Learning medicine is hard work!Osmosis makes it easy. It takes your lectures and notes to createa personalized study plan with exclusive videos,practice questions and flashcards, and somuch more. Try it free today!In erectile dysfunction, an individual isunable to develop or maintain an erectionduring sex. This disorder is also called impotence andlike other sexual dysfunction, this conditionbecomes more common with age. Sex can be important within relationships,so erectile dysfunction often carries withit emotional and psychological stigma. In both males and females, sexual activityinvolves a sequence of events called the sexualresponse cycle. This cycle has four phases, excitement, plateau,orgasm, and resolution. During the excitement phase, muscle tension,heart rate, and blood flow to the genitalsincreases. In males, this is called an erection. When these reach the maximum level, it’scalled the plateau phase. Next, the accumulated sexual tension getsreleased during orgasm, causing ejaculationin males. Immediately after orgasm comes the resolutionphase, where the body slowly returns to itsoriginal, un-excited state. Alright, let’s take a closer look at thepenis which is made of three long cylindricalbodies: the corpus spongiosum that surroundsthe penile urethra, and the two corpora cavernosamade of erectile tissue. The corpora cavernosa are wrapped in a fibrouscoat called the tunica albuginea, and eachcorpus cavernosum is made up of blood-filledspaces called the cavernosal spaces. These areas are lined with endothelial cellssurrounded by smooth muscle. Running down the centre of each corpus cavernosumis a large artery called the deep artery whichgives off smaller arteries that supply thecavernosal spaces. Next, blood get drained from these spacesby small emissary veins, which drain intothe deep dorsal vein. This vein then carries the blood back intothe systemic circulation. Now, the penis receives both somatic and autonomicinnervation through the cavernous nerves,which innervate both the corpus spongiosum,and the corpora cavernosa. You can remember the functions of these fiberswith the mnemonic “point and shoot. ”“Point” is erection and it’s causedby “P,” or parasympathetic fibers. “Shoot” is ejaculation and the “S”is for sympathetic. Now, an erection can happen in two ways, eitherby physical stimulation of the penis or genitals,called reflex erection, or by becoming emotionallystimulated by a thought, called psychogenicerection. In both cases, the parasympathetic nerve fibersin the cavernosal spaces release acetylcholinefrom their nerve endings. The acetylcholine bind to muscarinic receptorson endothelial cells, which activates theenzyme nitric oxide synthase. Nitric oxide synthase converts the amino acidarginine into citrulline and nitric oxide. The nitric oxide diffuses into the nearbysmooth muscle cells, and activates guanylatecyclase, which converts GTP molecules to cGMP. This leads to a fall in intracellular calciumlevels causing the smooth muscles to relax,and allowing the cavernosal spaces to expandand fill with blood. The corpora cavernosa grow in size, and compressthe veins, making it harder for blood to leave. With more blood coming in but very littleblood leaving, the penis can maintain an erection. Erectile dysfunction leads to an inabilityto develop and maintain a full erection. Causes include psychological ones like stress,performance anxiety, and depression. In addition, there are a number of physiologiccauses as well. The most common physiologic cause for erectiledysfunction is an inadequate blood supplydue to atherosclerosis and blood vessel damagefrom hypertension. Atherosclerosis is caused by the buildup ofatheromatous plaques that can harden the arteriessupplying the penis, which makes it difficultfor them to dilate. Hypertension causes wear and tear in the endothelialcells, and decrease their ability to producenitric oxide. Another condition that can also damage thearteries is diabetes mellitus. High glucose levels can cause hyaline arteriolosclerosisin the small arterioles in the penis. This is where the arteriole walls develophyaline deposits, which makes it harder forthem to dilate. It also builds up in the capillaries causingthe basement membrane to thicken which makesit harder for oxygen to efficiently move fromthe vascular space to the tissues, causinghypoxia and death of the smooth muscle cells. This hypoxia also causes the parasympatheticnerve fibers to die off. Damaged parasympathetic nerve fibers can’trelease acetylcholine, so there’s less nitricoxide synthase activation, and less nitricoxide is produced. Also, conditions like stroke, multiple sclerosis,and back or pelvic trauma can directly damagethe nerves, leading to erectile dysfunction. Next, endocrine dysfunctions that causes testosteronelevels to fall, like hypogonadism, can causeerectile dysfunction. This happens because low testosterone levelsare associated with lower levels of nitricoxide synthase, which causes less nitric oxideto be produced, and less smooth muscle relaxation. Since testosterone production decreases withage, it’s normal for erections to becomemore difficult to achieve and maintain laterin life. Finally, many medications can cause erectiledysfunction as a side effect. These include diuretics because they leaveless fluid in your circulation, making itdifficult to achieve an erection, and medicationslike antidepressants and methadone, but thosemechanisms are not as well understood. There is no specific test to diagnose erectiledysfunction, so the diagnosis largely relieson the sexual experiences of the individual. Careful questioning of psychological stressorsas well as blood tests to check for testosteroneand glucose levels, a neurological assessment,and duplex ultrasound to evaluate blood flowand atherosclerosis can be done to investigatethe cause of erectile dysfunction. Treatment of erectile dysfunction largelyfocuses on addressing the underlying cause. In terms of medications, PDE-5 inhibitors,like sildenafil can be used. These medications inhibit the PDE-5 enzymein endothelial cells which normally breaksdown cGMP, leading to higher levels of cGMP. That allows for more smooth muscle relaxationwhich facilitates an erection. Sometimes, vacuum erection devices can beused. These devices apply negative pressure aroundthe penis which can help draw in blood toachieve an erection. Finally, surgical procedures like prostheticimplants can be embedded into the penis. They does not cause erections but it couldhelp keep the penis rigid. All right, as a quick recap, erectile dysfunctionis the inability to develop or maintain anerection and it could have psychological ororganic causes. Organic causes can be due to cardiovasculardisorders like hypertension, neurologicalproblems like those caused by diabetes, orhormonal dysfunction where testosterone levelsdecrease. Various medications, like diuretics can alsocause erectile dysfunction as an side effect. There’s no specific test to diagnose erectiledysfunction, so, diagnosis is typically gearedat detecting pre-existing causes. Treatment includes PDE-5 inhibitors like sildenafil,vacuum erection devices, and surgery.