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Male Reproductive System: Accessory Gland Functions

  • 0:05 Semen
  • 1:39 Seminal Vesicles
  • 3:45 Prostate
  • 4:29 Bulbourethral Gland
  • 5:21 Lesson Summary
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Lesson Transcript
Instructor: Heather Adewale

Heather has taught reproductive biology and has researched neuro, repro and endocrinology. She has a PhD in Zoology/Biology.

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.

Semen

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:

  1. the seminal vesicles
  2. the prostate gland
  3. the bulbourethral glands

Seminal Vesicles

The seminal vesicles produce about 60-70% of the seminal fluid
Seminal Vesicles Location

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
Prostate Gland Location

Prostate

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.

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