Posts Tagged ‘os penis’

Nature’s Brilliant Design: Erection Hydraulics

December 6, 2014

Andrew Siegel, MD  12/6/14

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Humans are hardwired for two basic functions: survival and reproduction. Nature’s forces have made the reproductive process a pleasurable one, and by so doing have ensured the greatest likelihood of reproduction being successful. What a clever bait and switch scheme in which in the seeming pursuit of a feel-good activity—determined by this evolutionary sleight of hand—we have been hoodwinked into reproducing!

The goal of reproduction is the fusion of DNA from two individuals to perpetuate the species. The penis functions as a “pistol” to inject the DNA into the female’s reproductive tract. A flaccid penis is unable to complete this task, as the process demands penetration.

Many mammals—including the gorilla and chimpanzee—have a bone in the penis (the baculum), which functions to keep the penis hard enough for vaginal penetration and injection of the DNA. (There is also a bone in the clitoris called the os clitoridis.) However, the human penis is boneless (as is the human clitoris). While we can debate whether or not this is a good thing, it certainly helps to keep the penis hidden during the workday!

Creating a “Bone” Where One Doesn’t Exist

So what did nature do to overcome this challenging design problem: how do you create bone-like rigidity in a boneless organ?

The answer lies in hydraulics—using blood as a hydraulic mechanism—not the typical use of blood, which is for the transportation of oxygen, carbon dioxide, hormones, nutrients, and wastes to and from our organs. This use of blood as a hydraulic mechanism for erections—both penile erections in men and clitoral erections in women—is nothing short of brilliant…our bodies having evolved to use blood the way a tire uses air, to inflate deflated organs to allow them to function!

Another example of an animal that uses hydraulic action is the jumping spider, which uses blood forced into the legs to straighten them out to facilitate powerful jumps, avoiding the need for muscular legs that are bulky and clearly not spider-like.

Erection hydraulics requires a special means of regulating flow. To do so, the inflow needs to turn on like a gushing faucet and the outflow needs to shut off like a plugged drain in a sink. This is not the usual state of affairs for blood flow to an organ, which typically requires a relatively small amount of inflow to meet basic metabolic needs and an equal amount of outflow, creating a dynamic state of equilibrium. An erection demands that the arteries of the penis function as high-pressure faucets (inflow increasing many times over baseline) and the penile veins to close off completely.

So how has our body evolved this capacity?

The penis is a marvel of design and engineering, capable of increasing its blood flow by a factor of 40-50 times over baseline! This surge happens within seconds and is accomplished by relaxation of the smooth muscle within the arteries supplying the erection chambers and within the erectile sinuses of the erectile chambers. This is not the case of non-genital organs, in which blood flow can be increased upon demand (for example, to our muscles when exercising), but not anywhere to this extent.

Now for a little deviation off course for some interesting trivia:

  1. The spongy tissue in the erectile chambers is virtually identical to the spongy tissue in our facial sinuses. (My pathologist buddy claims that he can’t tell the difference under a microscope.)
  2. When this spongy tissue in the penis or clitoris becomes congested with blood, an erection occurs; when it happens in ours facial sinuses it is known as sinus congestion or a stuffed nose.
  3. The spongy tissue in the erectile chambers is surrounded by connective tissue known as the tunica albuginea, the second toughest connective tissue in our bodies, the toughest being the dura mater that surrounds our brains and spinal cords.
  4. A side effect of the ED meds like Viagra is nasal congestion…now you understand why.
  5. Prolonged erections (priapism) are often treated with the same medications used to treat a stuffed nose, e.g., phenylephrine.

The Important Role of the Pelvic Muscles

So, under the right circumstances the penis becomes swollen (tumescent) with blood. How has our body evolved the capacity to trap the blood so it does not return to the circulation? How does the penis go from swollen to rock-hard rigid?

First, as the sinuses within the erectile chambers fill with blood, they pinch off the veins, which traps blood in the penis. Second, nature—in its typical brilliant way—has designed a means of increasing the blood pressure in the erectile chambers to sky-high levels by means of a “muscular tourniquet” that not only chokes off the exit of blood, but with each squeeze of this specialized muscle, causes a surge of blood with increased filling of the erectile chambers, the end result being bone-like rigidity.

What are the names of these specialized muscles and what muscle group are they part of?

These are the ischiocavernosus and bulbocavernosus muscles (man’s best friends, but equally helpful to the ladies out there) that are part of the group of muscles known as the pelvic floor muscles, which form the floor of the important group of muscles known as the “core” muscles.

When a man has a rigid erection, contracting these muscles will lift up the erection and point it majestically towards the heavens, thank you pelvic floor muscles. You knew that your core muscles were important, but did you realize that the “boner” that you take for granted is based upon well-functioning core muscles?  Ditto for the firm clitoris in the female.

Maintaining & Strengthening Your Pelvic Muscles

So, take good care of your pelvic floor muscles and they will take care of you! Keep them fit, just as you do your other muscles. With aging and lack of physical activity the pelvic muscles become lax, so by increasing the strength, tone, power, and endurance of the pelvic muscles through exercise, you will optimize your erectile rigidity. Moreover, the pelvic muscles assist in delaying ejaculation. Weak pelvic floor muscles can impair the ability to delay ejaculation and voluntary contraction of the pelvic floor muscles can help control ejaculation. When flexed, the pelvic muscles assist in short-circuiting premature ejaculation. Learn more about how you can strengthen and maintain these critical muscles at

Enough of my prose…time to finish with a poem I have written for the occasion:

The Muscles Of Love

Limber hip rotators,

A powerful cardio-core,

But forget not

The oft-neglected pelvic floor


Wishing you the best of health,

2014-04-23 20:16:29


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