Anerection (clinically:penile erection orpenile tumescence) is aphysiological phenomenon in which thepenis becomes firm, engorged, and enlarged. Penile erection is the result of a complex interaction of psychological, neural, vascular, and endocrine factors, and is often associated withsexual arousal,sexual attraction orlibido, although erections can also be spontaneous. The shape, angle, and direction of an erection vary considerably between humans.
As an autonomic nervous system response, an erection may result from a variety of stimuli, includingsexual stimulation andsexual arousal, and is therefore not entirely under conscious control. Erections during sleep or upon waking up are known asnocturnal penile tumescence (NPT), also known as "morning wood". Absence of nocturnal erection is commonly used to distinguish between physical and psychological causes oferectile dysfunction andimpotence.
The state of a penis which is partly, but not fully, erect is sometimes known as semi-erection (clinically:partial tumescence); a penis which is not erect is typically referred to as being flaccid, or soft.
Physiology
Erection stages
Side views and comparison of the stages of both uncircumcised and circumcised human penis erection
An erection is necessary fornatural insemination as well as for the harvesting of sperm forartificial insemination, and is common for children and infants. After reachingpuberty, erections occur much more frequently.[1][2]An erection occurs when two tubular structures, called thecorpora cavernosa, that run the length of the penis, become engorged withvenous blood. This may result from any of variousphysiological stimuli, also known assexual stimulation andsexual arousal. Thecorpus spongiosum is a single tubular structure located just below the corpora cavernosa, which contains theurethra, through whichurine andsemen pass duringurination andejaculation respectively. This may also become slightly engorged with blood, but less so than the corpora cavernosa.
In some cases, the scrotum becomes tightened during an erection, and in most uncircumcised males, theforeskin automatically and gradually retracts throughout the various stages of erection, exposing theglans, though some individuals have to manually retract their foreskin.
Autonomic control
In the presence of mechanical stimulation, erection is initiated by theparasympathetic division of theautonomic nervous system with minimal input from thecentral nervous system. Parasympathetic branches extend from thesacral plexus into thearteries supplying the erectile tissue; upon stimulation, these nerve branches releaseacetylcholine, which in turn causes the release ofnitric oxide fromendothelial cells in thetrabecular arteries.[3] Nitric oxide diffuses to thesmooth muscle of the arteries (calledtrabecular smooth muscle[4]), acting as avasodilating agent.[5] The arteries dilate, filling thecorpus spongiosum andcorpora cavernosa with blood. Theischiocavernosus andbulbospongiosus muscles also compress the veins of the corpora cavernosa, limiting the venous drainage of blood.[6] Erection subsides when parasympathetic stimulation is discontinued; baseline stimulation from thesympathetic division of the autonomic nervous system causes constriction of thepenile arteries and cavernosal sinosoids, forcing blood out of the erectile tissue through erection-related veins which include one deep dorsal vein, a pair of cavernosal veins, and two pairs of para-arterial veins between Buck's fascia and the tunica albuginea.[7][8] Erection rigidity is mechanically controlled by reduction blood flow through theses veins, and thereby building up the pressure of the corpus cavernosum and corpus spongiosum, an integral instructure, the distal ligament, buttresses the glans penis.[9]
Afterejaculation or cessation of stimulation, erection usually subsides, but the time taken may vary depending on the length and thickness of the penis.[10]
Voluntary and involuntary control
Thecerebral cortex can initiate erection in the absence of direct mechanical stimulation (in response to visual, auditory, olfactory, imagined, or tactile stimuli) acting through erectile centers in the lumbar and sacral regions of thespinal cord.[11] The cortex may suppress erection, even in the presence of mechanical stimulation, as may other psychological, emotional, and environmental factors.[12]
The penis may become erect during sleep or be erect on waking up. Such an erection is medically known asnocturnal penile tumescence (informally:morning wood ormorning glory).[13][14][15][16]
Socio-sexual aspects
Social
Though an erection can have many causes, it is most commonly seen as an indicator ofsexual arousal and is therefore considered taboo or inappropriate for a public setting in many societies. This taboo is lesser than that surroundingpublic sex but higher than that surroundingnudity. Erectile dysfunction is often considered a flaw, eliciting shame in individuals affected.
Thepenile plethysmograph, which measures erections, has been used by some governments andcourts of law to measure sexual orientation. An unusual aversion to the erect penis is sometimes referred to asphallophobia.
