Mechanism of erection

Mechanism of erection

What is an erection?

An erection is a phenomenon in which a man’s penis becomes large and stiff due to sexual arousal and sexual stimulation.
You may also unknowingly get an erection.

An erection is a phenomenon that has been seen since infancy, and the penis of an infant may erect when changing diapers or taking a bath.
Infants’ erections are caused by reflexes to physical stimuli such as touching, rubbing when undressing, or touching cold air.

Even as an adult, you may have a reflexive erection in response to such physical stimuli.
This leads to an unconscious erection.

Normally, the penis is flexible and hangs from the man’s crotch.
When it becomes erected, it becomes ” thick “, ” long “, and ” hard “, and by protruding forward and upward, it can be inserted into the female genitals during sexual activity.

Originally, an erection is a physiological phenomenon necessary for the reproductive act of inserting the penis into the vagina of the female genitalia and leaving offspring for the purpose of pregnancy and childbirth.
However, it is also a necessary phenomenon for communication or sexual activity to obtain sexual pleasure between the opposite sex and the same sex.

By the way, the length of the penis at the time of erection in Japanese is said to be about 13 cm as a statistical average value.

Mechanism of erection

What is an erection

I will explain the mechanism of how an erection occurs and ends.

Normally, the condition of the penis is that blood flows from the deep artery of the penis and the helicine arteries into the corpus cavernosum, and the same amount of blood returns to the body through veins.
Therefore, the penis does not become stiff and can remain soft.

When an erection occurs, when a man feels sexual arousal or sexual stimulation, the brain issues an erection command to the penis through the erectile nerves.
Then, the activity of vascular endothelial cells in the corpus cavernosum of the penis becomes active, and NO (Nitric oxide) is produced and diffused in smooth muscle.
NO activates an enzyme called soluble guanylate cyclase and increases a vasodilator called cGMP (Cyclic guanosine monophosphate) in the blood vessels.

This substance, cGMP, relaxes the smooth muscles of the corpus cavernosum penis and widens the blood vessels of the deep artery of the penis, increasing blood flow and promoting erection.

As blood flows into the corpus cavernosum, the sponge-like corpus cavernosum expands and the hard membrane called the tunica albugi also expands.
The soft veins are sandwiched between the dilated corpus cavernosum and the hard thin film, which is compressed and contracts, preventing blood from bleeding from the veins.

In this way, blood accumulates more and more in the corpus cavernosum penis, eventually resulting in an erection.

In other words, an erection is a phenomenon of contraction and relaxation of the smooth muscles of the corpus cavernosum penis and can be thought of as looking at changes in blood circulation occurring in blood vessels.

The erection ends after ejaculation or after sexual arousal has subsided.

To prevent the penis from becoming erected all the time, there is an enzyme in the human body that suppresses erection, PDE5 (phosphodiesterase 5).
The vasodilator cGMP is broken down by an enzyme called PDE5, which ends the erection.

As sexual arousal subsides and PDE5 degrades and diminishes cGMP, the blood vessels that were widened by cGMP begin to contract again, and the filled corpus cavernosum blood returns to the body.
When a certain amount of blood escapes from the corpus cavernosum, the penis becomes soft and normal.

Flow to erection

Sexual arousal and sexual stimulation are received by all five senses of ” sight, ” ” hearing, ” ” smell, ” ” tactile, ” and ” taste .”
Information on sexual arousal and sexual stimulation received by the five senses is transmitted to the brain.

The brain that has been sexually aroused or stimulated has increased libido.
The brain issues an erection command as a reaction to libido.
Erection commands from the brain are transmitted in the order of “brain-> spinal cord-> erectile nerve-> penis”.
In other words, it can be said that the “brain and penis” are connected by the “spinal cord and erectile nerve”.

When the penis receives an erection command from the brain, the smooth muscle near the penis relaxes.

The penis is made up of a sponge-like organ called the corpus cavernosum.
Just as water collects in a sponge wrapped in vinyl, it becomes large and hard, and blood in the corpus cavernosum makes it large and hard.

