Video Transcript
In this video, we will learn how to
describe the main structures of the male reproductive system. We will also explain how each part
of the male reproductive system is well adapted to carry out their functions in
sexual reproduction.
The main function of the male
reproductive system is, you guessed it, reproduction. In fact, it is specifically
responsible for part of the process of sexual reproduction in humans, which involves
two parents combining half of each of their genetic material to produce
offspring. This combining of genetic material
occurs through a process called fertilization.
Fertilization involves a sex cell
from a biological male fusing with a sex cell from a biological female. Sex cells are sometimes called
reproductive cells or gametes. A biological male’s sex cells are
called sperm cells, and a biological female’s sex cells are called egg cells. They each contribute half of the
genetic material of a parent so that the cell produced in fertilization, which is
called a zygote, has a full set of genetic material.
Did you know that a healthy
biological male’s reproductive system can produce 1,500 sperm cells every
second? In fact, just one milliliter of
healthy semen, the fluid that contains sperm, can contain as many as 300 million
sperm cells. The main function of these sperm
cells is to fertilize a biological female’s egg cell in sexual reproduction. Let’s take a closer look at how
sperm cells and semen are produced by taking a tour of the male reproductive
system.
Here, we can see an outline of some
of the main structures in the reproductive system of a typical biological male from
a side view. The sperm cells’ journey begins in
the testes, which are sometimes referred to as a biological male’s sex organs or
gonads. Biological males usually have two
testes, each of which is called a testis. A testis is the shape of a small
chicken egg, around three to five centimeters long and three to four centimeters
wide at their thickest point, though this will vary. It is also normal for the two
testes of an individual to vary in size.
The testes are a special type of
organ called a gland. They are responsible for producing
sperm cells and also for producing sex hormones. We will explore this second
function in more detail later. First, let’s continue to describe
the different male reproductive organs.
The testes are found within a sac
of skin called the scrotum, which usually hangs from the male’s body. The scrotum is helpful, as its
external location keeps the testes at a temperature a few degrees lower than the
rest of the normal body temperature. This cooler temperature is more
suitable for the sperm production process. After they are produced in the
testes, sperm cells are stored in the long, coiled tubes that make up the
epididymis, located just outside each of the testes.
To fertilize a biological female’s
egg cell, sperm needs to journey through the male’s reproductive system and out of
his body. This usually occurs when a male is
sexually aroused during or in anticipation of copulation, which is often referred to
as sexual intercourse or simply sex. If sperm cells enter a female’s
reproductive system, they might be able to fertilize one of her egg cells.
Let’s keep track of the pathway
that sperm cells take as they travel from the testes to exit the male’s body with
green arrows. We’ve already covered the first two
stages that occur before the male is aroused. When a male is sexually aroused,
the sperm cells travel from the epididymis along a series of tubelike structures
called ducts. The first duct they enter is called
the vas deferens or a sperm duct. This makes sense, as it transports
sperm. Human males tend to have two sperm
ducts, one leading from each of the testes. Where the two sperm ducts meet, the
sperm cells move into another duct called the urethra. You might already know that both
biological males and biological females have a urethra, as one of its key roles is
transporting urine from the bladder out of the body.
Although the bladder is located
close to the reproductive organs, it is not a part of the reproductive system. Instead, the bladder is responsible
for storing urine before it is removed from the body via the urethra, in a process
called urination. The urethra starts at the base of
the bladder to allow this to occur. In biological males only, the
urethra has another important job. It transports sperm cells from the
sperm ducts out of the male’s body through a process called ejaculation. Let’s clear some space so we have
room to discuss a few things that need to happen first.
The male reproductive system has
several small organs called accessory glands, which release fluids: the prostate
gland, two seminal vesicles, and two Cowper’s glands. These fluids, which are called
seminal fluids, are really helpful as they provide a liquid that sperm cells can
swim through as they pass through the male’s urethra and possibly into a female’s
vagina. Remember, the mixture of these
seminal fluids and sperm cells is called semen. Seminal fluid contains nutrients to
nourish the sperm cells, helping to keep them alive and functioning. It is also alkaline. This is so it can neutralize the
slightly acidic environment in the male urethra and a female vagina, to help the
sperm cells survive for longer. Let’s add some black arrows onto
our diagram to show where seminal fluids are added to the sperm cells.
The prostate is a muscular gland
located just below the bladder. The fluid the prostate gland
produces is added to sperm cells when they travel into the urethra from the sperm
duct. At a similar time, the two seminal
vesicles, which are located behind the bladder, add another fluid component to the
sperm cells, making up between 50 percent to 80 percent of the total semen
volume.
The Cowper’s glands also add fluid
to the sperm cells. These two small glands sit below
the prostate gland on either side of the urethra. The Cowper’s glands are partly
responsible for releasing preejaculatory mucus, which, as the name implies, may
naturally be released from the urethra when the male is sexually aroused before
ejaculation has occurred. This mucus is helpful in
lubricating and neutralizing the urethra to prepare for the transport of sperm cells
out of the body. Sometimes, preejaculatory fluid
contains some sperm cells. Therefore, if it comes into contact
with a female’s reproductive organs, it might still cause fertilization and, as a
result, pregnancy.
Once liquid semen has been formed,
it is ready to be released from the male’s body. In biological males, the urethra
extends through an organ called the penis. The penis is an important organ in
sexual reproduction, and it is also responsible for urination in males. The penis is found just above the
scrotum. It is made of spongelike tissue and
can grow in size upon sexual arousal due to an increase in blood flow, changing from
soft and flaccid to erect and rigidly upright. This feature helps it to enter the
female reproductive system during sexual intercourse, so it can deposit semen into a
female’s vagina.
