The Many Moods Of The Penis

Andrew Siegel, MD   8/22/15

phases of moon

(Thank you and credit for image above, which is in original form, created by Rafa Castillo;

The penis is a very moody organ–it can be temperamental, volatile, excitable, up and down, unpredictable and hot-headed at times.  Like the moon, it has many phases of existence, with a multitude of different states, ranging from soft as a marshmallow to hard as a rock. Between deflated and rigid, there are an infinite number of intermediate states, dependent on the dynamic balance between the constricting and relaxing mechanisms of the blood flow to the erectile chambers of the penis.  Human sexual response is all about “vasocongestion” a.k.a., blood flow.

When the mechanisms that regulate inflow and outflow are not functioning properly, problems may occur, ranging from absent erections to poor erections to satisfactory erections that do not last, to prolonged erections that do not quit (priapism).

The penis is a marvel of human hydraulic engineering with four recognizable “phases”:

  • Flaccid phase—On a scale of 0-100% inflated, this is 0-10%. The penis is lackluster and droopy, with enough blood flow to maintain tissue oxygenation and nutritional and metabolic demands. Since the penis is an organ of both sexual and urinary function, thankfully the flaccid state still allows its owner to enjoy the advantage of standing to urinate.

ad-70507_1280Did you know? The flaccid penis is incapable of penetration, but is fully capable of being stimulated to ejaculation and orgasm.

  • Tumescent phase—On a scale of 0-100% inflated, this is 10%-75%. The penis is softly swollen and engorged, but not stiff. It is in the process of being inflated, gradually filling and plumping as blood is pumped into and trapped within the erectile chambers. Like a New Year’s Eve party blowout, the toy that when blown unfurls and extends outwards, so does the tumescent penis as it becomes inspired and shows some spirit, lifting somewhat from its dangling position.
  • Penetration capable phaseOn a scale of 0-100% inflated, this is about 75%-80% or so. The penis has become firmer, but not rigid and is competent to penetrate, although it may require some manipulation to do so. It is animated and peppy and starts to elevate a bit more.
  • Rigid phaseOn a scale of 0-100% inflated, this is 90%-100%. The penis is as stiff as if it had a bone within. The rock-hard penis makes penetration effortless. The energetic, eager and confident penis now defies gravity, proudly pointing towards the horizon, if not the heavens, when its owner assumes the standing position.


Factors That Lead to Penile Inflation

  • Sensual erotic excitement: sight of a beautiful woman; scent of perfume; sexy whisper; taste of a kiss; soft touch
  • Genital touch: direct stimulation
  • Brain induced erotic stimulation: thoughts, memories, fantasies
  • Dreaming: unique brainstem mediated mechanism that occur during REM (rapid eye movement) phase sleep
  • Spontaneous: occurs for a combination of factors or unknown factors
  • Reflex: full bladder
  • Warm environment: hot bath or shower
  • Gravity: standing upright as opposed to lying down (similar to veins in your arm popping out when arm is lower than heart).

Factors That Lead to Penile Deflation

  • Absence of sexual stimulation
  • Medical issues that interfere with hormones, arterial inflow, venous outflow, nerve supply to penis, smooth muscle in erectile chambers, pelvic floor muscles
  • Medications that interfere directly with blood flow or act centrally on the brain
  • Adrenaline-fueled constriction of penile blood vessels: stress hormone released by fear, anxiety, fighting, fleeing, performance anxiety, etc.
  • Cold exposure (cold shower, bath, swimming, etc.–remember George from the “shrinkage” Seinfeld episode?)
  • Exercise: creates a “steal” of blood flow to large muscles that demand it and away from “unessential” organs
  • Cycling: blood vessels, nerves and pelvic muscles take a beating from compression “trauma”

Hard Science

Note: The following is a brief summary of the science of erections, which may be TMI for many, but will help you understand penis magic.

A limp penis is the state when the arteries and smooth muscle within the erectile chambers are in a constricted state. Penile swelling occurs when stimulation results in increased arterial inflow and relaxation of erectile smooth muscle, permitting filling and expansion of the erectile chambers. The magic chemical that governs this is nitric oxide, present within penile nerves and penile blood vessels. Nitric oxide is what makes it all happen.

 Did you know? Nitric oxide is manufactured from arginine, which is why some feel that arginine supplements may be good for the erectile process; however, the jury is not out on this.

With stimulation, nitric oxide is activated and gets into the smooth muscle cells of the penile arteries and erectile smooth muscle of the erectile chambers where it activates GMP (guanosine monophosphate), which causes the smooth muscle to relax and blood to pour in. This smooth muscle relaxation results in penile blood pressure becoming equal with systolic blood pressure and an engorged penis, plump but not rigid.

Once engorgement occurs, rigidity will follow after the pelvic floor muscles engage. There is no bone in the human penis as there is in many mammals, so nature has evolved a clever trick to generate rigidity using highly pressurized blood.

 Is nature brilliant? Pressurize a liquid to obtain almost a solid state. It’s like freezing water to turn it into ice!

To achieve maximal penile rigidity, penile blood pressure must exceed systolic pressure (the top number of your blood pressure) by 100 millimeters of mercury. This means a penile blood pressure above 220 must be achieved for the average man!

 Did you know? The penis is the only place in the body where high blood pressure is desirable and necessary for proper function. A hypertensive penis is an erect penis and a happy penis. This explains why blood pressure pills are the most common medications associated with erection difficulties.

How does one achieve a hypertensive penis? This is where the “rigidity” muscles come into play. In response to penile stimulation, the pelvic floor muscles (ischiocavernosus and bulbocavernosus) that surround the deep roots of the penis contract rhythmically, clamping venous outflow and compressing the deep roots of the penis, pushing more blood into the erect penis, resulting in penile high blood pressure and full-fledged rigidity. Without the rigidity muscles, the penis would be plump at best.

Did you know?  Would you like to see your rigidity muscles in action?  Stand upright when you have an erection and contract your pelvic floor muscles and watch the penis lift up towards the sky…penis magic! 

After ejaculation, an enzyme known as PDE5 (phosphodiesterase type 5) inactivates the GMP, ending the party, as rigidity dwindles to tumescence to flaccidity. Viagra, Cialis, Levitra and Stendra are PDE5 inhibitors that prevent the inactivation of GMP.

Wishing you the best of health,

2014-04-23 20:16:29

A new blog is posted every week. To receive the blogs in the in box of your email go to the following link and click on “email subscription”:

Author of Male Pelvic Fitness: Optimizing Sexual and Urinary Health: Available in e-book (Kindle, iBooks, Nook, Kobo) and paperback:  In the works is The Kegel Fix: Recharging Female Pelvic, Sexual and Urinary Health.

Co-founder of Private Gym, a comprehensive, interactive, FDA-registered follow-along male pelvic floor muscle training program.  Built upon the foundational work of Dr. Arnold Kegel, Private Gym empowers men to increase pelvic floor muscle strength, tone, power, and endurance: or available on Amazon

Tags: , , , , , , , , , , , , , ,

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: