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The
sexual and reproductive organs on the outside of a woman's body are called the
external genitals. There are three openings in the genital area. In front is
the urethra, from where urine comes out; below the urethra is the opening to
the vagina which is called the introitus; and the third is the anus from where
a bowel movement leaves the body.
The outer genital area is called the vulva. The vulva includes the clitoris,
the labia majora and the labia minora. The most sensitive part of the genital
area is the clitoris. This is a pea-shaped organ which is full of nerve endings
and its only purpose is to provide sexual pleasure. The clitoris is protected
by hood of skin, and is the equivalent of the male penis.
The labia majora or outer lips surround the opening to the vagina. They are
made of fatty tissue that cushions and protects the vaginal opening between
these outer lips are labia minora or inner lips these lips are sensitive to
sexual stimuli. As they get stimulated, they take on a deeper colour and begin
to swell.
The vagina is a muscular tunnel that connects the uterus (or womb) to the outside
of the body. The vagina provides an exit for the menstrual fluid, and an entrance
for the male's semen, which is ejaculated during sexual intercourse. Normally
flat, like a collapsed balloon, the vagina is extremely flexible and can stretch
to accommodate a tampon, a penis or even a baby's head (during childbirth)!
The walls of the vagina are muscular, smooth and soft. The vagina is a closed
space, which ends at the cervix.
The uterus or the wombs, is the palace where the fertilized eggs grows and develops
into a baby during pregnancy. The uterus lies deep in the lower abdomen the
pelvis-and is just behind the urinary bladder. The uterus is a hollow organ
shaped like a pear end is about the size of the fist. Inside the muscular walls
of the uterus is a very rich lining, namely the endometrium, and it is in this
lining that the fertilized egg gets implanted. If, however, pregnancy does not
occur, this lining is shed along with blood in the form of the menstrual flow.
The neck of the uterus is called the cervix. It connects the uterus to the vagina
and contains special glands called crypts that produce mucus, which helps to
keep bacteria out of the uterus. The cervical mucus also helps sperm in entering
the uterus when the egg is ripe.
Two tubes, known as fallopian tubes, are attached to the upper part of the uterus
on either side and are about 10 cm long. They are about as thick as a piece
of noodles each tube forms a narrow passageway that opens like a funnel into
the abdominal cavity, near the ovaries funnel into the abdominal cavity, near
the ovaries (described later). The ends of the fallopian tubes are draped over
the two ovaries and they serve as a passage for the egg to travel from the ovary
into the uterus. Each fallopian tube is lined by millions of tiny hairs called
cilia that beat rhythmically to propel the egg forward. Of course, the tube
is not just a pathway- it performs other functions too, including nourishing
the egg and the early embryo in its cavity. Also, the sperm fertilize the egg
in one of the fallopian tubes.
The two almond sized ovaries are perched in the pelvis, one on each side, just
within the fallopian tubes' grasp. Each month, at the time of ovulation, a mature
egg is released by an ovary. This egg is "picked up" by the fimbria (a bordering
fringe at the end of the fallopian tubes) and drawn into the fallopian tube.
How does the egg reach the fallopian tube? When ovulation occurs, the mature
egg is releases from the follicle in the ovary. This process of follicular rupture
looks a bit like a small volcano erupting on the ovarian surface. At this time,
the tubal fiimbria, like tentactes, sweep over the surface of the ovary and
actually "swallow" the egg. The egg has a shell called teh zona pelluzida which
looks somewhat like the ring of saturn.The shell is surrounded by a cluster
of nest cells called the corona cells, which serve to narture the egg. These
cells form the cumulus oophorus, which is a sticky gel that protects the egg
and also helps the beating of the hair-like cilia of the fallopian tube to propel
the egg towards the uterus-like, a conveyor belt. The egg must now wait in the
protective confines of the fallopian tube, for a sperm to swim up and reach
it.
The ovary contains about 2 million eggs during the sixth months of fetal life.
From that point onwards, the number of eggs progressively decreases, till only
about 300,000egg cells are left at the time of the birth- a lifetime's stock.
During the fertile years, fewer than 500 of these eggs will be released into
the fallopian tubes- once in each menstrual cycle. One of the existing eggs
becomes matured for ovulation each month, and this limited supply runs out at
the time of menopause. Unlike the testes in the male, which are continually,
churning out billions of new sperm, the ovary never produces any new eggs.
The menstrual cycle:
the aspect of the reproductive system, of which women are most aware, is the
menstrual period or menstrual flow which they have every month. The time from
the beginning of one period to the beginning of the next one is known as the
menstrual cycle. Usually menstrual cycles last about 28-35 days, though any
time period from 3 to 6 weeks is considered normal. If pregnancy does not occur,
the uterus must get rid of this thick lining so that it can grow a new one in
the next cycle. The old lining passes out of the uterus through the vagina as
the menstrual flow.
The menstrual flow thus consists of:
(1) The shed uterine lining;
(2) Blood (this cones from the blood vessels which are torn when the lining
is shed); and
(3) The degenerated unfertilized egg.
If the menstrual flow is heavy, sometimes clots may be formed in it. Sometimes,
the uterine lining is shed as large fragments and these fragments may sometimes
look like bits of pregnancy tissue to some women, who may think they are miscarrying.