The urethra ends in a hole,
sometimes called a urosexual opening, at the tip of the penis. As we mentioned earlier, the
process of sperm cells, which are contained within semen, being released from the
penis through this opening is called ejaculation.
Let’s quickly recap the journey of
the sperm cells by looking at the male reproductive system from a front view this
time instead. Sperm cells are produced in the
testes. They are then stored in the
epididymis just outside the testes. Sperm cells are then transported
into the sperm ducts. Where the two sperm ducts meet,
sperm cells are transported into the urethra. Seminal fluids are added to the
sperm cells by the prostate gland, seminal vesicles, and Cowper’s glands to form
liquid semen. This semen, containing the sperm
cells, can then be ejaculated out of the male’s body from his penis via the
urethra. If semen then enters a female’s
vagina, one of the sperm cells might be able to fertilize an egg cell.
We mentioned earlier that the
testes can produce sex hormones. What does this mean? In humans, hormones are produced by
cells within specific types of glands, like the testes. Hormones are chemical
messengers. This means they travel throughout
the body, usually via the bloodstream, to deliver instructions to specific target
cells or organs. This can cause a particular group
of target cells to respond in a particular way. The testes produce the majority of
sex hormones in the male body. The main sex hormone produced by
the testes is testosterone. Testes are usually only found in
biological males.
Interestingly, small amounts of
testosterone are also usually produced in biological females, even though they don’t
have testes. Similarly, typically female sex
hormones, like estrogen, are also released from the testes but in smaller
quantities.
Let’s take a closer look at what
testosterone does. Testosterone is responsible for the
growth of various parts of the male reproductive system, including the prostate
gland and seminal vesicles. It can also control the development
of male secondary sexual characteristics. These are physical characteristics,
not directly involved in reproduction, that start to develop when a person reaches
puberty. Puberty is a period during
adolescence when an individual reaches sexual maturity and becomes physically
capable of reproduction. However, they are unlikely to be
mentally or emotionally ready yet.
Many secondary sexual
characteristics differ between the two biological sexes: males and females. For example, some typical secondary
sexual characteristics in males include their voice breaking and becoming
considerably deeper and the growth of facial and body hair. It may also include the growth of
more muscle. Let’s apply what we’ve learned
about the male reproductive system to some practice questions.
What is the difference between
sperm and semen? (A) Semen is a collection of male
sex cells, and sperm is the fluid that surrounds them. (B) Sperm are the male sex cells,
and semen is sperm cells that have been mixed with seminal fluid. (C) Sperm are the molecules
released by the testes, and semen is the molecules released by the bladder. Or (D) there is no difference
between the two.
Sperm cells are the sex cells of a
biological male. Their main function is to fertilize
a biological female’s sex cell, the egg cell, to create new life. Sperm cells are produced in a
male’s testes and need to travel through his reproductive system to eventually leave
his body if they are going to be successful in fertilization. As the sperm cells are transported
through the male, as represented by the green arrows on the diagram, several fluids,
called seminal fluids, are added to them.
Seminal fluids are produced by
three key glands in the male reproductive system, which have been shown here in
blue: the prostate, seminal vesicles, and Cowper’s glands. Among their other benefits, seminal
fluids are helpful, as they provide a liquid through which sperm cells can swim. The mixture of sperm cells and
seminal fluid is called semen. If semen enters the reproductive
system of a biological female, the sperm cells it contains might be able to
fertilize an egg cell. This means we have found the main
difference between sperm and semen. The correct answer is (B). Sperm are the male sex cells, and
semen is sperm cells that have been mixed with seminal fluid.
Let’s try another question
together.
What part of the male reproductive
system is responsible for producing the majority of the male sex hormones?
Hormones are chemical messengers
that travel through an organism’s body to have an effect on specific target cells
and organs. In humans, hormones are produced by
cells within specific organs called glands. Hormones are usually released into
the bloodstream, which transports them to their target cells.
This question mentions sex hormones
specifically and asks us which part of the male reproductive system is responsible
for producing them. Well, the glands in a biological
male’s reproductive system that are responsible for producing the majority of sex
hormones are called the testes. The main sex hormone produced by
the testes is testosterone. Testosterone is responsible for the
growth of various parts of the male reproductive system. It also controls the development of
male secondary sexual characteristics. These are physical characteristics,
not directly involved in reproduction, that usually start to develop when a person
reaches puberty. Typical secondary sexual
characteristics in males include their voice becoming deeper and the growth of
facial and body hair.
Now we know the correct answer to
this question. The part of the male reproductive
system responsible for producing the majority of male sex hormones are the
testes.
Let’s recap some of the key points
we have covered in this video about the male reproductive system. The testes of a biological male are
responsible for producing sperm cells and sex hormones. Sperm is first transported from the
testes to the epididymis, where they are stored. Just before ejaculation, many of
the sperm cells are then transferred into the sperm ducts and into the urethra,
which moves sperm to the tip of the penis, where it can be ejaculated from the
body. As sperm travels through the male
reproductive system, fluids are added to them by the prostate, seminal vesicles, and
Cowper’s glands to form liquid semen. The main sex hormone released from
the testes is testosterone, which controls the development of secondary sexual
characteristics in biological males.
