Male Anatomy
Explanation of male anatomy with regards to semen and sperm production and storage, and how anatomy may affect wet dreams.
Please refer to the following diagram of the male anatomy for reference.
Sperm Production
Sperm are produced in the testes in huge numbers, at a fairly constant rate from puberty until death. Sperm are produced at a rate of approximately 200 million per day, or 8.3 million per hour, or 138,000 per minute, or 2,315 per second! In one week, a fertile man will produce 1.4 billion sperm, in one month, 5.6 billion sperm, and in one year, 6.72 trillion sperm!
Amazing numbers when you think about it.
Sperm are produced within the seminiferous tubules in the testes.
The testes are at a slighly lower temperature the internal body temperature. This is necessary because some of the enzymes needed for spermatogenesis only function normally at the lower temperature. The scrotum helps control the optimal sperm producing temperature by contracting and relaxing the scrotal skin, bringing the testes closer to the body for warmth, and further away from the body for cooling. The hairs and sweat glands on the scrotal skin also help the body regulate the temperature of the testes to perfection for the optimal sperm producing temperature at all times.
Once the sperm are produced, they move to the epididymis, where the sperm grow, mature, and learn to swim. The epididymis is a collection of tubes running along the back side of each testicle, that serve as sperm collectors from each testicle, and as a storage area for the sperm to develop.
It takes 74 days or about 10 weeks for sperm to be produced and fully mature to be ready for ejaculation. So any sperm that you ejaculate today is at least 74 days old! The following diagram illustrates the time line for the spermatogenisis process:
Sperm Storage
Once the sperm are mature and ready for ejaculation, they move to the vas deferens (5), which is a long tube attached to each testicle where the epididymis is, and runs all the way inside the body to where the prostate is located. At the prostate is where the vas deferens connects to the urethra, which runs through the penis and outside the body. Near the prostate end of the vas deferens, the vas deferens fans out considerably and becomes much wider, forming a gland called the ampulla. The ampulla is where the majority of sperm are stored for each ejaculation. When the ampulla is emptied after an ejaculation, more sperm from the rest of the vas deferens moves into the ampulla for the next ejaculation. Think of the ampulla as a bus stop for sperm ready to go travel. The ampulla is inside the body; remember that the testicles need to be several degrees cooler than body temperature for sperm production, but it's not necessary for sperm to be stored at a cooler temperature.
Sperm can be stored inside the male body for approximately 3 weeks after they've matured, after which they die inside the body if not ejaculated. So the entire sperm life cycle inside a man's body if not ejaculated (10 week maturation time + 3 week storage lifespan) is approximately 13 weeks or about 3 months.
The body has the ability to reabsorb dead and excess sperm, and break the sperm protiens back down so they can be carried away by the blood stream. Much is not known about the reabsorption process, however. One area that we do know can definitely reabsorb excess sperm is the in the epididymis. Men who have had vasectomies, have had their vas deferens tubes cut and tied, preventing sperm from traveling from the testes to the rest of the body, and thus preventing any sperm from being ejaculated. However, the testes continue to produce sperm at the rate of hundreds of millions everyday. So what happens to all those sperm if they are blocked and trapped in the testes? The answer is they get reabsorbed by the tiny tubules in the epididymis. However, the epididymis was primarily designed as a nursery area for immature sperm to grow and mature; not as a death chamber for reabsorption, and doctors have noticed changes in the epididymis after a vasectomy. These changes are one of the reasons vasectomy reversals have limited success.
It is unclear what happens to sperm if they happen to die in the ampulla or vas deferens due to prolonged absence of ejaculation. Sperm do not flow back to the epididymis for reabsorption; sperm only move in one direction in the vas deferens. Some theorize that excess and dead sperm are reabsorbed in the ampulla and vas deferens, just as they can be in the epididymis. Others theorize that excess and dead sperm are passed along from the ampulla into the urethra for elimination when urinating.
The other issue which is unclear and may have a direct impact on the frequency of wet dreams without regular ejaculation while awake is at what rate the body can reabsorb excess sperm. If the body produces more sperm than it can reabsorb, there will be a continuous build up of excess sperm, possibly requiring an ejaculation at some point.
Semen Production
Semen is produced by several different glands that operate independently, but come together at ejaculation and orgasm to blend a perfect mixture of fluid to stimulate, feed, and nourish the sperm, to optimize fertility. The majority of an ejaculation by volume is seminal fluid, with sperm only comprising about 5% by volume.