Spontaneous or random erections
Erection visible beneath clothing
Spontaneous erections, also known as involuntary, random or unwanted erections, are commonplace and a normal part of male physiology. Socially, such erections can beembarrassing if they happen in public or when undesired.[1] Such erections can occur at any time of day, and if clothed may cause a bulge which (if required) can be disguised or hidden by wearing close-fitting underwear, a long shirt, or baggier clothes.[17]
The length of the flaccid penis is not indicative of the length of the penis when it becomes erect, with some smaller flaccid penises growing much longer, and some larger flaccid penises growing comparatively less.[18]Generally, the size of an erect penis is fixed throughout post-pubescent life. Its size may be increased by surgery.[19]
Though the size of a penis varies considerably between males, the average length of an erecthuman penis is 13.12 cm (5.17 inches), while the average circumference of an erect human penis is 11.66 cm (4.59 inches).[20]
Direction
Although many erect penises point upwards, it is common and normal for the erect penis to point nearly vertically upwards or horizontally straight forward or even nearly vertically downwards, all depending on the tension of the suspensory ligament that holds it in position. An erect penis can also take on a number of different shapes, ranging from a straight tube to a tube with a curvature up or down or to the left or right. An increase in penile curvature can be caused byPeyronie's disease. This may cause physical and psychological effects for the affected individual, which could includeerectile dysfunction or pain during an erection. Treatments include oral medication (such ascolchicine) or surgery, which is most often performed only as a last resort.The following table shows how common various erection angles are for a standing male. In the table, zero degrees (0°) is pointing straight up against the abdomen, 90° is horizontal and pointing straight forward, and 180° is pointing straight down to the feet. An upward pointing angle is most common and the average erection angle is 74.3 degrees. The penile curvature was measured same time. 63% men have straight penis. 22.2% men have upwards curvature and 14.8% men have downwards curvature.[21]
Erectile dysfunction (also known as ED or "(male) impotence") is asexual dysfunction characterized by the inability to develop and/or maintain an erection.[22][23] The study of erectile dysfunction within medicine is known asandrology, a sub-field withinurology.[24]
Erectile dysfunction may occur due tophysiological orpsychological reasons, most of which are amenable to treatment. Common physiological reasons include diabetes, kidney disease, chronic alcoholism, multiple sclerosis, atherosclerosis, vascular disease, including arterial insufficiency and venogenic erectile dysfunction,[25] and neurologic disease which collectively account for about 70% of ED cases.[5] Some drugs used to treat other conditions, such aslithium andparoxetine, may cause erectile dysfunction.[23][26]
Erectile dysfunction, tied closely as it is to cultural notions ofpotency,success andmasculinity, can have devastating psychological consequences including feelings ofshame,loss or inadequacy.[27] There is a strongculture of silence and inability to discuss the matter. Around one in ten men experience recurring impotence problems at some point in their lives.[28]
Priapism
Priapism is a painful condition in which the penis does not return to its flaccid state, despite the absence of both physical and psychological stimulation. Priapism lasting over four hours is a medical emergency.
Hard flaccid syndrome
Hard flaccid syndrome is a rare, chronic condition characterized by a flaccid penis that remains in a firm, semi-rigid or semi-erect state in the absence of sexual arousal.
At the time of penetration, thecanine penis is not erect, and only able to penetrate the female because it includes a narrow bone called thebaculum, a feature of mostplacental mammals. After the male achieves penetration, he will often hold the female tighter and thrust faster, and it is during this time that the male's penis expands, unlike human sexual intercourse, where the male penis commonly becomes erect before entering the female.[29]
An elephant's penis is S-shaped when fully erect and has a Y-shapedorifice.[30]
Given the small amount of erectile tissue in abull's penis, there is little enlargement after erection. The penis is quite rigid when non-erect, and becomes even more rigid during erection. Protrusion is not affected much by erection, but more by relaxation of theretractor penis muscle and straightening of the sigmoid flexure.[31][32]
A malefossa's penis reaches to between his forelegs when erect.[33]
When not erect, ahorse's penis is housed within the prepuce, 50 centimetres (20 in) long and 2.5 to 6 centimetres (0.98 to 2.36 in) in diameter with the distal end 15 to 20 centimetres (5.9 to 7.9 in). Theretractor muscle contracts to retract the penis into the sheath and relaxes to allow the penis to extend from the sheath.[34] When erect, the penis doubles in length[35] and thickness and theglans increases by 3 to4 times.[34] Erection and protrusion take place gradually, by the increasingtumescence of the erectile vascular tissue in thecorpus cavernosum penis.[36][37] Most stallions achieve erection within 2 minutes of contact with an estrus mare, and mount the estrus mare 5–10 seconds afterward.[38]
Abird penis is different in structure frommammal penises, being an erectile expansion of the cloacal wall and being erected bylymph, not blood.[39] The penis of thelake duck can reach about the same length as the animal himself when fully erect, but more commonly is about half the bird's length.[40][41]
Clinically, erection is often known as "penile erection", and the state of being erect, and process of erection, are described as "tumescence" or "penile tumescence". The term for the subsiding or cessation of an erection is "detumescence".
Colloquially and inslang, erection is known by many informal terms. Commonly encounteredEnglish terms include 'stiffy', 'hard-on', 'boner' and 'woody'.[42] There are several slang words, euphemisms and synonyms for an erection in English and in other languages (see also:The WikiSaurus entry).
^Li CY, Kayes O, Kell PD, Christopher N, Minhas S, Ralph DJ (2006). "Penile suspensory ligament division for penile augmentation: indications and results".Eur. Urol.49 (4):729–733.doi:10.1016/j.eururo.2006.01.020.PMID16473458.
^Milsten, Richard (et al.), The Sexual Male. Problems And Solutions. London, 2000. (ISBN0-393-32127-4)
^abSadeghipour H, Ghasemi M, Ebrahimi F, Dehpour AR (2007). "Effect of lithium on endothelium-dependent and neurogenic relaxation of rat corpus cavernosum: role of nitric oxide pathway".Nitric Oxide.16 (1):54–63.doi:10.1016/j.niox.2006.05.004.PMID16828320.
^Williams, Warwick, It's Up To You: Overcoming Erection Problems. London, 1989. (ISBN0-7225-1915-X)
.jpg)
_na_sajmu_MESAP_2015.jpg)
.svg)
