Heather has taught reproductive biology and has researched neuro, repro and endocrinology. She has a PhD in Zoology/Biology.
From the Testes to the Ductus Deferens
Hi and welcome to the sperm packaging plant. On today's tour we will take you through the process of sperm and semen production and transport. This process begins at puberty in males and continues into adulthood - even into old age.
Stop number 1: the testes. These organs usually come in pairs. This is where sperm production begins. Inside the testes, sperm proceed through the processes of mitosis and meiosis to produce haploid spermatozoa.
These spermatozoa are almost mature but lack flagellar movement and the ability to fertilize an egg. That means they aren't quite mobile yet. They travel from the rete testis, through ducts and into the head of the epididymis.
Stop number 2: the epididymis. This stop marks the start of the male reproductive tract. Sperm entering the epididymis are functionally immature and are immobile.
They enter at the head of the epididymis and they travel down through the body into the tail, where they may be stored until they continue on their path. This process completes the final stages of sperm maturation and takes about two weeks.
Stop number 3: the ductus deferens. The tail of the epididymis curves around and meets up with the ductus deferens. Mature, but still immobile, sperm leave the tail and enter the duct. Here they start their ascent, traveling upwards into the abdominal cavity and around the bladder where the duct curves and starts to descend back down.
Now remember, the sperm at this point are still immobile, so this transport is under the control of peristaltic (or wavelike) contractions of the smooth muscles lining the duct. Near the end, the ductus deferens expands into the ampulla and combines with ducts exiting from the seminal vesicles to form the ejaculatory duct. Sperm will be stored in the ampulla until the male experiences sexual arousal.
Sexual Arousal and Emission
Let's pause a second to talk about where and why sperm have to be stored. The ampulla, ductus deferens and the tail of the epididymis participate in the storage of sperm. You see, sperm aren't needed until the male engages in sexual activity, so they have to have somewhere to wait.
Sexual activity begins with arousal and is followed by a process called emission and then by ejaculation. During emission, sperm is propelled out of the ampulla, into the ejaculatory duct and travels past the accessory glands where it combines with fluids from these glands to produce semen. These glands are stops 4, 5 and 6.
Accessory Glands and the Emission Process
Stop 4 includes our first set of accessory glands: the seminal vesicles. Emission begins at the junction of the ductus deferens and the ejaculatory duct. This is where sperm combines with secretions from the seminal vesicles. These paired accessory glands secrete seminal fluid into the ejaculatory duct that makes up about 60% of the semen.
Not only does seminal fluid contain nutrients for sperm growth, but it is also responsible for beginning the capacitation process. Capacitation is the term used to refer to the process of sperm gaining its motility, or mobility - the ability to move. This begins with seminal fluid and ends when sperm enter the female reproductive tract. So, this means that sperm leaving the ejaculatory duct and entering the prostatic urethra are now mobile and begin beating their flagella.
The ejaculatory duct enters our next accessory gland, stop number 5: the prostate. This is the next stop along the emission path. Here, the ejaculatory duct empties its contents into the urethra after it enters the prostate. As sperm pass through the prostate, more fluid is added to the semen. This fluid is called prostatic fluid and makes up about 20-30% of the semen. From here semen continues on down the urethra where it passes the ducts from our next stop the bulbo-urethral glands.
Stop number 6: the bulbourethral glands. These paired structures release their fluid early on during the arousal process. For this reason it is often called pre-ejaculate and it helps to lubricate the urethra and prepare it for sperm passage.
Final Steps: The Urethra and Ejaculation
Our next stop, stop number 7: the urethra. This is our second to last stop on the pathway. By this time, sperm are as ready as they can be to enter the female's reproductive tract and meet up with the egg. Once past the bulbourethral glands, the semen is forced down the urethra by the constriction of the bulbospongiosus muscle at the base of the penis in the process called ejaculation.
And that's it, all aboard! It's the last and final stop, stop number 8: the moment of no return! Once the ejaculation process starts, the sperm are on their way. May the best man win! They rush down the urethra and are propelled out of the urethral orifice, off with hopes of being the best sperm for the job, the one to fertilize the female's egg and pass on his DNA to the next generation!
And there you have it... from the testes to the female's reproductive tract. The pathway that sperm follow from their testicular site of origin till they exit the male's reproductive tract in search of a female egg to fertilize.
They start out in the testes where, when ready, they are transported to the epididymis for the final stages of maturation. From here they move on to the ductus deferens, where they are stored until needed for sexual activity. Once sexual arousal occurs, the process of emission starts and sperm move through the ejaculatory duct and the urethra, passing three accessory glands along the way.
The seminal vesicles, the prostate gland and the bulbourethral glands all contribute to the production of semen as sperm pass by. Finally, sperm enter the base of the penis and are propelled down the urethra and forced out of the urethral orifice, successfully exiting the male's reproductive tract in the process called ejaculation.
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