Penis

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Innervated by autonomic and somatic nervous systems.

Somatic innervation comes from S2-S4 sacral nerve roots via the pudendal nerve.

Sexual stimulus releases nitric oxide from the terminal ends of the cavernosal nerves.

An external male organ that serves as the urinal duct.

Its main parts are the root, the body, and the epithelium of the penis including the shaft skin and the foreskin covering the glans penis.

The body of the penis is made up of three columns of tissue: two corpora cavernosa on the dorsal side and corpus spongiosum between them on the ventral side.

The urethra passes through the prostate gland, where it is joined by the ejaculatory duct, and then through the penis.

The urethra traverses the corpus spongiosum, and it opens at the meatus, which lies on the tip of the glans penis.

The urethra Is a passage for urination and ejaculation of semen.

The penis develops from the same tissue in the embryo as does the clitoris in females.

The skin around the penis and the urethra come from the same embryonic tissue from which develops the labia minora in females.

The stiffening and rising of the penis is an erection, which occurs during sexual arousal.

Erections can occur in non-sexual situations, frequently occur during adolescence and sleep.

The glans of the penis is darker in color, and covered by the foreskin, if present.

In its fully erect state, the shaft of the penis is rigid, with the skin tightly stretched.

The erect penis may be straight, and point at an upward or downward, straight ahead, and may also have a tendency to the left or right.

The average erect human penis is approximately 5.1–5.9 inches in length with 95% of adult males within 4.2–7.5 inches.

Erect-penis size varies between 3.8 and 6.3 in.

The longest documented penis was 13.5 in long and 6.26 around.

This difference in react penis size may be caused by genetics but also by environmental factors such as fertility medications, culture, diet, and chemical/pollution exposure.

Neither age nor size of the flaccid penis accurately predicts erectile length.

The most common form of genital alteration is circumcision.

The root of the penis is the radix.

The radix is the attached part of the penis, consisting of the bulb of penis in the middle and the crus of penis, one on either side of the bulb.

The body of the penis has two surfaces: dorsal-posterosuperior in the erect penis, and ventral or urethral-facing downwards and backwards in the flaccid penis.

Epithelium of the penis consists of the shaft skin, the foreskin, and the preputial mucosa on the inside of the foreskin and covering the glans penis.

The penis is made up of three columns of tissue: two corpora cavernosa lie next to each other on the dorsal side and one corpus spongiosum lies between them on the ventral side.

The enlarged and bulbous-shaped end of the corpus spongiosum forms the glans penis.

The glans penis supports the foreskin, or prepuce.

The foreskin is a loose fold of skin that in adults can retract to expose the glans.

The area on the underside of the penis, where

The foreskin is attached at the the frenum, the underside of the penis.

The rounded base of the glans is called the corona.

The perineal raphe is the noticeable line along the underside of the penis.

The urethra, the last part of the urinary tract, traverses the corpus spongiosum.

The urethral opening, is known as the meatus, and it lies on the tip of the glans penis.

The urethra is a passage both for urine and for the ejaculation of semen.

The raphe is the visible ridge between the lateral halves of the penis, found on the ventral or underside of the penis.

The raphe runs from the meatus across the scrotum to the perineum.

Pearly penile papules are raised bumps of somewhat paler color around the base of the glans which typically develop in men aged 20 to 40.

Pearly penile papule incidence ranges from 8 to 48 percent of all men.

Pearly penile papules are not harmful or infectious and do not require treatment.

Fordyce’s spots are small, raised, yellowish-white spots 1–2 mm in diameter that may appear on the penis.

Fordyce’s spots are common and not infectious.

Sebaceous prominences are raised bumps similar to Fordyce’s spots on the shaft of the penis, and are normal.

Phimosis refers to the inability to retract the foreskin fully.

Phimosis is normal and harmless in infancy and pre-pubescence, occurring in about 8% of boys at age 10.

Curvature of the penis seen in all directions, with straight penises being uncommon..

Curvature of the penis rarely inhibits sexual intercourse.

Curvature as great as 30° is considered normal.

