Andrew Siegel MD 2/20/16
Lost In Evolution
Many mammals have a bone in the penis (os penis) that maintains constant penile stiffness. This is the case with primates including gorillas and chimpanzees, but–for better or for worse– is not the case with human males. The good thing about having an os penis is that there is no such thing as ED in primates, as males are “ever ready.” The bad thing is having a 24/7/365 “boner,” literally and figuratively. Furthermore, having a bone in the penis makes it much more susceptible to injuries such as a fracture of the penis.
The Human Penis
The human penis is a highly evolved and unique organ comprised of 3 cylindrical chambers that contain erectile sinus tissue. These cylinders run the length of the external and internal aspects of the penis. The main “erectile apparatus” consists of the paired cavernous chambers with the ischiocavernosus muscle (IC) that surrounds and supports them. The auxiliary “erectile apparatus” is the head of the penis (glans) with the solitary spongy erectile chamber that envelops the urinary channel and the bulbocavernosus muscle (BC) that surrounds and supports it. The IC and BC muscles are two of the all-important pelvic floor muscles that provide supportive, sphincteric and sexual functions.
The paired cavernous erectile chambers become rigid at the time of sexual stimulation and provide the wherewithal for vaginal penetration. The head of the penis and spongy chamber provide additional plumpness and fullness, but not rigidity.
Blue arrows point to paired cavernous chambers that become rock-hard with stimulation. Red arrow points to solitary spongy chamber and yellow arrow to head of penis, both of which become plump with stimulation. (From Gray’s Anatomy of the Human Body, 20th Edition, original publication 1918, public domain)
IC and BC muscles that surround the inner aspects of the cavernous chambers and spongy chamber respectively. These pelvic muscles support the roots of the penis and when they contract they push pressurized blood into the external penis, creating rock-hard rigidity. (Illustration by Christine Vecchione from “Male Pelvic Fitness: Optimizing Sexual & Urinary Health”)
Did you know that penile erectile sinus tissue is virtually identical to nasal sinus tissue? … IDENTICAL: a pathologist would be hard pressed (no pun intended!) to tell the difference between the two under a microscope. Congested sinuses = penile erection. The oral ED medications increase blood flow to both the nasal and penile sinuses and thus commonly cause sinus congestion as a side effect.
Clever Mother Nature
Nature evolved a brilliant alternative to the os penis for human males. In the absence of such a practical bone, nature capitalized on principles of hydraulics. Blood—not used for its typical purpose (transporting oxygen and other nutrients)—is pressurized to create rock-hard penile rigidity. This process has 3 requirements:
- arterial inflow of blood to the penis
- relaxation of the smooth muscle within the erectile sinus tissue to allow the penis to inflate
- trapping blood to maintain the erection
The blood trapping mechanism is incompletely deciphered, but our current understanding is that as the erectile sinus tissue becomes swollen with blood, the vessels that conduct blood away are pinched closed. The IC and BC muscles also play a key role by tourniquet-like compression of the inner erectile chambers, forcing pressurized blood into the erectile chambers. Penile high blood pressure in excess of 200 mm– the only place in the body where hypertension is desirable and necessary –is what is responsible for penile rock-hard rigidity.
Did you know that Dr. Gray of Gray’s Anatomy 1909 textbook referred to the IC muscle as the “erector” muscle and the BC as the “ejaculator” muscle?
Observe Your IC and BC Muscles In Action
The next time you get an erection, stand up and observe your penis. Vigorously contract your IC and BC muscles (by tightening up the anus) and observe what happens as more hydraulic fuel (blood) surges into the penis: the erect penis should lift up and point to the heavens above…pelvic floor muscle magic!
Erectile Dysfunction
ED can result from a problem in any of the three hydraulic requirements. If you cannot obtain an erection, it is most often due to impaired arterial blood flow to the penis or to a problem with the smooth muscle of the sinus tissue, which fails to relax appropriately and thus will not allow penile inflation. Similar to high blood pressure—which is commonly due to arterial smooth muscle becoming stiffer—failure of relaxation of the smooth muscle within the erectile sinus tissue is often an age-related problem.
If you can achieve an erection but lose it prematurely, it is often due to two causes: One is venous leakage of blood from the sinuses. The other is weakened IC and BC muscles. Unfortunately, there is not a lot that can be done about age-related impaired functioning of the erectile sinus tissue that promotes venous leakage. However, healthy lifestyle measures will optimize function of the erectile sinus tissue and smooth muscle. This includes the following: good eating habits, maintaining a healthy weight, engaging in exercise, obtaining adequate sleep, consuming alcohol in moderation, avoiding tobacco and minimizing stress. The good news is that the IC and BC muscles are capable of being strengthened to improve their form and function, improving the blood trapping mechanism to enhance erectile rigidity and durability. This is possible through Kegel exercises, a.k.a. pelvic floor muscle training programs (see below).
Wishing you the best of health,
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”: www.HealthDoc13.WordPress.com
Author of Male Pelvic Fitness: Optimizing Sexual and Urinary Health: available in e-book (Amazon Kindle, Apple iBooks, Barnes & Noble Nook, Kobo) and paperback: www.MalePelvicFitness.com. In the works is The Kegel Fix: Recharging Female Pelvic, Sexual and Urinary Health.
Co-creator 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: www.PrivateGym.com or Amazon.
Tags: Andrew Siegel MD, Arnold Kegel MD, bulbocavernosus muscle, erectile dysfunction, erection, ischiocavernosus muscle, male pelvic fitness, pelvic floor muscle training, pelvic floor muscles, penis, Private Gym, venous leakage
Our Greatest Wealth Is Health 
May 30, 2016 at 4:46 PM |
Hi
I have erectile difficulties, and I believe the cause is that the smooth muscle can’t fully relax. What are the main reasons for this, and what can be done so the smooth muscle completely relaxes?
Thanks
May 30, 2016 at 5:41 PM |
Failure of smooth muscle relaxation of the arterioles and sinus tissue within the erectile chambers is a common cause of ED, often age-related and paralleling the inability of arterial smooth muscle to relax in the arterial tree of the body, which is a common cause of high blood pressure. A healthy lifestyle is first-line treatment, as it is for hypertension, but that is not always sufficient to manage the problem, which often requires medication in both circumstances.