In the non-erection state, the blood vessels connected to the corpus cavernosum of the penis are in a contracted state due to smooth muscles, etc., so almost no blood flows through the penis.

When an erection command is transmitted from the brain to the erectile nerve, smooth muscles loosen and blood vessels expand, a large amount of blood flows into the corpus cavernosum, and the penis becomes swollen.

This is the flow leading up to the ” erection “.

For normal erection, nerves that deliver sexual arousal and sexual stimulation from the brain to the penis, NO production, activation of soluble guanylate cyclase, increased cGMP, relaxation of smooth muscle and penile arteries, veins Various functions such as pressure on the penis need to be performed systematically.

If a problem occurs at any of these stages (1) to (4), you will not be able to get a sufficient erection and the risk of ED will increase.

What is the nocturnal erection phenomenon (morning standing)?

Nocturnal penile tumescence (NPT) is called nocturnal penile tumescence (NPT) in medical terms.
Strictly speaking, morning standing and nocturnal erection have different meanings.
The morning rise and nocturnal erection phenomenon is a phenomenon in which an erection occurs unconsciously even though you are not sexually aroused or sexually stimulated.

Normally, a person repeats light sleep REM sleep and deep sleep non- REM sleep during sleep.
During sleep, REM sleep and non-REM sleep alternate approximately every 90 minutes.

REM sleep is said to be a dream-friendly sleep, and erections may occur during this REM sleep.
During REM sleep, your body is resting, but your brain is working.
Therefore, during REM sleep, breathing, pulse, blood pressure, etc. become high, and the flow may cause an erection.

This is the nocturnal erection phenomenon (nocturnal sleep erection phenomenon).

It is thought that the morning rise is caused by the same mechanism.
It is said that people often wake up from REM sleep because REM sleep gradually extends in the morning.
Then, when an erection is observed just before waking up, it becomes a morning rise.

Therefore, morning standing is considered part of the nocturnal erection phenomenon.

But don’t worry too much if you don’t have a morning rise, as it doesn’t always happen every morning.
Basically, it is said that if you wake up from non-rem sleep, you will not be allowed to stand up in the morning, but as you get older, you may get an erection during non-rem sleep.

In addition, you may have sexual dreams while sleeping, and if it overlaps with the nocturnal erection phenomenon, you may end up with nocturnal emission (nocturnal emission) .
Nocturnal emission is one of the physiological phenomena often seen in adolescent men by ejaculating by having sexual dreams while sleeping.
No special treatment is required unless you are dreaming of something morbid.

Erection is a male health barometer

An erection is an important barometer for knowing a man’s health.
This is because an erection cannot be established unless the nerves and blood vessels are healthy.

ED (erectile dysfunction) is a disease of nerves and blood vessels.

Due to arteriosclerosis, blood vessels may become clogged, making it impossible to get an erection.
In addition, diabetes may cause nerve damage, resulting in ED.

In addition, if you are under mental stress, your nerves may not work well and you may not be able to get an erection.
Therefore, a comfortable erection is an evidence that your nerves, blood vessels, and mental health are all in good condition.

Conversely, when erectile dysfunction is not possible, ED may be suspected and one or all of the nerves, blood vessels, and mental illness may be upset.

Erection hardness is proportional to erection angle

When having sexual intercourse with a woman, it is convenient for the penis at the time of erection to be facing upward rather than horizontally due to the angle with the female genitalia (vagina, uterine ostium, etc.).

The angle of the erection is very important, and if the penis is warped upwards, it will be easier to stimulate the erogenous zone of the female genitals.
In addition, the glans penis hits the anterior wall of the vagina and is easily guided downward, so the stimulation tends to increase and the erection can be prolonged.

However, as aging gradually loses erection power, the angle of erection decreases with age.

There is an easy way to know the average erection angle for each age.

Open the palm fully while keeping the side of the ring finger on the little finger side horizontal to the ground.
Based on the ring finger, the angle of the erection decreases with age, such as the angle of the thumb in the teens, the angle of the index finger in the 20s, the angle of the middle finger in the 30s, and so on.

If erection force = erection hardness, it can be said that erection hardness is proportional to erection angle.