Medical treatment is rarely considered unless the angle of curvature exceeds 45°.

Changes to the curvature of a penis may be caused by Peyronie’s disease. Development

In the developing fetus, the genital tubercle develops into the glans of the penis in males and into the clitoral glans in females.

With puberty, the penis, scrotum and testicles will enlarge toward maturity.

Penile growth is typically complete not later than age 17, and possibly earlier.

The urethra drains urine from the bladder through the prostate gland where it is joined by the ejaculatory duct, and then onward to be expelled through the penis.

The external sphincter, lies at the root of the penis, near the proximal end of the corpus spongiosum.

The external sphincter, a striated muscle that is under voluntary control, relaxes the urethral sphincter allowing urine in the upper urethra to enter the penis emptying the bladder.

Urination involves coordination between the central, autonomic, and somatic nervous systems.

Urination may occur as an involuntary reflex in infants, the elderly an in patients with neurological impairment.

Centers in the brain that regulate urination include the pontine micturition center, periaqueductal gray, and the cerebral cortex.

During an erection, these brain centers block the relaxation of the sphincter muscles, acting as a physiological separation of the excretory and reproductive function of the penis, and preventing urine from entering the upper portion of the urethra during ejaculation.

The distal section of the urethra allows a human male to direct the stream of urine

Holding the penis allows the male to choose the posture in which to urinate, and the pref2241ed position may be influenced by cultural or religious beliefs.

An erection refers to the stiffening and rising of the penis, which occurs during sexual arousal.

Erections can also occur in non-sexual situations, due to friction with clothing, a full bladder or large intestine, hormone fluctuations, nervousness, and undressing.

Erections normally occur during sleep and upon waking.

Erections are due to the the autonomic dilation of arteries supplying blood to the penis, which allows more blood to fill the three spongy erectile tissue chambers in the penis

Blood filling the erectile tissue causes the penis to lengthen and stiffen.

The engorged erectile tissue constricts the veins that carry blood away from the penis.

When an equilibrium is reached where an equal volume of blood flows into the dilated arteries and out of the constricted veins a sustained erectile size is achieved.

The scrotum tightens during erection.

The direction the erect penises points to depends on the tension of the suspensory ligament that holds it in position.

Ejaculation refers to the ejecting of semen from the penis.

Ejaculation is usually accompanied by orgasm.

During ejaculation a series of muscular contractions delivers semen, containing male spermatozoa from the penis.

Ejaculation is usually the result of sexual stimulation, which may include prostate stimulation.

Ejaculation may occur spontaneously during sleep, ref2241ed to as a nocturnal emission or wet dream.

For men who can not ejaculate the term anejaculation is used.

Ejaculation has two phases: emission and ejaculation proper.

The emission phase of the ejaculatory reflex is under control of the sympathetic nervous system.

The ejaculatory phase is under control of a spinal reflex at the level of the spinal nerves S2–4 via the pudendal nerve.

Following ejaculation a refractory period occurs.

The sperm count in ejaculations is decreased if copulation occurs more than 3 to 5 times in a week.

Ejaculates can travel up to 30-60 centimeters at a time, allowing its placement at the highest point of the vaginal tract, increasing the chances that an egg will be fertilized.

The number of sperm in any given ejaculate varies from one ejaculate to another.

Males also adjust their ejaculates in response to sperm competition in terms of amount and quality.

Female attractiveness has been shown to be an indicator of sperm quality, with greater value in women so perceived.

Males produce larger ejaculates containing better, more motile sperm when mating with perceived attractiveness to them.

Paraphimosis refers to the inability to move the foreskin forward over the glans.

In Peyronie’s disease, scar tissue grows in the soft tissue of the penis, causing curvature.

Penile thrombosis can occur during periods of frequent and prolonged sexual activity, especially with fellatio.

Infection with the herpes virus can occur after sexual contact and may lead to the development of herpetic lesions.

Pudendal nerve entrapment refers to a a condition characterized by pain on sitting and the loss of penile sensation and orgasm.

Pudendal nerve entrapment can occur by being damaged by narrow, hard bicycle seats and accidents.