When stimulated by the nerves, the spongy tissue arranges itself in such a way that more blood can be stored in the penis. The veins running through the outer sheath of the penis then compress which stops the blood from leaving the penis. As the blood is stopped from flowing out, the penis fills with blood and stretches within the outer casing, giving an erection.
"Erectile dysfunction can be a very serious issue because it's a marker of underlying cardiovascular disease, and it often occurs before heart conditions become apparent. Therefore, men should consider improving their weight and overall nutrition, exercise more, drink less alcohol and have a better night's sleep, as well as address risk factors such as diabetes, high blood pressure and cholesterol.
Both ED and low testosterone (hypogonadism) increase with age. The incidence of the latter is 40% in men aged 45 years and older.  Testosterone is known to be important in mood, cognition, vitality, bone health, and muscle and fat composition. It also plays a key role in sexual dysfunction (eg, low libido, poor erection quality, ejaculatory or orgasmic dysfunction, reduced spontaneous erections, or reduced sexual activity). 
Commercials for drugs to improve “low T,” or testosterone, the male hormone, are now vying for airtime, but they address desire, not performance. "Male hormone is not an approved treatment for erectile dysfunction," notes Bennett. "It may be used to increase desire in men who have low testosterone, but it doesn’t improve blood flow to an erection." A doctor can do a blood test to check you for low testosterone, but it is a rare cause of ED. Hormone therapy with injections, patches, or gels applied to the skin may improve mood and sex drive, but it likely won’t fix any mechanical issues. Also, testosterone drugs should not be used by men with prostate cancer. Side effects include acne, breast enlargement, prostate enlargement, and fluid retention.
For obvious reasons, ED can be a sensitive subject, one that until relatively recently men were more likely to try to hide than to deal with. Fortunately, a deeper understanding of the variety of causes of erectile dysfunction has led to medications, therapies, and other treatments that can be more individualized and more likely to be effective—and more open discussion about addressing the concern.
There are hundreds of medications that have the side effect of ED and/or decreased libido. Examples of drugs implicated as a cause of ED include hydrochlorothiazides and beta-blocking agents. Medications used to treat depression, particularly the SSRIs such as citalopram (Celexa), escitalopram (Lexapro), fluoxetine (Prozac, Prozac Weekly, Sarafem), fluvoxamine (Luvox, Luvox CR), paroxetine (Paxil, Paxil CR, Pexeva) and sertraline (Zoloft), may also contribute to ED.9 Bupropion (Wellbutrin) which has a predominant effect on blocking the reuptake of dopamine is an antidepressant with lower incidence of ED.10 The side effects of 5ARIs occurring in fewer than 5% of patients can include gynaecomastia, ED, loss of libido and ejaculatory dysfunction.11
Normal erectile function depends on the release of NO and endothelial-dependent vasodilation of the penile arteries. The ‘artery size’ hypothesis, first described by Dr Montorsi, offers an explanation why men are more likely to develop ED before a myocardial infacrtion. It is believed that atherosclerosis affects all vascular beds equally but smaller arteries are more likely to become occluded than larger arteries.31 32 The penile arteries are 1–2 mm while the coronary arteries are 3–4 mm. Thus, the same degree of endothelial dysfunction and atherosclerosis is more likely to occlude blood flow in the penile arteries compared with the coronary arteries. The penile arteries therefore serve as a sensitive indicator for subsequent CVD. This theory is supported by the fact that ED occurs approximately 3 years prior to cardiac symptoms in virtually all patients with chronic coronary syndrome whereas patients with acute coronary syndrome have a much lower prevalence of sexual dysfunction.32
The use of injection therapy requires being taught how to properly inject the medication, determination of the best dose, and monitoring for side effects. It is recommended that one inject on the side of the penis at the base and to alternate sides. Injection therapy should be used no more frequently than once every 24 hours. Individuals on blood thinners must be careful with use of injection therapy.
In a 2005 study, three months of twice-daily sets of kegel exercises combined with biofeedback and advice on lifestyle changes, such as quitting smoking, losing weight, and limiting alcohol, worked far better than just giving the participants advice. “Wearing tight pants will affect impotence along with some other medical conditions like diabetes and heart disease,” which can also affect a man’s degree of impotence, Dr. Jennifer Burns, specializing in family practice with an emphasis on gastrointestinal health at the BienEtre Center, told Medical Daily.
Oral therapies via the PDE5i sildenafil, vardenafil, and tadalafil have been proven to be generally safe and effective in select NED populations. The majority of the treatment effectiveness data has been generated in the SCI population. Data regarding the use of PDE5i outside of the SCI population is lacking (58). Furthermore, the ED that exists in the population with neurologic disorders is often multifactorial and may be caused by psychogenic, psychosocial, hormonal, medication-related and disability-related factors. A careful evaluation of each patient must be performed to isolate these factors prior to initiating vasoactive therapy.
Cosgrove et al reported a higher rate of sexual dysfunction in veterans with posttraumatic stress disorder (PTSD) than in veterans who did not develop this problem.  The domains on the International Index of Erectile Function (IIEF) questionnaire that demonstrated the most change included overall sexual satisfaction and erectile function. [43, 44] Men with PTSD should be evaluated and treated if they have sexual dysfunction.
Lifestyle choices that impair blood circulation can contribute to ED. Smoking, excessive drinking, and drug abuse may damage the blood vessels and reduce blood flow to the penis. Smoking makes men with atherosclerosis particularly vulnerable to ED. Being overweight and getting too little exercise also contribute to ED. Studies indicate that men who exercise regularly have a lower risk of ED.
While millions of men, along with their loved ones, suffer from many similar and frustrating symptoms of erectile dysfunction, we understand no two cases are alike. And that’s why your private consultation with one of NuMale Medical Center’s caring medical providers is completely tailored to you and your partner’s wants and needs. We’ll carefully listen to your unique situation to create an impotence treatment plan that’s best for you, taking into account your full medical history.
It is essential to discuss erectile dysfunction with your doctor, so any serious underlying causes can be excluded and treatment options can be discussed. Many men are embarrassed discussing this issue with their doctor, or even their partner. Open communication with your doctor, and in your relationship, is important for effectively managing this common problem.
A study published in May 2014 in The Journal of Sexual Medicine found that some men can reverse erectile dysfunction with healthy lifestyle changes, such as exercise, weight loss, a varied diet, and good sleep. The Australian researchers also showed that even if erectile dysfunction medication is required, it's likely to be more effective if you implement these healthy lifestyle changes.
Since sexual arousal is a complex process involving hormones, emotions, nerves, muscles, blood vessels and the brain, a malfunction in any of these can lead to ED. Stress, exhaustion and psychological issues can also contribute, and anxiety over maintaining an erection can actually make it harder to attain. In short, any condition that inhibits blood flow to the penis can lead to ED.
The association between low testosterone and ED is not entirely clear. Although these 2 processes certainly overlap in some instances, they are distinct entities. Some 2-21% of men have both hypogonadism and ED; however, it is unclear to what degree treating the former will improve erectile function.  About 35-40% of men with low testosterone see an improvement in their erections with testosterone replacement; however, almost 65% of these men see no improvement. 
There are risks to prosthetic surgery and patients are counselled before the procedure. If there is a post-operative infection, the implant will likely be removed. The devices are reliable, but in the case of mechanical malfunction, the device or a part of the device will need to be replaced surgically. If a penile prosthesis is removed, other non-surgical treatments may no longer work.