Know your Body: Human Penis
Know your Body

Know your Body: Human Penis

Dr.Surya Rao Poodipeddi profile Authored by Dr.Surya Rao Poodipeddi on 10 Dec 2014 - 13:47.

The penis and scrotum are the external sexual organs of men.The human penis differs vastly from those of animal race with vast variations amongst those in their own race.

Function: The penis has a dual role to play. It acts as an outlet for the passage of urine whenever triggered by the full bladder through nervous mechanism. It acts as the outlet for the vital fluid called semen which contains the life giving sperm cells during sexual intercourse between man and woman.

It is interesting to note that one cannot pass urine while indulging in sexual intercourse in as much as he cannot pass semen during the act of urination simultaneously. The pathway for both is the same, the male urethra. However the mechanism and modus operindi are different. For urination the bladder has to be full and the sphincter has to act and open up for urine to be released. It combines voluntary as well as involuntary actions. Voluntary when the person knows he has to go to the toilet to ease himself.

Involuntary because we have no control to hold a full bladder and may ease in the pants if we don’t reach a toilet before it is too late! For releasing the semen a process called ejaculation, the same pathway comes into the picture. However, the process of ejaculation needs two important acts namely sexual intercourse (or masturbation) a nervous mechanism called orgasm and a message from the nervous pathways to ejaculate.It is this ejaculation of semen within the vagina of a female where the penis plays its role through what we call sexual intercourse. For intercourse to take place the penis becomes large and stiff a process called erection.Without an erect penis, penetration and intercourse are just impossible. Without intercourse semen can never be ejected inside the female vagina. Without ejection of semen chances for pregnancy are nil. This explains the importance of a functional penis.

Ejaculation of semen has two important roles. One is the sexual pleasure and the orgasm experienced by both the partners during sexual intercourse. The other and the very important role is supply of sperms one of which fertilizes an egg for the off spring to be born. In either case a fully functional penis is as important as life itself. It may not be possible to initiate pregnancy if there is defective mechanism of ejaculation or there is absence of sperms in the fluid. However without an erect penis one can never get or give sexual pleasures. If this happens the man is labeled as impotent.

Though the size of a functional penis varies indifferent persons of the same race and different races like the Africans who are known to have huge sizes research indicates that the average size of a penis ranges around 15 cm. In 90% of men the size varies between 13 and 18 cm. There is recorded evidence to show the existence of a functional penis whose size varied between 1.5 cm and 30 cm.


Having said so much about the importance of a penis in a male, one should know about different parts of a normal penis. The penis consists of mainly three parts, the head (Glans), the corona (junction) and the shaft. The shaft of the penis which is covered by retractile skin houses the corpus spongiosum, a paired corpora cavernosa, the penile part of the urethra, the blood vessels and nerves.

The various parts of a penis are:

Glans: The head of the penis is called glans penis. It is reddish and glistening. In a fully erect penis it looks like a crown adoring the body of the penis.The glans is highly sensitive. 

The prepuce otherwise called foreskin a thick fold of skin covers the glans. In an uncircumcised penis the prepuce fully covers the glans. 

Corona: A thick ridge called the corona connects the glans to the shaft of the penis. 

Frenulum: A thin strip of flesh on the underside of the penis that connects the shaft to the head is called the frenulum(or frenum). 

The urethra (or meatus) is the opening at the tip of the penis to allow the passage of both urine and semen. 

Smegma is a collection of a substance with the texture of cheese which is secreted by glands on each side of the frenulum in uncircumcised men.

Scrotum though literally not a part of the penis is an important external genital organ which houses the two testes that manufacture sperm and keeps the sperms protected by maintaining approximately 34C temperature.

Mechanism of erection:

It is very important to understand the mechanism involved in the erection of a penis.Erection of the penis occurs due to temporary increase in the blood flow and the resultant blood getting trapped within the penis leading the penis to elevate and enlarge. The process starts as a response to sexual stimulation. In a flaccid state of the penis the sponge like system of irregular vascular spaces that lie between arteries and veins get collapsed and contain very little blood. During erection these cavities become larger and get distended with blood. This is the immediate mechanism of erection.