The mechanism that ED therapeutic drugs works

ED therapeutic drug

When men feel sexual stimulation, the vasodilator cGMP increases in the blood vessels.
This substance, cGMP, relaxes the smooth muscles of the corpus cavernosum penis, widens the blood vessels in the penis, and increases blood flow, thus promoting erection.

At the same time, there is an erection-suppressing enzyme, PDE5, in the human body to prevent the penis from constantly erecting.
The vasodilator cGMP is broken down by an enzyme called PDE5, which ends the erection.

Most ED patients are unable or unable to have an erection because this PDE5 is overworked.

The active ingredient in ED treatments such as Viagra can block the action of an enzyme called PDE5 that suppresses this erection.
If PDE5 is weakened, cGMP will work normally without being degraded and the erection will be promoted.

Because of this effect, ED treatments such as Viagra are also called PDE5 inhibitors.

By the way, there are three main active ingredients of ED treatment drugs that have the effect of inhibiting the action of the enzyme PDE5: sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis).

Relationship between erection and ED treatment

situationPresence or absence of an erection command from the brainEnzyme (PDE5) statusPresence or absence of erection
Normal timenoneDominancenone
Normal erectionYes (reaches the penis)Inferiordo
ED patients
(no ED treatment)
Yes (reaches the penis)Dominance (for some reason)do not
ED patients
(with ED treatment)
Yes (reaches the penis)Inferiority (effect of active ingredient)do

How to find out about your erectile function, etc.

If you are concerned about ED, find out about your erectile function.

We would like to introduce some ED self-check tools that can easily explore the possibilities of ED.

Erection hardness score “EHS”

The Erection Hardness Score (EHS) is an evaluation tool developed in the United States in 2007 that allows you to easily check whether or not you have ED.
It can be judged in 5 stages from grade 0 to grade 4.
Highly reliable, based on the US version in 2009, erection hardness score (Japanese version EHS) was developed based on the US version.

For many who are suspected of having ED, the erection hardness score (Japanese version of EHS) is short, easy to use, and attractive.
With just one question, men can easily assess the hardness of an erection and report it to their doctor.

The Erection Hardness Score (Japanese version of EHS) answers the question ” How do you evaluate your erection hardness? ” With the following grades.

Erection hardness score (Japanese version EHS)

gradeGrade 0Grade 1Grade 2Grade 3Grade 4
Image of hardnessCross markKonjacKonjacMandarin orangeMandarin orangegrapefruitgrapefruitappleapple
Erection state of the penisThe penis does not grow.The penis grows, but it is not stiff.The penis is stiff, but not enough for insertion.The penis is stiff enough for insertion, but not completely stiff.The penis is completely stiff and stiff.

* The image of hardness is just an image of the hardness score of erection (Japanese version EHS).
* The result of the hardness score of erection (Japanese version EHS) is just a guideline for suspicion of ED.

If your answer falls between Grade 0 and Grade 2, you are very likely to have ED, and if you do not have satisfactory sexual activity even with Grade 3, you will be suspected of having ED.

International erectile function score “IIEF5”

The International Index of Erectile Function (IIEF) is used for screening tests for ED (erectile dysfunction) and for determining the therapeutic effect.
Also known as the shortened version of the Japanese translation, ” IIEF5 “.

For the International Erectile Function Score (IIEF5) , select from the following answers to the content ” Please select the applicable one in the past 6 months. (5 questions in total) “.

International Erectile Function Score (IIEF5)

1. How confident were you to get an erection and maintain it?

  • ・ Very low (1 point)
  • ・ Low (2 points)
  • ・ Medium (3 points)
  • ・ High (4 points)
  • ・ Very high (5 points)

2. How often did you get the hardness to insert when you got an erection due to sexual stimulation?

  • ・ Almost or not at all (1 point)
  • ・ Occasionally (much less frequently than half) (2 points)
  • ・ Occasionally (almost half the frequency) (3 points)
  • ・ Frequently (much more frequently than half) (4 points)
  • ・ Almost always or always (5 points)

