Erections occur in response to tactile, olfactory, and visual stimuli. The ability to achieve and maintain a full erection depends not only on the penile portion of the process but also on the status of the peripheral nerves, the integrity of the vascular supply, and biochemical events within the corpora. The autonomic nervous system is involved in erection, orgasm, and tumescence. The parasympathetic nervous system is primarily involved in sustaining and maintaining an erection, which is derived from S2-S4 nerve roots.
Inside the cell, NOS catalyzes the oxidation of L-arginine to NO and L-citrulline. Endogenous blockers of this pathway have been identified. The gaseous NO that is produced acts as a neurotransmitter or paracrine messenger. Its biologic half-life is only 5 seconds. NO may act within the cell or diffuse and interact with nearby target cells. In the corpora cavernosa, NO activates guanylate cyclase, which in turn increases cyclic guanosine monophosphate (cGMP). Relaxation of vascular smooth muscles by cGMP leads to vasodilation and increased blood flow.
The Cancer of the Prostate Strategic Urologic Research Endeavor (CaPSURE) study, designed to determine whether an individual man’s sexual outcomes after most common treatments for early-stage prostate cancer could be accurately predicted on the basis of baseline characteristics and treatment plans, found that 2 years after treatment, 177 (35%) of 511 men who underwent prostatectomy reported the ability to attain functional erections suitable for intercourse. 
Stiffy Solution: Again, saying "stop being so stressed out so you can get boners again" is easier said than done — but a lot of people find sexual dysfunction to be a stronger motivator to live a healthier lifestyle than the threat of, say, a heart attack down the road; so there's a chance that this could actually be a good thing in the long run for your boo, if it helps him take his stress seriously. Relaxation techniques like yoga, exercise, meditation, tai chi, and getting adequate sleep can all lessen the impact of stress on your body (and your dong).
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So not only are erectile problems common, they're nothing for you or your special friend to be freaked out about. Check out the nine most common reasons that dudes sometimes can't get it up, and get ready to become the soothing voice of reason the next time the guy you're with has a hard time pitching his tent in your happy valley. Everything (and every penis) is gonna be fine!
I think that a very powerful argument to young men who want to perform at the highest level is to point out the destructive nature of what they’re doing. If they’re having 18 drinks per week, if they’re having three, four, five drinks at any one time, they’re going to guarantee that their erections are not going to be at the highest level. I can’t tell you the number of men who come in saying, they went out, they had a date, they had a big dinner– which, by the way, is also not a great thing for erections, because all the blood is now going to your gut instead of to the genital area. And how important lifestyle changes are to improving your performance, as well, if not better, than the medications. So make certain that you exercise modestly, not excessively. Make certain that you have a smaller meal on an evening or a day that you want to have a sexual encounter, because you want the blood to go, once again, to the penile area and not to your gut. And really, the whole idea of stress– if you’re stressed out, if you’re worried about a lot of things, if you’re distracted, you can’t initiate that psychic stimulus to your spinal cord and then ultimately to your penis. So stress management is incredibly important.
While erectile dysfunction can occur at any age, the risk of developing erectile dysfunction increases with age. According to the Massachusetts Male Aging Study, the prevalence of erectile dysfunction was 52% in men 40-70 years of age. The prevalence of complete erectile dysfunction increases from 5% at 40 years of age to 15% among men 70 years of age and older.
An alprostadil cream that patients apply into the tip of the penis (the urethral meatus, the opening that urine passes through) is currently available in the UK and Europe. It is currently under review by the U.S. Food and Drug Administration (FDA). After application of the cream, an erection occurs within five to 30 minutes, and the erection lasts one to two hours in men who respond to the cream. Doctors recommend that one use the cream for a maximum frequency of two to three times per week and no more frequent than once every 24 hours. It has essentially the same contraindications and side effects as the other formulations of alprostadil. The cream may cause vaginal burning in roughly 4% of partners. Men should not use alprostadil cream for sexual intercourse with women of childbearing potential unless a condom is used. Researchers have performed controlled trial studies to evaluate the safety and effectiveness of this drug. Overall, 52% of men reported improvement in their erections compared to 20% of men receiving placebo. A later analysis demonstrated that 36% of men using the alprostadil cream had a clinically relevant improvement in vaginal penetration ability and 31% clinically relevant improvement in ability to have successful intercourse to ejaculation.
