The dorsal artery provides for engorgement of the glans during erection, whereas the bulbourethral artery supplies the bulb and the corpus spongiosum. The cavernous artery effects tumescence of the corpus cavernosum and thus is principally responsible for erection. The cavernous artery gives off many helicine arteries, which supply the trabecular erectile tissue and the sinusoids. These helicine arteries are contracted and tortuous in the flaccid state and become dilated and straight during erection. 
Under normal circumstances, when a man is sexually stimulated, his brain sends a message down the spinal cord and into the nerves of the penis. The nerve endings in the penis release chemical messengers, called neurotransmitters, that signal the corpora cavernosa (the two spongy rods of tissue that span the length of the penis) to relax and fill with blood. As they expand, the corpora cavernosa close off other veins that would normally drain blood from the penis. As the penis becomes engorged with blood, it enlarges and stiffens, causing an erection. Problems with blood vessels, nerves, or tissues of the penis can interfere with an erection.
Everyone knows that regular exercise is good for the body and the mind, and in many cases, exercise can be good for relieving stress and helping men’s bodies produce more testosterone. In some cases, however, exercise can be detrimental. This is the case in cycling as long and regular rides can cause the nerves in the perineum to be compacted, leading to a loss of feeling in the penis and/or testicles. Over time, this nerve compaction and damage may lead to either erectile dysfunction or ejaculatory dysfunction.
By contrast, psychogenic impotence typically is abrupt in onset, often in relation to psychological trauma, and may wax and wane. Patients with psychogenic impotence may have total erectile failure with one partner but not another, or be impotent during sexual intercourse but not during self-stimulation. Normally occurring spontaneous erections in the morning suggest psychogenic rather than organic causes for impotence.
Fact is, almost all men experience erection problems from time to time. Sometimes it's a temporary condition that will go away with just power of mind or little treatment. But unfortunately in many cases it may be an ongoing problem. Whatever it is, if you don't want to eventually destroy your self esteem and harm relationship with your lover, immediate treatment is required.
Aging, liver and kidney problems, and concurrent use of certain medications (such as erythromycin [an antibiotic] and protease inhibitors for HIV) slows the metabolism (breakdown) of sildenafil. Slowed breakdown allows sildenafil to accumulate in the body and potentially may increase the risk of side effects. Therefore, in men over 65 years of age, in men with significant kidney and liver disease, and in men who also are taking medications called protease inhibitors, the doctor will initiate sildenafil at a lower dose (25 mg) to avoid accumulation of sildenafil in the body. A protease inhibitor ritonavir (Norvir) is especially potent in increasing the accumulation of sildenafil, thus men who are taking Norvir should not take sildenafil doses higher than 25 mg and at a frequency of no greater than once in 48 hours. Other medications that may affect the level of sildenafil include erythromycin and ketoconazole.
The circulatory system plays a central role in obtaining and sustaining erections. Augmentation of blood flow to the corporal bodies depends on the intravascular pressure in the penile artery. Vascular lesions—typically atherosclerotic, but occasionally fibrotic—and systemic hypotension will limit flow to the corpora. In certain patients, blood flow at rest may be sufficient to obtain an erection but not sufficient to maintain it during intercourse, when the pelvic musculature places greater demands on a compromised blood supply.
Conditions that may be associated with ED include diabetes, [25, 26, 27] hypertension,  , and CAD, as well as neurologic disorders, endocrinopathies, benign prostatic hyperplasia,  , sleep apnea  , COPD,  and depression (see Table 1 below). [32, 33, 34, 35] In fact, almost any disease may affect erectile function by altering the nervous, vascular, or hormonal systems. Various diseases may produce changes in the smooth muscle tissue of the corpora cavernosa or influence the patient’s psychological mood and behavior.
Physical examination should include the assessment of male secondary sex characteristics, femoral and lower extremity pulses, and a focused neurologic examination including perianal sensation, anal sphincter tone, and bulbocavernosus reflex. More extensive neurologic tests, including dorsal nerve conduction latencies, evoked potential measurements, and corpora cavernosal electromyography lack normative (control) data and appear at this time to be of limited clinical value. Examination of the genitalia includes evaluation of testis size and consistency, palpation of the shaft of the penis to determine the presence of Peyronie's plaques, and a digital rectal examination of the prostate with assessment of anal sphincter tone.
