Males require a number of different glands to aid in the production of semen. Find out more about those glands in this lesson covering the male accessory glands.
Okay, class. Today's assignment is simple - all you have to do is count! Count how many sperm are in one tiny little mL of semen. Sounds simple, right? While you do that, let me first go over what exactly semen is.
I know what you're thinking - 'Aren't sperm and semen the same thing?' Well, yes and no. You see, sperm is actually part of the semen and only accounts for about 5% of the total fluid contents of semen. Sperm is produced by the testes and transported up to the male's ductus deferens, where it is stored in a region called the ampulla. It doesn't become part of semen until it is combined with fluids from the male's accessory glands.
So, semen is actually a combination of sperm and fluids secreted from the accessory gland structures found in males. This is what leaves the male's penis during the process known as ejaculation.
Wait, wait. I know your next question - 'What are accessory glands?' Right? Well, accessory glands are specialized structures found in males that produce fluids essential for the motility, nourishment and protection of sperm. These are the topics of today's lesson.
Males have three of these glands, and each one contributes to the production of semen. They are:
- the seminal vesicles
- the prostate gland
- the bulbourethral glands
The seminal vesicles produce about 60-70% of the seminal fluid
The first pair we will talk about are the seminal vesicles. These are paired secretory glands located on either side of the ampulla of the ductus deferens. They secrete about 60-70% of the seminal fluid found in semen. This fluid contains fructose for nutrition because, you know, sperm have to eat, right? It contains fibrinogen to stimulate the formation of a sperm plug or clot in the female after ejaculation. Any guesses as to the reason for this?
Well, it's kind of two-fold. First, it helps keep the sperm inside the female tract, and second is to prevent another male's sperm from fertilizing the female. Now, this may not be that useful in humans, but in the animal kingdom where many males compete over access to the same female, this sperm plug comes in quite handy.
Seminal fluid also contains prostaglandins. Prostaglandins stimulate smooth muscle contractions in both the male and female reproductive tracts. These contractions are known as peristaltic contractions and are wavelike contractions of smooth muscle.
Now, while these contractions can occur in other parts of your body - like in the esophagus as you're swallowing food - within the male reproductive tract, their purpose is to aid in the movement of sperm through the reproductive tract. Why would sperm need help, you ask? Well, they aren't really that mobile when it comes to the navigation of the reproductive tract.
You see, sperm are released from the epididymis, which completes the sperm maturation process, but this maturation process doesn't include giving sperm the mobility, or in other words the ability, to move their flagella.
So, these immobile sperm - they have to wait until they're combined with fluid from the seminal vesicles before they can start practicing their swimming. Now, even though they are somewhat mobile at this point, they can only move forward and aren't really that coordinated yet, so they still need help from the peristaltic contractions to move down the rest of the tract.
Location of the prostate gland
After the seminal vesicles, the next accessory gland to contribute to the semen production is the prostate gland. The prostate produces prostatic fluid. This acidic fluid makes up about 20-30% of the semen. It also contains proteins with antibiotic properties that help prevent infections in the male reproductive tract.
Now, notice here how the urethra passes through the center of the prostate. This is why when males have an inflamed prostate, also called prostatitis, they have difficulty urinating because the prostate constricts the urethra, making it difficult for urine, as well as semen, to pass through.
Once the urethra exits the prostate, it passes by the next and last pair of accessory glands - the bulbourethral glands. These are also called Cowper's glands. These glands are important because they secrete a thick, mucus-based fluid also known as pre-ejaculate during the sexual arousal process - so this is before ejaculation.
The bulbourethral gland creates pre-ejaculate fluid
Now, pre-ejaculate lubricates both the urethra and the tip of the penis, making it easier for sperm to pass through. Importantly, this fluid is alkaline in nature. Why is this important? Well, it's because this allows the fluid to neutralize any urinary acids in the urethra, thus protecting the sperm as they pass through the urethra and out of the penis.
And that's it! Now you know the role of each of the accessory glands in the males. So, does anybody have the answer to today's assignment? No? Nobody? Let me guess - too many to count, right?
That's because in 1 small milliliter (mL) of semen, you actually have millions of tiny little sperm - between 50 and 150 million sperm. Isn't that amazing? Especially now that you know sperm only makes up about 5% of semen. Do you remember what makes up the rest of the semen?
It's made up from secretions from the three accessory glands. The seminal vesicles, the prostate and the bulbourethral glands all contribute to the production of semen.
The seminal vesicles provide nutrients and mobility to previously immobile sperm. The prostatic fluid helps by producing proteins with antibiotic properties to help prevent infections. And last but not least, the bulbourethral glands neutralize any leftover urinary acids from the urethra and provide lubrication for the sperm as they pass through. And remember, these are uniquely male structures - they are not found in females. Females have a whole unique set of reproductive structures all their own.
This lesson will help you to:
- Understand the difference between sperm and semen
- Define accessory glands and list the three glands that males have
- Locate the three different glands and list their functions