Another approach is vacuum therapy. The man inserts his penis into a clear plastic cylinder and uses a pump to force air out of the cylinder. This forms a partial vacuum around the penis, which helps to draw blood into the corpora cavernosa. The man then places a special ring over the base of the penis to trap the blood inside it. The only side effect with this type of treatment is occasional bruising if the vacuum is left on too long.
But the main challenge to finding the best ED drug for you may turn out to be health insurance rules—not biochemistry. It's a common practice among insurers to limit the number of pills you can obtain per month. After you hit your limit, the out-of-pocket cost for a single pill can be as high as $20. "The main obstacle in my practice is the cost," Dr. Liou says. You'll need to work with your doctor to get the pill you need at a price you can afford.
#2 Physically exhausted. If you’ve been cranking it at the gym, haven’t been sleeping well, or you’ve been working your ass off at your job, getting tangled up with your lover for even more physically demanding activities may not sound ideal. Physical exhaustion has a direct effect on your ability to get aroused. The only fix for this one is to get some rest.
The risk of impotence increases with age. It is four-fold higher in men in their 60s compared with those in their 40s according to a study published in the Journal of Urology (2000;163:460-463). Men with less education are also more likely to experience impotence, perhaps because they tend to have less healthy lifestyles, eat a less healthy diet, drink more and exercise less. Physical exercise tends to lessen the risk of impotence.
For example, many men with diabetes mellitus may develop erectile dysfunction during their young and middle adult years. Physicians, diabetes educators, and patients and their families are sometimes unaware of this potential complication. Whatever the causal factors, discomfort of patients and health care providers in discussing sexual issues becomes a barrier to pursuing treatment.
How’s this for a win-win: The more sex you have, the less likely you are to suffer from erectile dysfunction, according to a 2008 study published in The American Journal of Medicine. Men aged 55-75 who reported having sex less than once per week had twice the incidence of erectile dysfunction (there were 79 cases of ED per 1,000) as men who have sex once a week (32 cases of ED per 1,000). But if you really want to up your odds, shoot for three times per week (only 16 cases of ED per 1,000). Can you really argue with science, or a perscription to have more sex?
Willful and capricious – erections are funny things. When you're a young man, they seem to pop up at the most inappropriate moments (and the only thing between you and embarrassment is a carefully placed notebook). As you get older, however, they go the other way, and fail to appear on demand no matter how much you try. The sad thing is, my patients often equate this with a loss of masculinity.
Damage to the autonomic pathways innervating the penis may eliminate "psychogenic" erection initiated by the central nervous system. Lesions of the somatic nervous pathways may impair reflexogenic erections and may interrupt tactile sensation needed to maintain psychogenic erections. Spinal cord lesions may produce varying degrees of erectile failure depending on the location and completeness of the lesions. Not only do traumatic lesions affect erectile ability, but disorders leading to peripheral neuropathy may impair neuronal innervation of the penis or of the sensory afferents. The endocrine system itself, particularly the production of androgens, appears to play a role in regulating sexual interest, and may also play a role in erectile function.
Surgery of the penile venous system, generally involving venous ligation, has been reported to be effective in patients who have been demonstrated to have venous leakage. However, the tests necessary to establish this diagnosis have been incompletely validated; therefore, it is difficult to select patients who will have a predictably good outcome. Moreover, decreased effectiveness of this approach has been reported as longer term followups have been obtained. This has tempered enthusiasm for these procedures, which are probably therefore best done in an investigational setting in medical centers by surgeons experienced in these procedures and their evaluation.