The cycle of ovarian hormone production consists of two phases. In the first
phase, called the follicular phase, estrogen plays dominant role. During this
phase the egg matures inside the ovary in its follicle, which consists of: the
egg; the surrounding cells (which nurture the egg and are called granulosa cell
and theca cell); and the fluid (called follicular fluid) which accumulates in
progressively larger amounts during this phase. The follicle secretes a large
amount of estrogen (produced by the granulosa cells) into the bloodstream, and
this estrogen circulates to the uterus, where it stimulates the endometrium
to thicken.
The second phase of hormone production begins after ovulation, midway through
the cycle, when the follicle changes into a small mass of yellow tissue called
the corpus luteum. Travelling through the bloodstream to the uterus, progesterone
complements the work begun by estrogen by stimulating the endometrium to mature
and making it possible for fertilized egg to get implanted in it. In case pregnancy
does not occur, the rate of production of estrogen and progesterone begins to
fall 10 to 14 days after ovulation as the corpus luteum dies, and the endometrium
is shed from the body during the menstrual period.
The male reproductive system begins in the scrotum, which is the sack behind
the penis. This sack contains two testicles, which manufacture a man's sex cells,
called sperm, and the male sex hormone called testosterone. The testicles feel
solid, nut little spongy, like hard-boiled eggs without the shell. They hang
from cord called the spermatic cord.
The testicles produce sperm best when they are at a temperature, which is a
few degrees below the normal body temperature. This is why nature has designed
a scrotum - so that the testes can hang outside the body to keep them cool.
The testicles start producing sperm when a young man reaches puberty. This is
in response to the male sex hormone, testosterone, which starts being produced
at this time. The tested keep on producing sperm for the rest of the man's life.
The sperm are producing inside several hundred coiled microscopic tubules called
seminiferous tubules present in the testes. These tubules converge and collect
in the form of a delta (the mouth of a river) near the upper part of the testis
called the rete testis, which then empties through a series of very small ducts,
called the efferent ducts, out of the testis towards the epididymis. The tail
of the epididymis them leads to the vas deferens a thin cord like muscular tube,
which is part of the spermatic cord and which ends at the ejaculatory duct in
the prostate. In the prostate the ejaculatory duct is joined by the seminal
vesicle ducts and they all open into the urethra in the penis.
Mature sperm take about 75 days to develop in a process called spermatogenesis.
Sperm production takes places as though the sperm were on an assembly line,
with the more mature sperm being passed along towards the center of the tubule,
from where they swim towards the efferent ducts of the testis towards the epididymis.
This assembly line can be very "temperamental"; things may often go wrong, leading
to low sperm counts.
When the sperm leave the testis, they are not yet able to swim on their own.
They acquire the capacity to do so in their passage through the epididymis,
which acts like a "swimming school" for the sperm. They spend between 2 and
15 days here during which they attain maturity and fertilizing potential. During
ejaculation, the muscles of the epididymis and vas deferens contract to propel
the sperm into the ejaculatory duct. Here the sperm is joined by the secretions
of the seminal vesicles and the prostate gland (which contribute the bulk of
the seminal fluid) to form the semen. The powerful muscles surrounding the base
of the urethra then cause the semen to squirt out of the penis at the time of
orgasm. The remarkable aspect of this system is that semen and ureine never
mix in a healthy male (even though the final passage for both is common). This
is because the bladder sphincter muscle contracts during sexual stimulation,
thus closing the exit from the bladder to the urethra during ejaculation, thereby
preventing urine from leaking forward out of he bladder during sex and also
preventing semen from accidentally going backward in to the bladder.
During ejaculation about one teaspoon of semen spurts out of the penis. Semen
has a milky white colour, with the consistency of egg white. Sperm account for
only about 2% to 3% of semen. Most of the semen consists of seminal fluid, i.e.,
the secretion of the seminal vesicles and the prostate gland, which provide
a vehicle for carrying the sperm into the vagina.
A normal ejaculation contains 200 to 500 million sperm. How can so many sperm
fit into only a teaspoon of semen? Simple- sperm are very tiny. If one average
ejaculation filled an Olympic size swimming pool, each sperm cell would still
be smaller than a goldfish. Sperm are the smallest living cells in the human
body and the egg the largest. Basically, sperm are designed so that they can
deliver there contents-the male genetic material- to the egg. This is why sperm
are designed like projectiles- to male DNA is found in the chromosomes in the
sperm head nucleus, and the tail propels the sperm up towards the egg.
Sperm are very fragile. Consequently, very few are able to survive the hazards
swim through the female reproductive system in order to reach the egg. This
is why a male produces such a large number of sperm. Perhaps the reason for
this is also an "evolutionary hangover"- a legacy from our past. To amplify:
female fish deposit eggs on the seabed and the male fish then sprays his sperm
into the sea water. The wastage of sperm in the water is tremendous, and this
is why male fish need to produce millions of sperm, in order to ensure that
at least some sperm reach the egg.
What happen to the sperm if you do not indulge in sex for many days? Unfortunately
you can not store up sperm. If ejaculation does not occur for many days, the
sperm in the reproductive ducts simply die. This is why a sperm count carried
out after many days of abstinence from sex shows a high number of dead or Immotile
sperm. But there is no need to be discouraged by this. The good news is that
just like you cannot store your sperm, you can not run out of sperm either-
masturbation and sexual intercourse cannot "useup" sperm . The body keeps producing
sperm as long as a man has even one normal testicle.
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