THE REPRODUCTIVE SYSTEMS • Overall function is to produce offspring • Testes produce sperm and male sex hormones • Ovaries produce eggs and female sex hormones • Mammary glands produce milk
COMPILED BY ASHISH BISHNOI
The reproductive system is a collection of internal and external organs — in both males and
females — that work together for the purpose of procreating.
Due to its vital role in the survival of the species, many scientists feel that the
reproductive system is among the most important systems in the entire body.
Of the body’s major systems, the reproductive system is the one that differs most
between sexes, and the only system that does not function until puberty.
The male reproductive system is responsible for delivering sperm to the female reproductive
MALE REPRODUCTIVE SYSTEM
In males, the reproductive organs include the
penis, the testes, a number of storage and
transport ducts, and some supporting structures.
The two oval-shaped testes (also called
testicles) lie outside the body in a pouch of
skin called the scrotum, where they can
maintain the optimum temperature for
sperm production – approximately 5° F,
lower than body temperature.
Testes are oval-shaped glands responsible for
the manufacture of sperm and the sex hormone
From each testis, sperm pass into a coiled tube
– the epididymis – for the final stages of
INSIDE THE SCROTUM
The scrotum contains two testes
(testicles) where sperm are
manufactured within tubes called
seminiferous tubules, and the
two epididymides where sperm
Unlike female egg maturation,
which occurs in cycles and
ceases at menopause, sperm
production is continuous,
reducing gradually with age.
Each epididymis is a tube
about 20 feet long, which is
tightly coiled and bunched
into a length of just 2 inches.
Each testis is a mass of more than 800 tightly
looped and folded vessels known as
Inside each tubule, sperm begin as blob-like
cells called spermatogonia lining the inner
These pass through a larger stage, as
primary spermatocytes, then become
smaller as secondary spermatocytes, and
begin to develop tails as spermatids.
As all of this happens, they move steadily
towards the middle of the tubule.
The spermatids finally develop into ripe sperm
with long tails.
Thousands of sperm are produced every
second, each taking about two months to
DIFFERENCE IN SEMEN AND SPERM
Semen, also known as seminal fluid, is
much more than just sperm.
Sperm is only about 5 to 10% of any
given male single ejaculation and the rest
is fructose (aka sugar), fatty acids, and
proteins to nourish the sperm during
A man will produce roughly 525
billion sperm during his whole
lifetime and close to 1 billion per
There are around 200 to 500 million
sperm in an average in a single
human ejaculation !!
Sperm cell – A sperm is about 1/500 inch long,
but most of this is a tail.
The sperm head is only 1/5000 inch, about the
same size as a red blood cell.
Sperm develop in the
testes and consist of a
head, a midpiece, and a
The head contains the
nucleus with densely
coiled chromatin fibers
(chromosomes), with a
front section – the
Acrosome that contains
enzymes for penetrating
the female egg.
The midpiece has a central
filamentous core with many
around it, to give it energy
to move the tail which
propels it forward.
The female reproductive system
includes external and internal
The head contains the nucleus with densely coiled chromatin fibers (chromosomes), with a front section – the Acrosome that contains enzymes for penetrating the female egg.
The midpiece has a central
filamentous core with many
around it, to give it energy
to move the tail which
propels it forward.
The female reproductive system
includes external and internal
The vulva and its structures form
the external genitalia.
The internal genitalia include a
three-part system of ducts: the
uterine tubes, the uterus, and
This system of ducts connects to
the ovaries, the primary
The ovaries produce egg cells
and release them for
Fertilized eggs develop inside the
Unlike the male, the female
reproductive organs are located
entirely inside the body.
From Puberty, their function is to ripen
and release an egg at regular intervals,
and, if the egg is fertilized, to protect
and nourish the embryo and fetus.
No eggs are manufactured after
birth – a female is born with a full
The female reproductive glands (ovaries)
are located within the abdomen.
This release occurs roughly once a month
as part of the menstrual cycle.
The ripe egg travels along the fallopian
tube to the uterus, the muscular sac in
which it develops into an embryo and
EGG CELLS FROM THE OVARIES MOVE
THROUGH THE UTERINE TUBES
The uterine tubes (also called Fallopian
tubes or oviducts) connect the ovaries to
The walls of each tube have an external
serous layer, a middle muscular layer, and an
internal mucous layer that is continuous with
the inner lining of the uterus.
Each uterine tube can be divided into three
Isthmus connects with the uterus.
A dilated portion, the ampulla, curves over
Egg fertilization usually occurs in the
ampulla. The eggs then travel through
the isthmus into the uterus.