3. How often did you maintain an erection during sexual intercourse after insertion?

  • ・ Almost or not maintained at all (1 point)
  • ・ Occasionally maintained (much less frequently than half) (2 points)
  • ・ Occasionally maintained (almost half the frequency) (3 points)
  • ・ Frequently maintained (much more frequently than half) (4 points)
  • ・ Almost always or always maintained (5 points)

4. During sexual intercourse, how difficult was it to maintain an erection until the end of sexual intercourse?

  • ・ It was extremely difficult (1 point)
  • ・ It was very difficult (2 points)
  • ・ It was difficult (3 points)
  • ・ It was a little difficult (4 points)
  • ・ It was not difficult (5 points)

5. How often were you satisfied with your sexual intercourse when you tried it?

  • ・ I was almost or not satisfied at all (1 point)
  • ・ Occasionally satisfied (much less than half frequency) (2 points)
  • ・ Sometimes I was satisfied (almost half the frequency) (3 points)
  • ・ Often satisfied (much more frequently than half) (4 points)
  • ・ Almost always or always satisfied (5 points)

* This questionnaire is created based on the International Erectile Dysfunction Score (IIEF5), which is used as an auxiliary material when conducting ED examinations at medical institutions.

The result is derived from the total score of each answer.
The contents of the diagnosis result are as follows.

Classification of “IIEF5” severity

  • 22 to 25 points: Normal
  • 17 to 21 points: Mild ED
  • 12 to 16 points: Mild to moderate ED
  • 8 to 11 points: Moderate ED
  • 5 to 7 points: Severe ED

* The result of the International Erectile Dysfunction Score (IIEF5) is just a guideline for suspicion of ED.

Those with a total score of 21 or less are suspected of having ED.
If you have any symptoms of concern, please consult your doctor once.

Diseases related to erection other than ED

Diseases related to erection other than ED

There are other erection-related diseases besides ED.

There are some diseases that can lead to ED, so keep this in mind for reference.


Priapism is a disease in which an erection continues regardless of one’s will or sexual desire.
A normal erection returns when you stop sexually imagining or have no sexual stimulation, but with priapism, the erection does not stop.

Persistent erection is arterial persistent erection in which the arteries of the corpus cavernosum of the penis are torn for some reason and blood continues to flow excessively. I have an erection.

In arterial priapism, the penis is incompletely stiff and painless, whereas, in venous priapism, the penis is stiff and painful.
In venous priapism, if left untreated, blood flow is stopped, so fresh oxygen is not sent, and tissues such as the corpus cavernosum of the penis begin to die about 6 hours after the onset.
Severe tissue damage can also permanently impair erectile function.

People with sickle cell disease with chronic anemia, multiple myeloma, also called blood cancer, and leukemia, are more likely to affect the blood flow in the penis and are at high risk of developing a persistent erection. increase.

It is the most common disease in boys aged 5 to 10 and men in their 20s and 50s.

As persistent erection worsens, the chances of getting ED to increase, so early treatment is needed.

Penile induration (Peyronie’s disease)

Peyronie’s disease (Peyronie’s disease) is a disease in which the fibrous tunica albugi that surrounds the corpus cavernosum of the penis becomes inflamed and forms a hard lump.

The lump does not stretch normally when it erects, causing great distortion of the penis from the lump, making sexual activity difficult or impossible.
In addition, it can be painful at the time of erection, and when it gets worse, it can cause ED.

Trauma can cause Peyronie’s disease, but it can occur without trauma.
In the absence of trauma, diabetes, high blood pressure, and smoking cigarettes are considered risk factors for the onset.

If left untreated, the chances of getting ED to increase, so early treatment is needed.


Paraphimosis is a condition in which the foreskin tightens the lower part of the glans when the foreskin is peeled off from the state of the foreskin to expose the glans, and the foreskin that has been turned over cannot be restored.

If the foreskin that has turned up cannot be restored, the pressure increases and the glands swell, and if left untreated, the tissue of the penis may become necrotic. It can be very painful.

It affects only men with pseudo phimosis or true phimosis who have not undergone circular resection of the foreskin.
It can occur after medical procedures (such as inserting a catheter into the urethra) or after cleaning the child’s penis and leaving the foreskin turned over.

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