Semen production is almost entirely produced by three glands:
Seminal Vesicles - these grapevine-like glands are about 2 inches long, and reside inside the body, near the prostate gland. The seminal vesicles produce the majority of seminal fluid by volume, at about 60% of total. The seminal vesicles produce a sticky fluid that is clear to yellowish in color, and is very high in fructose, which is essentially sugar. This fructose is designed to help feed the sperm so they will live longer in the vagina. The seminal vesicle fluid also contains various hormones and special proteins to stimulate the sperm to begin swimming (while stored, sperm typically do not swim, and are kind of in a stasis). The seminal vesicles also secrete semenogelin, which is the main protein in the secretion that causes coagulation of the semen, and gives it its sticky, thick consistency.
Prostate Gland - The prostate gland is a small gland about the size and shape of a walnut, about 1.5" across, and 1.2" thick, located inside the body. It surrounds the beginning of the urethra near the bladder. During orgasm, the prostate contracts heavily, and is a major contributor to the pleasurable contraction sensations experienced during orgasm. The prostate gland produces about 40% of the seminal fluid by volume. Prostate fluid is thin and milky white, and gives semen its characteristic milky white appearance. Prostate fluid contains prostate-specific antigens to liquify coagulated semen (basically un-does what the semenogelin produced by the seminal vesicles did). Sperm must go through this coagulation and liquification process to be able to fertilize the egg. Semen typically liquifies in 5-20 minutes after ejaculation.
Cowper's Glands - These are tiny, pea-sized glands near the base of the penis that produce what is commonly known as "pre-cum" or pre-ejaculatory fluid. This fluid is typically produced and expelled in drops before actual ejaculation, but can also be ejaculated with the rest of semen (although in very small amounts relative to the prostate and seminal vesicle secretions). The secretions from the Cowper's glands are completely clear, sticky, yet slick to the touch, and its purpose is to help lubricate and flush out the urethra in preparation for the sperm that will soon be traveling through it. Cowper's gland secretions can occur at any hint of arousal, without even being erect. Some men do not produce pre-cum, while others produce relatively large amounts. Both are normal.
Semen Storage
Production of seminal fluids among these 3 glands is thought to be regulated based on need, however there does appear to be a constant, nominal production of fluid in these glands as well. In other words, the more often ejaculation occurs, the more fluid these glands will produce to attempt to keep the average volume of semen ejaculated at about 2.5ml - 5.0ml, or about 1-2 teaspoons.
Clearly, there are some production capacity constraints with these glands, as for example, if a man ejaculated 3 times in the span of one hour, he will find the first ejaculation contained the most semen, followed by lesser amounts in the second ejaculation, and substantially less in the third ejaculation. However, if he waited until the next day for his fourth ejaculation, he would likely find it has returned to normal volume.
All three glands are thought to be able to reabsorb any excess fluid produced but not ejaculated, however this is only theory. Another theory is that the glands only produce what is needed to fill their storage capacities, and then stop producing until needed again after an ejaculation. A third theory kind of combines these first two, with the thought that these glands reabsorb excess fluid to some extent, but production of new fluid is constant at some nominal level, with the ability to increase production based on need. But the constant nominal production may exceed the reabsorption capacity of the glands, leading to a gradual build-up of seminal fluid, and eventual ejaculation through a nocturnal emission (wet dream) or a spontaneous ejaculation.
This last theory could explain why an ejaculation after one month of abstinence does not contain a half a cup (150ml) of semen that would equate to the average 5ml per day production capacity, but on the other hand such an ejaculation is usually substantially larger in volume than one from a day or even a week of abstinence. This theory would also explain the occurrence of wet dreams after extended periods without ejaculation, and the occurrence of spontaneous ejaculations among those who have gone prolonged periods without ejaculation or wet dreams.
Again, these are just theories though, and all have their weaknesses in practice. The bottom line is doctors and scientists are not sure exactly how the male body regulates production of semen and the reabsorption of excess semen, and how it stores it. One thing is for sure though: semen storage is not as simple as a tank that fills up, and then overflows if there is no ejaculation, leading to a wet dream. There is much more to a wet dream than that simple, but common theory. However, "full glands" may be one of several factors that cause a wet dream.