What causes an erection?

woman-sittingErection of the penis is one of the most important biological, physiological and reproductive phenomena in all human males regardless of their age, genetic make-up or geographic location. While the word “penile erection” is frequently associated with “sexual” meanings, erection usually & regularly occurs without sexual excitement and on daily basis. The average male has four to eight spontaneous erections every night while he sleeps. They usually occur when dreaming.

Understanding the causes of erection

In the case of your penis, there are actually two tasks that it handles:

  • Releasing urine from the bladder, known as urination
  • Releasing sperm and seminal fluid from the prostate gland, known as ejaculation

When things are working properly, ejaculation is a three-step process:

  • Arousal: The man becomes sexually aroused
  • Erection: The penis responds by becoming erect
  • Ejaculation: Physical stimulation of the penis causes ejaculation

If, by any chance, step two (erection) does not happen, the step three (ejaculation) becomes difficult or impossible and the condition is called “male impotence”. It means, even if the man is stimulated, the penis does not become erect. To understand why, you need to understand the mechanism of an erection.

When you want to move nearly any part of your body, you do it using muscles. Whether you are moving your fingers, toes, arms or legs, muscles do the work. Even when you stick your tongue out, you do it using muscles:

  • You think about moving some part of your body
  • The appropriate muscles contract
  • That part of the body moves

Muscles let you move your body voluntarily with precise control. The penis, on the other hand, is completely different. There are no muscluar contractions involved in making the penis erect. To become erect, the penis instead uses pressure. Probably the easiest way to understand how the penis becomes erect is to think about a balloon. If a balloon has no air in it, it's limp. As you inflate a limp balloon with just a little air, it becomes elongated and rigid.

Role of corpora cavernosa in causing erection

The penis uses a similar mechanism, but instead of using pressurized air to become rigid, the penis uses pressurized blood. The penis contains two cigar-shaped structures, called corpora cavernosa (singular: corpus cavernosum), that it uses to become erect.

You can think of the corpora cavernosa as balloon-like tubes. Arteries bring blood into these two tubes, and veins carry blood away from them. The penis can be either limp or erect, depending on the flow of blood:

In a non-erect state, the arteries that bring blood into the corpora cavernosa are somewhat constricted, while the veins that drain the blood from the penis are open. There is no way for pressure to build inside the penis. In this state, the penis is limp.

When a man becomes aroused, the arteries leading into the penis open up so that pressurized blood can enter the penis quickly. The veins leaving the penis constrict. Pressurized blood is trapped in the corpora cavernosa, and this blood causes the penis to elongate and stiffen. The penis is erect.

If the arteries leading to the penis do not open up properly, it is difficult or impossible for a man to become erect. This problem is the leading cause of erectile dysfunction (ED).

To solve an erection problem when the cause is poor blood flow, you need to open the arteries

Understanding blood flow through the penis

To understand the vital role of blood in causing the erection of your penis, you must think about the way blood flows in your body. Your body has just one pump, the heart. But different parts of the body need different amounts of blood at different times.

For example:

  • If you eat a big meal, your body needs to send more blood to the stomach and intestines to help with digestion.
  • If you are running in a marathon, your body needs to send more blood to your arm and leg muscles, and it may want to cut most of the blood flowing to the stomach (and other nonessential organs) in order to save oxygen for the legs

What your body needs, in other words, is a set of valves that it can use to increase and decrease blood flow to certain parts of the body. And your brain needs a way to control those valves so it can turn them on and off when necessary.

Role of the brain in causing an erection

The penis is one of the places in the body where the brain needs to be able to turn the blood flow on and off with a valve.  When a man is sexually stimulated by sight, thought, or touch, the brain sends signals that relax the smooth muscles around the arteries that supply blood to the corpora cavernosa. The veins draining the bodies cannot keep up, resulting in swelling.  As the swelling reaches the limit of the penile skin, the penis becomes firm.  The pressure of the spongy corpora cavernosa against the skin partially closes the veins, helping to maintain the erection.  Erection continues until the signals from the brain stop, but erections are not consistent; waking and waning are normal, even during intercourse.

Changes in Erections

Almost all men experience occasional changes in their erections. Erection changes also occur over a lifetime. Not getting an erection does not equal “sexual dysfunction”.

There are many reasons for not getting an erection such as fatigue, stress, not being in the mood for sexual activity, alcohol and/or drug use, partner issues, insufficient sexual stimulation, and so on. As well, lack of erections from time to time does not mean that sexual activity must stop.

Finally, for many men, the misunderstanding and myths associated with erectile dysfunction are often the very reason why they will not seek the treatment for the same. If you are also experiencing erection problems, it is important to address the issue in the first place and discuss the problem with your doctor. Erection problems often add to the normal pressures of a relationship and may bring increased feelings of despondency, lack of confidence and lowered self-esteem.


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