II. How Erections Work
The simplest way to think of an erection is to think of a simple hydraulic process like the inflation of a bicycle tire. To inflate a bicycle tire, you need a hose to transfer air into the tire, and when the hose is removed, there is a valve that is closed tightly to maintain that air pressure. I have already described the two erection arteries that carry blood into the penis (the hoses), and as the blood fills up the lacunar spaces and they expand, the previously mentioned emissary veins get trapped and compressed (the valve). The valve mechanism is critical to the generation of good rigidity and maintenance of an erection. Indeed, the most common cause of men losing an erection in the middle of intercourse is because this muscle, under adrenaline control, contracts precipitously allowing the veins to carry blood out of the penis rapidly.
So for erection to function, there are a number of key elements that need to be in working order. Firstly, the arteries need to be healthy. Next, the nerves need to be functioning. And finally, the erectile tissue needs to be in good condition. Arterial blockage will reduce the blood flowing into the penis, and this will lead to erection dysfunction. Cavernous nerves that are injured will not supply nitric oxide to allow an erection to occur, and erection tissue which is injured due to diabetes, cigarette smoking, radiation therapy or the chronic absence of erections will also lead to erectile dysfunction.
The nerves are not the only source of nitric oxide, as the endothelium also supplies nitric oxide and is a key regulator of maintenance of erection. In addition to erectile smooth muscle needing to be healthy, so too must the endothelium. It is now known that conditions such as high blood pressure, high cholesterol, diabetes, and cigarette smoking, all cause endothelial dysfunction and this is why these men have a higher incidence of erectile dysfunction than the general population. There are more than 20 neurotransmitters (chemicals that come from the nerves) that are involved in erectile function, but the most important ones are nitric oxide, which is a pro-erection chemical, and adrenaline, which is the world’s most potent anti-erection chemical. Adrenaline, which is known as the “fight or flight” hormone, is released by the adrenal glands during periods of stress, such as being in a fight or running away from something. Increased adrenaline levels are noted in men during high stress, chronic fatigue, and when they are anxious, irritated, annoyed, upset, or worried. This is why stress is a cause of erectile dysfunction.
When a man is aroused, areas within the brain and within the spinal cord increase nerve signals, which causes increased blood flow through the cavernosal arteries. These signals also cause relaxation of the erectile tissue with an increase in the size of the lacunar spaces. As the blood flows into these spaces, the erectile tissue expands in a three-dimensional fashion, compressing the emissary veins, and a rigid erection occurs. Upon removal of the sexual stimulus (generally after orgasm), the nitric oxide level drops precipitously and adrenaline assumes its usual role of keeping the penis flaccid. Then the erectile tissue contracts, blood makes its way back into the general circulation, and erection dissipates.
III. Reproductive Organs
Besides the penis, there are a number of other reproductive organs that should be considered, including the seminal vesicle and the prostate itself. The prostate is a small, walnut-shaped sized organ in the healthy male that sits beneath the bladder and surrounds the urethra. It is separated from the erectile bodies by a muscle layer (the urogenital diaphragm), which is about 1 cm in thickness. The prostate is composed of two major types of tissue: glands, which secrete fluid that is part of semen, and the tissue between the glands known as a stroma. Within the stroma is muscular tissue, and the tone of this tissue in some men dictates urinary function. The prostate produces an acidic fluid, which makes up about 20 to 25% of the seminal fluid (that is, the fluid that is ejaculated). Sitting behind the prostate are two sets of paired structures, the seminal vesicle on the outside and the vas deferens on the inside (Figure 4). The vas deferens travels from the testicle up through the scrotum and the inguinal hernia canal into the pelvis and enters the prostate. This, of course, is the delivery mechanism for sperm. Much to people’s surprise, sperm constitute only 5 to 10% of the volume of the semen that is ejaculated. By the way, normal men produce about 50 million sperm in each cc of semen!
The seminal vesicles are paired structures, which on x-ray look a little like rabbit ears. These structures are glands that produce the vast majority (approximately 70 to 85%) of the seminal fluid. The fluid produced by the seminal vesicle is alkaline in nature and, thus, semen is generally alkaline, as the seminal vesicle fluid amount is larger than the acidic prostate fluid. The seminal vesicles and the vas deferens on each side actually join to form the ejaculatory duct. A right- and left-side ejaculatory duct is present. The ejaculatory duct travels through the prostate and opens into the urethra. The urethra travels through the prostate much in the same way as if you core a whole apple so that there is a channel running through the apple.
Figure 4 • Rear view of the prostate. Sitting behind the prostate are the seminal vesicles (one on each side) and inside these the vas deferens (one on each side). The seminal vesicle and vas deferens join to form the ejaculatory duct, which passes through the prostate.
At the time of radical prostatectomy, not only is the prostate removed, but the seminal vesicles are also removed. Also during the procedure, the vas deferens is cut and ligated (closed off with suture or metal clips) behind the prostate. This is why patients who have had a radical prostatectomy do not ejaculate despite the fact that most of them achieve a normal orgasm. Furthermore, patients who have had a radical prostatectomy are sterile, although they do produce sperm which is made by the testicles and travels into the vas deferens within their scrotum. This sperm can be extracted at a later date, and this can be utilized with a woman’s eggs using in-vitro fertilization (IVF). For patients who want to continue to have children, it is recommended that, prior to radical prostatectomy or prostate radiation, semen be banked for purposes of future attempts of in-vitro fertilization. Saying that, if a man has not banked sperm and decides that he wants to increase the size of his family after radical prostatectomy, a simple procedure can be performed to extract tissue from his testicle which has a very high likelihood of providing enough sperm for the purposes of IVF. Following prostate radiation, the ejaculation ducts and prostate ducts often undergo scarring with time (nothing with radiation occurs immediately), and over the course of one to five years after the completion of radiation, there is a very high likelihood that the man will notice a significant reduction in the amount of fluid ejaculated and may eventually end up with a very similar situation to patients after prostate surgery where there is no ejaculation whatsoever. Again, most patients—post-radiation therapy for prostate cancer—are capable of achieving an orgasm even if they are not ejaculating.
IV. How Ejaculation Works
Much in the same way that the multiple tissues of the penis act in concert to achieve erection, the aforementioned reproductive organs—prostate, seminal vesicles and vas deferens—function together to ensure normal ejaculation. During sexual activity, after a threshold amount of stimulation (this varies dramatically from person to person),ejaculation occurs.The ejaculatory process starts by increased nerve signals coming from the brain to the spinal cord. The ejaculation control center is at the junction of the thoracic and lumbar spinal cord. Nerves travel from the spinal cord and travel to the prostate, seminal vesicle and vas deferens. Interestingly, these nerves use adrenaline (the anti-erection chemical) as their major neurotransmitter for the purposes of ejaculation. The neurotransmitter