That means that as an adult, you need to activate the opposing parasympathetic system through sexually exciting visuals, thoughts and touches to get an erection going. But this nerve transmission is disrupted if you're stressed, anxious or distracted. The latter because you simply don't develop enough total stimulation of your genitals to get an erection, and the former because stress and anxiety all increase adrenaline – a key transmitter in the inhibiting sympathetic nervous system. They quite literally sabotage your erection.
This may be the oldest excuse in the book as a reason not to have safe sex, but research has confirmed that condoms may interfere with some men’s ability to have and hold an erection. For example, a 2006 study found that, over a three-month period, about 37 percent of men lost at least one erection when putting on a condom, or during sex with a condom, SexualHealth.com reported.
Erectile dysfunction is a surprisingly common experience. It has been estimated that at least 1 in 10 men is affected to some extent yet, because of the embarrassment and even shame which has been attached to this condition, many men do not seek treatment. Growing older is a factor, with the number of those experiencing erectile dysfunction increasing with age, but it affects the entire range from the youngest to the oldest.
Not to give your already stressed-out dude one more thing to worry about, but stress is the cause of 20 percent of all erectile problems, from one-off boner blunders to a lingering inability to get and maintain an erection. Of course, sex difficulties are just the tip of the stress-induced health problem iceberg — sustained stress can also lead to insomnia, stomach troubles, chest pains, anxiety, and more severe health issues in the long term.
Most of us are raised to believe that men are ravenous sex-beasts, eternally horny and only pretending to be a part of polite society so that they can find some new crevice to jam their Jeremy Irons into. So the first time we cross paths (and genitals) with a guy who can't get an erection, many of us immediately panic and assume that the problem must be us. We must be profoundly unsexy. After all, what could else possibly stop these hormone-addled maniacs from getting an erection?
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Did you know that erectile dysfunction precedes coronary artery disease in almost 70 percent of cases.2 The arteries in the penis are smaller than those that cause heart disease symptoms, which means they are likely to be affected by blockages sooner. When the arteries in the penis are blocked, keeping an erection will be difficult regardless of your level of arousal.
Well, men go through the exact same anxieties, but the difference between men and women is the result is far more obvious in men. The first thing you need to do when you suspect your man is suffering from anxiety-induced erectile dysfunction is to look at him while you're going down on him and say this: "Is there anything you'd really like me to do? I'm willing to do whatever turns you on."
On the horizon is gene therapy that would deliver genes that produce products or proteins that may not be functioning properly in the penile tissue of men with ED. Replacement of these proteins may result in improvement in erectile function. Experimental animal models have demonstrated improvement in erectile function with gene therapy. Human studies may also demonstrate success with this therapy. Gene therapy may take a long time for regulatory approval and public acceptance.
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.
The recommended starting dose of vardenafil is 10 mg taken orally approximately one hour before sexual activity. A doctor may adjust the dose higher or lower depending on efficacy and side effects. The maximum recommended dose is 20 mg, and the maximum recommended dosing frequency is no more than once per day. Patients can take vardenafil with or without food. As with sildenafil, for vardenafil to be effective, sexual stimulation must occur.
Tadalafil shares the common side effects of the PDE5 inhibitors, however, due to its effect on PDE11, another phosphodiesterase located in muscle, tadalafil has been associated with muscle aches. Back pain and muscle aches occur in less than 7% of men taking tadalafil and in most patients will go away without treatment within 48 hours. When treatment was necessary, acetaminophen (Tylenol) and nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Motrin, Advil) or naproxen (Aleve) were effective. Rarely do the muscle aches and back pain cause men to stop using tadalafil.
Erosion of the prosthesis, whereby it presses through the corporal tissue into the urethra, may occur. Symptoms and signs may include pain, blood in the urine, discharge, abnormal urine stream, and malfunction. If the prosthesis erodes into the urethra, a physician must remove it. If the other cylinder remains intact, it can be left in place. A physician leaves a catheter in place to allow the urethra to heal.
Think of erectile dysfunction as your body’s “check engine light.” The blood vessels in the penis are smaller than other parts of the body, so underlying conditions like blocked arteries, heart disease, or high blood pressure usually show up as ED before something more serious like a heart attack or stroke. ED is your body’s way of saying, “Something is wrong.” And the list of things that cause erectile dysfunction can include: