The penis is the male sex organ, reaching its full size during puberty. In addition to its sexual function, the penis acts as a conduit for urine to leave the body.
The internal structure of the penis consists of two cylinder-shaped vascular tissue bodies (corpora cavernosa) that run throughout the penis; the urethra (tube for expelling urine and ejaculate); erectile tissue surrounding the urethra; two main arteries; and several veins and nerves. The longest part of the penis is the shaft, at the end of which is the head, or glans penis.
When a man becomes sexually excited, the nerves surrounding his penis become active, causing the muscles around the arteries to relax and more blood to flow into the penis. The sponge like material then absorbs the additional blood, making the penis stiff and hard, or erect. This erection tightens the veins so the blood can’t leave the penis, enabling the penis to remain erect. After a man ejaculates or if his arousal fades, detumescence occurs, in which the brain sends a signal to allow the blood to leave the erect penis, and it returns to its flaccid state.
Penis anatomy is remarkably complex. Following is the definitions for the most important parts.
1. The Corpora Cavernosa. The corpora cavernosa are two chambers that fill most of the penis. The chambers are filled with a spongy tissue that includes muscles, open spaces, veins and arteries. An erection occurs when the corpora cavernosa become engorged with blood and expand.
2. The Tunica Albuginea. A membrane called the tunica albuginea surrounds the corpora cavenosa. This membrane helps keep blood in the penis during an erection.
3. Urethra. The urethra is the tube through which urine travels. Ejaculate also travels through the urethra. It runs down the underside of the penis, beneath the corpora cavernosa and widens at its opening, called the meatus. The meatus is located at the glans (the head of the penis).
4. Corpus Spongiosum. The corpus spongiosum is a chamber that surrounds the urethra. It becomes engorged with blood during an erection.
5. The Prostate. The prostate is a small gland located in the pelvis. It surrounds the urethra and plays an important role in ejaculation. Sperm, which is produced in the testicles and stored in the seminal vesicles, is mixed with prostatic fluid and secretions from the bulbourethral gland to form semen. During ejaculation, semen is expelled through the urethra from the ejaculatory ducts.
6. Glans (head) of the penis. In uncircumcised men, the glans is covered with pink, moist tissue called mucosa. Covering the glans is the foreskin (prepuce). In circumcised men, the foreskin is surgically removed and the mucosa on the glans transforms into dry skin. The glans serves several purposes: increasing the chances for fertilization of an egg, creating extra friction during sex, and acting as a shock absorber within the vagina during intercourse.
7. Corona. The 'crown,' a ridge of flesh demarcating where the head of the penis and the shaft join.
8. Frenulum, Frenum. A thin strip of flesh on the underside of the penis that connects the shaft to the head.
9. Smegma. A substance with the texture of cheese secreted by glands on each side of the frenulum in uncircumsized men.
10. Scrotum. The scrotum is a sac that hangs behind and below the penis, and contains the testes (testicles), the male sexual glands. The scrotum's primary function is to maintain the testes at approximately 34 C, the temperature at which the testes most effectively produce sperm.
11. Testes, Testicles. The male sexual glands, the two testes within the scrotum produce sperm and testosterone. Within each testis is a kilometer of ducts called the seminiferous tubules, the organs which generate sperm. Each testicle produces nearly 150 million sperm every 24 hours.
12. Epididymis. The epididymis is a 'holding pen' where sperm produced by the seminiferous tubules mature. The sperm wait here until ejaculation or nocturnal emission.
13. Vas Deferens. The ducts leading from the epididymis to the seminal vesicles. These are the ducts that are cut during the procedure known as vasectomy.
14. Seminal Vesicles. The seminal vesicles produce semen, a fluid that activates and protects the sperm after it has left the penis during ejaculation
15. Prostate Gland. Also produces a fluid that makes up the semen. The prostate gland also squeezes shut the urethral duct to the bladder, thus preventing urine from mixing with the semen and disturbing the pH balance required by sperm.
17. Cowper's Glands. The Cowper's glands secrete a small amount of pre-ejaculate fluid prior to orgasm. This fluid neutralizes the acidity within the urethra itself.
What's the average size of the penis?
In European medical literature, the average penis length is between 7.5 cm and 10.2 cm, with a diameter of 3.2 cm. Erect, a penis will usually be between 12 cm and 17 cm long and nearly 4 cm thick. Length when erect is not proportionate to length when flaccid. According to Mandens Krop, the average is 15 cm and 90% are between 13 cm and 18 cm. However, there are medical records for fully functional penises from 1.5 cm to 30 cm in length.
In American medical literature, the average penis length is between 5.1 and 5.7 inches (based on the data provided by Alfred C. Kinsley Institute).
If you still think, after all these years and sexual experience, that the penis size is too important, think about the fact that the normal vagina is only eight to thirteen centimeters long, and even a small penis can touch every square centimeter within the vagina.
What’s about erection angle?
The direction the erect penis points depends on anatomy and is not related to penile rigidity or firmness. The majority point upwards or straight out, but a sizeable minority just point downwards. There is no medical information that women prefer one over the other. The variation in the angle depends on the size and tension of the ligaments holding the base of the penis. If they are tight, the penis will point up, if not then it points down. When it loosens, the support drops and the erection angle becomes less which typically happens with age.
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