THE VAGINA: A TUNNEL WITH THREE
The vagina extends down from the cervix, the
lower part of the uterus, to the vestibule, which is
part of the vulva and the external genitalia.
It sits behind the bladder and in front of the
An inner mucous membrane lines the smooth
muscle walls of the vagina.
This lining, like the inner layer of the uterine tubes,
is continuous with the mucous lining of the uterus.
The vagina has three core functions:
It carries menstrual flow outside the body
It receives the male penis during sexual
It serves as a birth canal during labor.
An ovary contains thousands of immature
During each menstrual cycle, follicle-
stimulating hormone (FSH) causes one
egg to begin development; this takes
place inside a primary follicle.
The follicle enlarges as its cells proliferate, and
begins to fill with fluid, becoming a secondary
follicle that moves to the ovary’s surface.
It also increases its production of the hormone
A surge of luteinizing hormone (LH)
causes the follicle to rupture and release
the ripe egg–this is ovulation.
The lining of the empty follicle thickens into a
corpus luteum–a temporary source of
hormones. The ovary contains undeveloped eggs, eggs in follicles at
various stages of maturation, and empty follicles forming
https://www.youtube.com/watch?v=nLmg4 corpora lutea. The bulk of the glandular tissue surrounding
wSHdxQ these follicles is known as the stroma.
EGG AND SPERM HAVE DEVELOPED SOME PRETTY NIFTY TRICKS TO
MAKE CONCEPTION HAPPEN
Fortify the troops – The liquid portion of semen not only provides the sperm with nourishment for the
journey, it actually coagulates in a woman’s vagina after ejaculation, forming a physical barrier that prevents
the sperm from wandering very far in the wrong direction. This protection disappears within half an hour,
when the semen becomes more fluid again.
Call in the transport unit – The cervical canal is a much more welcoming environment, and sperm that
make it there find themselves awash in a sea of cervical mucus. The mucus is specially designed to transport
sperm efficiently when you’re most fertile. As you approach ovulation, your suddenly copious mucus becomes
stretchy, clear and thin and strings of molecules line up like train tracks so that sperm can hop on and ride to
Picking up speed – A just-ejaculated sperm cell has to spend a couple of hours going through biochemical
changes, picking up tail-thrashing speed to help it make its way into the uterus and fallopian tubes to find its
Timing is Important – Sperm must reach their destination within the right time frame for when the egg is
They also need to pick their destination carefully – An egg is usually only present in one of the two
fallopian tubes in any given month. Pick the wrong tube, and the sperm end up hanging out partying together
with no guest of honor in sight.
May the best sperm win!
Note that the egg
has 2 layers that
the sperm needs to
get through – The
surface and then
the Zona Pellucida
which is a
The first sperm
to reach the
oocyte is never
the one to
of sperm cells
must undergo the
helping to degrade
the corona radiata
and zona pellucida
until a path is
created to allow
one sperm to
contact and fuse
with the plasma
membrane of the
FERTILIZATION: A SPERM AND AN EGG
FORM A ZYGOTE
intercourse, some sperm ejaculated from the male penis swim up through the female vagina and uterus toward an oocyte (egg cell) floating in one of the uterine tubes.
The sperm and the egg are called gametes.
They each contain half of the genetic
information necessary for reproduction.
When a sperm cell penetrates and fertilizes an
egg, that genetic information combines.
The 23 chromosomes from the sperm pair with 23
chromosomes in the egg, forming a 46-
chromosome cell called a zygote.
The zygote starts to divide and multiply.
As it travels toward the uterus it divides to become https://www.youtube.com/watch?v=_5OvgQW6FG4
a blastocyst, which will burrow into the uterine wall.
THE ZYGOTE BECOMES AN EMBRYO: DEVELOPMENT
PRIOR TO AND DURING IMPLANTATION
A fertilized egg, or zygote, takes about five days to reach the uterus
from the uterine tube.
As it moves, the zygote divides and develops into a blastocyst, with
an inner mass of cells and a protective outer ring.
The blastocyst attaches to the wall of the uterus and gradually
implants itself into the uterine lining. During implantation, its cells
At day 15 after conception, the cells that will form the embryo
become an embryonic disc. Other cells begin to form support
The yolk sac, on one side of the disc, will become part of the
On the other side, the amnion fills with fluid and will surround the
embryo as it develops.
Other cell groups initiate the placenta and umbilical cord, which will
bring in nutrients and eliminate waste.
The fertilized egg
passes along the
Within 24–36 hours it
has divided into two
cells, then 12 hours
later into four cells,
and so on.
This process is known
At each stage, the
resulting cells become
body cell size.
