achieve a firm erection; contraction of the bulbospongiosus muscle allows semen to be expelled from the body through the urethra.
The penis is highly adaptable. In its normal state, it is flaccid and short, and its shape can change with body posture. However, when sexually stimulated, the penis displays its erection. Due to changes in blood supply, it becomes erect, rapidly swelling from its flaccid state and throbbing. The whole process is like a limp tire being inflated and becoming very hard. When erect, the penis is straight, almost at a 90-degree angle to the abdomen, seemingly proclaiming masculine power.
The penis plays a crucial role in sexual intercourse and reproduction, making it of paramount importance to men. Internationally, the male gender symbol is "♂," where the "♂" represents the male penis. The relationship between the male penis and sperm is like that of a Long March rocket and a satellite; even the best satellite needs a rocket to launch it to its designated location to function. Similarly, male sperm must be ejaculated through the penis into the woman's vagina to fertilize an egg.
Men are generally very concerned about the size of their penis. Some men feel inferior because their penis is small and envy men with larger penises. So what size is considered normal? Research data shows that the longest penis in a flaccid state is 14.5 cm, the shortest is 4 cm, and the average is 8.4 cm. When erect, the largest is 16 cm, the smallest is 9 cm, and the average is 12 cm. Currently, there are no universally accepted numerical values for penis size. Interestingly, a flaccidly large penis does not show a significant increase in volume when erect, while a flaccidly small penis shows a more significant change in volume when erect.
When evaluating penile function, one should not focus on its length or girth, but rather on its ability to perform its intended function. It should be "ready to be summoned, ready to fight, and victorious in battle." When sexually aroused, the penis should quickly achieve an erection, firm enough for penetration, maintain the erection for a period of time, and ultimately ejaculate successfully. Generally, penile size is acceptable as long as it does not interfere with normal urination and sexual intercourse. However, it is important to note that the glans penis of an adult male must be exposed.
While some male organs, such as the nipples, have little physiological value, the penis serves the functions of urination and sexual intercourse. Men use their penis multiple times a day, and any problems with it not only cause distress for the man but also distress for his partner who cannot achieve a satisfying sex life.
Therefore, it can be said that a man's penis size and sexual function are related to his dignity.
**Scrotum that is sensitive and shy due to air conditioning**
Walking out of the green field
Emerging from a series of nightmares
Those eyes that shine brightly every day, hoping and watching intently.
A look of dejection tinged with the same sadness.
This round, inflated sac
I've loved, been hurt, suffered, and hated.
It's disappointing once again.
Hope after hope, forgiveness after forgiveness
This modern poem is titled "An Inflated Skin." Each of us has a skin like this, which grieves with the body's sorrow and rejoices with its joy. It experiences emotions like love and hate, and it expands and contracts. Just like the round, inflated skin in the poem, it too has loved, been hurt, suffered, and hated.
In fact, a man's scrotum is also a skin bag. It is shy and always hides behind the penis. It is pigmented, thin and soft, and has a septum in the middle that divides the scrotum into two chambers, each containing the testicles, epididymis and vas deferens.
The scrotum has many folds, resembling an old man covered in wrinkles. However, it is very agile, capable of contracting and expanding. Even more remarkably, it can regulate the temperature around the testicles (the temperature inside the scrotum is 1.5°C to 2°C lower than body temperature), which is beneficial for sperm production. Located below the base of the penis, this multi-layered sac houses and protects the testicles and epididymis, and is the male external genitalia.
From a comparative anatomical perspective, the gonads of male fish and birds are located within the body cavity, lacking a scrotum. Only in higher mammals do males have testes outside the body cavity, forming a scrotum. This is an evolutionary adaptation to the lower body temperature of the testes, which is more conducive to sperm production. The scrotal wall can be considered a continuation of the abdominal wall, its surface being skin, but lacking subcutaneous fat. Beneath the skin lies the dartos muscle tissue containing smooth muscle fibers.
The seminal vesicle and testicular tunica vaginalis, along with the dartos fascia and part of the fascia, extend deep into the scrotum at the midline, forming the scrotal septum, which houses the left and right testes respectively. The scrotal skin is thin and folded, dark brown in color, and the pubic hair is sparse and curly. The scrotal skin contains extremely abundant sebaceous glands and apocrine glands; these secretions, when interacting with bacteria of the vulva, can produce a distinctive odor.
The scrotal wall, with its rich folds, has considerable elasticity. In cold environments, the scrotum contracts, while in warm environments, it relaxes and expands, increasing sweat gland secretion, thus regulating the temperature inside the scrotum, which is beneficial for sperm production in the testes.
The scrotum is one of the male erogenous zones; during sexual arousal, it contracts, thickens, and elevates. Because the scrotum is located outside the skin, contains the important testes, and is richly innervated, it is very sensitive to external stimuli. Therefore, it is important to protect the scrotum from external forces (such as kicking, pushing, pinching, or punching). The scrotum is a continuation of the abdominal wall, divided into two sacs by a central septum. Each sac contains the corresponding scrotal segment of the testes, epididymis, and spermatic cord. The midline of the abdomen, also known as the scrotal suture, is the "fusion line" of the embryonic genital eminence.
The scrotal skin is rich in temperature receptors, acting as an "air conditioner" to regulate testicular temperature. The scrotum is characterized by its ability to easily contract and expand, thus regulating the local temperature of the testicles to remain 2-3°C lower than body temperature (the optimal temperature for sperm production). The scrotum has a rich blood supply, and blood flow increases significantly with temperature. When exposed to cold, the smooth muscles contract, the scrotal skin wrinkles, and the scrotum shrinks in size to reduce heat loss. Simultaneously, the scrotum moves closer to the abdomen, utilizing abdominal warmth for insulation.
When the body enters a high-temperature environment or is subjected to heat stimulation, the scrotum relaxes, the skin folds disappear, and the scrotum droops further. This is done to dissipate heat through sweating and to reduce contact with the abdomen, thus lowering the temperature. This self-regulation of the scrotum is not under conscious control; it is a spontaneous reflex process. Its main purpose is to ensure that the testicles are in a relatively suitable temperature environment, guaranteeing the production of both quantity and quality of sperm. Because the scrotum contains numerous skin folds and is located in a relatively poorly ventilated part of the body, it easily accumulates dirt and promotes bacterial growth; therefore, regular cleaning is essential.
The scrotum has a rich blood supply, with arteries primarily originating from branches of the femoral artery (external pudendal artery), branches of the perineal artery (posterior scrotal artery), and branches of the inferior epigastric artery (external spermatic artery). The arteries and veins of the scrotum run parallel to each other, draining into the internal pudendal vein and the dorsal penile vein. The blood vessels in the scrotum mostly run longitudinally and obliquely, and scrotal lymph drains to the inguinal lymph nodes. The scrotal nerves are branches of the lumbar plexus and perineal nerves. The testicular artery is a tortuous, conical spiral structure, its base adhering to the epididymis. A venous network emerges from the posterior border of the testis, forming a pampiniform plexus that enters the spermatic cord, surrounding the tortuous testicular artery and acting as a temperature regulator. This anatomical relationship provides an effective countercurrent mechanism, allowing arterial blood entering the testis to be cooled by venous blood leaving. The proximity of the arteries and veins to the surface of the testis further facilitates direct heat dissipation from the testis.