Rigidity of an erect penis depends on maintaining high blood pressure in the cavernous bodies. This in turn depends on the veins. The blood flux system must close to avoid its escape without which the erection cannot be maintained. Any defect in this mechanism due to some disease of the arteries of the penis is responsible to cause erectile dysfunction and is termed as vasculogenic impotence. Erection of penis is the final objective for a successful sex act. It is achieved by an integrated synchronized action of several factors namely psychological, neuronal, hormonal, vascular and cavernous smooth muscle systems.

The corpus spongiosum and corpora cavernosa play important role in the erection of penis as well as flaccidity after the sex act or the sex stimulus is over. A series of mechanisms are involved both in the erection and flaccidity of the penis.

Conditions affecting penis:

A galaxy of conditions affects the penis. To mention afew important conditions we divide them into the following categories.

1.Those involving sexual act:

Erectile dysfunction. In this condition there isabsence of erection. The causes are many and need thorough evaluation with the help of a sexologist and andrologist. It is the most common condition affecting millions of population leading to frustration,ridicule and separation.

Premature ejaculation: Emission of semen very early or in extreme cases even before penetration. This needs an andrological study.

Disorders involving sperm counts: Again requiresanthologist’s services.

Priapism: Just opposite of erectile dysfunction where there is sustained erection of the penis causing embarrassment. This could be due to hormonal imbalance or due to drug effects. Needs a careful study and evaluation.

2. Congenital anomalies: 

Micro Penis: In this condition the penis is very small. An andrologists opinion and help are necessary.

Macropenis: The size is very big and common in some races.

Phymosis: The foreskin is too tight and cannot be retracted. Such cases need  surgical treatment through a procedure called circumcision.

Peyrone’s Syndrome: This condition occurring from childhood is caused by scarring on one of the two corpora cavornosa within the penis stunting its effectiveness during erection and makes the penis to bend almost 90 degrees in that direction. An andrological help and surgical correction is a must.

Hypospadias: In this condition the urinary meatus is under the glans and needs immediate surgical attention.

3. Sexually Transmitted diseases:

These include Gonorrhea, Syphilis, Yaws, Warts and AIDS. The last named one is beyond the scope for treatment where as the others can be tackled depending upon the extent of involvement. All of these are certainly preventable through safe sex by using condoms, avoiding unnatural sex acts, avoiding extramarital sex and avoid visiting prostitutes. One of the common and serious conditions resulting from STD’s is “Gonococcal stricture of the urethra” which may cause retention of urine and warrants medical and surgical interventions. Syphilitic canker is a very common condition affecting the glans penis where an ulcer is formed. 

4. Others:

Part of the male urethra, about an inch passes through a male sex gland called prostate and the rest of it passes through the penis. In cases where prostate gland is enlarged there occurs narrowing of the prostatic part of urethra and may even lead to retention of urine, if neglected.

Injuries may affect a penis: In some cases lack of knowledge in sexual act may lead to bleeding injuries due to a cut in the frenum. In rare cases a penis may get severed and needs immediate anostomosis if the severed portion can be saved.

Cancer Penis: Like in other organs cancer may affect a penis as well. Early recognition and surgical amputation of the penis with implantation of the urethra to the scrotun might save a patient though he is permanently bereft of any sex act.

Facts about Penis Sizes from Study Findings

  • § Though men are less sure of themselves regarding their penis size, 85% of women care less about it and were shown to be satisfied with the size and proportion of their partner's penis.

    § A study conducted on the issue of small or normal penis size, researchers found the following in a group of men:

    • Average penis size when flaccid is 8.8 cm (3.5 inches)
    • Average penis size when erect is 12.9 cm (5.1 inches)

    § Men who believed they had a small penis in a study was 45%.

    § The penis size in the flaccid state range around 7 to 10 centimeters (2.8-3.9 inches) across various studies

    § The length of erect penis ranges around 12 to 16 centimeters (4.7 to 6.3 inches).

    § Older age and higher BMI is weakly associated with a shorter erect penis length.

With increasing number of men seeking surgery to lengthen their penis, the Indian authors of a study say, that the definition of normal penile size was of "considerable interest" as there was a "steady increase in the number of people complaining of 'short penis' and seeking penile enlargement procedures."


*Disclaimer: This is not medical advice. The content is for educational purposes only. Please contact your doctor for any health care issues.