The zygote divides
several times to form a
cluster of 16–32 cells,
the morula (derived
from the Latin for
At around 3–4 days
after fertilization the
morula leaves the
fallopian tube and
enters the uterine
About six days after
fertilization, the cell
cluster forms a hollow
cavity and is known as a
It floats within the uterus
for around 48 hours
before landing on the
thick uterus lining
softens to aid
of the blastocyst into the
The inner group of cells
will become the embryo
Within the inner cell mass, an embryonic
M 5 minutes
This separates the cell cluster into the https://www.youtube.co
amniotic cavity, which develops into a m/watch?v=UgT5rUQ9E
sac that will fill with fluid and fold around mQ 2.2 minutes
to cover the embryo, and the yolk sac,
which helps to transport nutrients to the
embryo during the second and third
The disc develops three circular
sheets called the primary germ
from which all body structures will
Early in development at the time of gastrulation a small group of cells are “put
aside” to later form oocytes (eggs) and sperm. These cells are described as
primordial germ cells (PGCs) and are a type of stem cell.
Primordial germ cells, the earliest recognizable precursors of gametes, arise outside the
gonads and migrate into the gonads during early embryonic development.
Human primordial germ cells first become readily recognizable at 24 days after
fertilization in a layer of the yolk sac.
Germ cells exit from the yolk sac into the hindgut tissue and then migrate until they
reach the location of the sex organs.
These cells differentiate at different times into male testis before puberty and female
ovary when the girl is young.
As development proceeds, cells continue to
They move to form groups that will become
tissues and organs.
They also specialize to different cell types, as
genes in their chromosomes are switched off or
In general, development is head-down, with the
brain and head taking shape early, then the body,
followed by the arms as small buds, and lastly
By the end of the embryonic stage, eight
weeks after fertilization, all major organs
and body parts are formed.
3 weeks – The neural tube forms. It will become
the spinal cord, enlarged at one end as the brain.
From this time on, the baby is known as a fetus.
The simple tube-like heart pulsates. The embryo is
4/50– 5/50 inch long.
HUMANS MUST DEVELOP MALE OR FEMALE
GONADS AND GENITALIA TO BE CAPABLE OF
Reproductive structures begin to form in the embryonic stage.
By week 6, gonads and genitalia are present but
undifferentiated. Whether they become male or female is
determined by one chromosome delivered by the sperm.
This pair contains an X sex chromosome from the female egg
and either an X or a Y sex chromosome from the male sperm.
If the chromosome pair is XY, the gonads develop into
testes starting in week 7.
If the chromosome pair is XX, the gonads become ovaries
starting in week 8.
Testes secrete testosterone, forming male genitalia
around week 10.
Without testosterone, female genitalia form.
All reproductive structures are in place at birth or shortly after.
At puberty, an increase in sex hormones will grow them to their
The four-chambered heart
beats, sending blood
through simple vessels.
Intestines, liver, pancreas,
lungs, and limb buds can be
The embryo is about 1/5
At this stage, the face and neck take
shape, the back straightens, and fingers
and toes can be differentiated clearly.
The embryo starts to move.
It is now around 1 to 1-1/5 inch in
IN EIGHT WEEKS, THE EMBRYO DEVELOPS; BY
THE END OF WEEK 10, IT BECOMES A FETUS
Fifteen days after conception marks the beginning of the
The embryo contains a flat embryonic disc that now
differentiates into three layers: the endoderm, the
mesoderm, and the ectoderm.
All organs of the human body derive from these
They begin to curve and fold and to form an oblong body.
By week 4, the embryo has a distinct head and tail and a
Over the next six weeks, limbs, eyes, brain regions, and
Primitive versions of all body systems appear. By the end
of week 10, the embryo is a fetus.
This is referring to the gestational age of the fetus.
The little groove or Philtrum that is in between our nose and upper lip is one of the
most important parts of the human face.
The Philtrum or also commonly called as ‘cupid’s bow’ is the hollow space that is in
between our nose and our upper lip.
CHANGES IN THE FETUS
By 12 weeks the fetus has a large head compared
with the rest of its body, but its features are
All major internal organs are developed, and
even tiny nails exist as folds growing on the
fingers and toes.
The external ears, eyelids, and 32 permanent
tooth buds have also formed.
One month later, rapid development allows the
fetus to move its limbs vigorously, although this
is rarely felt by the mother at this stage.
The external genitalia are visible, and a fine
downy hair (lanugo) grows over the body.
As growth continues, the fetus becomes leaner
and wrinkly, but by the seventh to eighth month,
it starts to accumulate fat and assume the
“chubby” appearance of the newborn.
The fetus is now somewhat restricted by the
uterus. The side of the placenta facing the fetus
is smooth and circular in outline, with the
umbilical cord attached at center.