Patient can inject medications directly into the corpora cavernosa to help attain and maintain erections. Medications such as papaverine hydrochloride, phentolamine, and prostaglandin E1 (alprostadil) can be used alone or in combinations to attain erections. All of these medications are vasodilators and work by increasing blood flow into the penis. Prostaglandin E1 (Caverject, Edex) is easier to obtain; however, it is associated with penile pain in some individuals. The use of combinations of two or three of these medications can decrease the risk of having penile pain.
The FDA does not recommend alternative therapies to treat sexual dysfunction. Many products are advertised as "herbal viagra" or "natural" sexual enhancement products, but no clinical trials or scientific studies support the effectiveness of these products for the treatment of erectile dysfunction, and synthetic chemical compounds similar to sildenafil have been found as adulterants in many of these products. The United States Food and Drug Administration has warned consumers that any sexual enhancement product that claims to work as well as prescription products is likely to contain such a contaminant.
The observation that TRT enhances the efficacy of PDE5 inhibitors in hypogonadal men taking these therapies with suboptimal response to the PDE5 inhibitors alone has been reported.33 In addition, investigators have demonstrated that TRT in hypogonadal men can improve erectile function even without the benefit of PDE5 inhibitors.33 In addition, guidelines for managing ED in hypogonadal men by the European Association of Urology recommend controlling the man to a eugonadal state prior to initiation of PDE5 inhibitor therapy.36 Testosterone measurement consists of a serum specimen which should be ideally obtained in the morning because of the normal diurnal variation of testosterone which is at its peak in the morning. Since TRT is relatively safe, and men can potentially see an improvement in erectile function, it seems prudent to consider this issue when presented with a patient suffering from ED.
#9 Smokers hell. Bad stimulants such as smoking cigarettes may be having a negative impact on more than just your lungs. That’s right, smoking may lead to a lazy penis. One study shows that 40% of men that suffer from erectile dysfunction are smokers. The good news is that 75% of men reported erectile issues disappear after quitting smoking. What better motivation to quit smoking than having amazing sex? [Read: How to keep an erection up for longer in 20 ways]
The medications are extremely effective, which is very good. And the medications are, for the most part, extremely well-tolerated. But there are, like with any medications, a potential downside. The one absolute downside to the use of any of these erection what we call PDE5 medications is if a patient is using a nitroglycerin medication. And nitroglycerins are used for heart disease and for angina, for the most part, although there are some recreational uses of nitrites. And that’s important because your blood vessels will dilate and your blood pressure will drop. And that is an absolute contraindication.
Men are very susceptible to visual stimulation, particularly as children and teenagers. Seeing anything appealing (say, a person or image) activates pathways in the brain that tell nerves in your lower spinal cord to trigger a release of nitric oxide, which relaxes blood vessel walls and floods your penis with blood, making it hard. Nitric oxide is the key chemical here, as you need a mix released from your nerves AND from your blood vessels to get an erection. If the blood vessels, nerves, or both are damaged, it's difficult to get a hard erection. That's why your doctor may well be interested if you're struggling with erections, as it could be a sign of early heart disease or diabetes.
Then you have to be able to make the right diagnosis. What is the basis for their erectile dysfunction? Is it psychogenic? Is it some sort of neurological or blood vessel or hormonal issue? So you have to make a diagnosis. You have to be able to make an assessment. And then only after those things are done, then you start to think about medications.
Sexual dysfunction and ED become more common as men age. The percentage of complete ED increases from 5% to 15% as age increases from 40 to 70 years. But this does not mean growing older is the end of your sex life. ED can be treated at any age. Also, ED may be more common in Hispanic men and in those with a history of diabetes, obesity, smoking, and hypertension. Research shows that African-American men sought medical care for ED twice the rate of other racial groups.