CHANGES IN THE MOTHER
On average, pregnancy lasts for 40 weeks
from the first day of a woman’s last
menstrual period (usually 38 weeks from
By convention, the duration of
pregnancy is divided into thirds, or
trimesters, each lasting for about three
During this time, the mother’s body
undergoes many changes to support the
developing fetus, accommodate its increasing
size, and prepare itself for childbirth and
Breasts become tender and larger, with
darkened areolas; frequency of urination may
increase; nausea and vomiting are common.
The enlarging uterus shows
Heart rate increases
The mother’s forehead and cheek
skin may temporarily darken
(known as the “mask of
From week 10 of pregnancy,
the fetus grows inside the
uterus, fueled by nutrient-rich
blood supplied by the umbilical
The placenta provides oxygen
and nutrients to the fetus and
removes waste products from
the fetus’ blood.
Skin stretches over the abdomen
Slight contractions may be felt
Fatigue, back pain, heartburn,
and occasional breathlessness
MULTIPLE PREGNANCY AND FETAL
The presence of more than one fetus in the
uterus is called a multiple pregnancy.
Twins occur in about one in 80 pregnancies, and
triplets in about one in 8,000.
Both events are becoming more common, partly
due to improved antenatal care and also
increasing use of fertility methods such as IVF
(in vitro fertilization).
After about 30 weeks, the most common fetal
position is head down, facing the mother’s back,
with the neck flexed forward.
Such a position eases passage through the birth
canal. Monozygotic twins – A single fertilized egg, or zygote,
forms an embryo that splits into two. Each develops into a
However, about 1 in 30 full-term deliveries is fetus. The two have the same genes and sex and share
breech, in which the baby’s buttocks emerge one placenta. They look alike and are known as “identical”
before the head. twins.
Most of the time, a woman releases a
single egg during an ovulation cycle.
However, in approximately 1 percent of
ovulation cycles, two eggs are released
and both are fertilized.
Two zygotes form, implant, and develop,
resulting in the birth of dizygotic (or
fraternal) twins. Because dizygotic twins
develop from two eggs fertilized by two
sperm, they are no more identical than
siblings born at different times.
Two eggs are fertilized and develop
separately, each with its own placenta.
They may be different or the same sex.
Also called “fraternal twins”, they have the
same degree of resemblance as any
brothers and sisters.
In frank breech, also called
incomplete breech, the baby
fails to turn head-down in
The hips are flexed and the
legs are straight, extending
alongside the body so that
the feet are positioned
beside the head.
The baby’s legs are flexed at the
hips and knees, so the feet are next
to the buttocks.
This occurs less commonly than
The incidence of breech delivery is
much higher among premature
CHANGES IN THE CERVIX
The cervix is the firm band of muscle and
connective tissue that forms the neck-like
structure at the bottom of the uterus.
In late pregnancy, the cervix softens in
readiness for childbirth.
Sporadic uterine tightenings, known as
Braxton–Hicks contractions, help to thin the
cervix so that it merges with the uterus’s
Braxton–Hicks contractions are usually
painless, and occur through much of
pregnancy, becoming noticeable only after
As labor nears, the cervix tissues lose their
firm consistency. They become softer and
more spongy, affected by natural
substances in the blood called prostaglandins.
The cervix becomes
wider and thinner, and
merges smoothly into
the uterus wall above.
The process of
softening and thinning is
known as effacement.
When pregnancy reaches full-term, the uterus
is the largest and strongest muscle in the
When its muscle fibers shorten, with the
eventual aim of expelling the fetus, it is known
as a uterine contraction or simply a
True contractions, as opposed to Braxton–Hicks
contractions, are regular and become steadily
more frequent, more painful, and longer-
The main area of contraction is in the uterine
fundus (upper uterus), which stretches, causing
the lower uterus and cervix to thin.
Judging when true labor has started can be
difficult due to “false alarms”.
One of the most commonly used
methods of pain relief during labor
and delivery, epidural analgesia, is
delivered via a needle into the space
between the vertebrae and the
spinal column in the lower (lumbar)
region of the back.
It affects the nerve fibers that
detect contraction pains.
A new type of epidural, often
called a “walking epidural”,
reduces pain without removing
sensation, allowing women to
move around during labor and
participate actively in the
BIRTH OF THE BABY
Around week 36 (usually), the process
of labor begins.
In the first stage, dilation, hormones
stimulate downward contractions of the
The contractions push the head of the
fetus against the cervix at the lower
end of the uterus.
The cervix dilates.
In the second stage, expulsion,
powerful contractions push the head
and the rest of the body through the
dilated cervix, and out through the
vagina and the vulva.
The baby is born. Further contractions
expel the placenta to complete the