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Finally, a word on
pregnancy, as pregnancy is a huge part of reproduction and certainly the most
long lasting part. So, pregnancy results when a sperm successfully fertilizes
an egg to create a zygote, a zygote is a first cell in a new organism that has genetic
material form both mom and dad. And the genetic material has come from the
sperm and the egg that have fused. The zygote goes through a series of
developments and eventually implants itself with the inner wall of a woman’s
uterus to grow. Gestation is the development of the fetus into a baby. So the
development of all the fetus’s organs system’s, when the baby is ready to come
out of the uterus and into the world. She goes through a process called labor.
After the baby’s born. The last step is to give him or her a name.

            If an egg is
fertilized, the resulting zygote attaches to the lining of the uterus, where it
will develop for the next nine months. A hormone that is produced early in
pregnancy stimulates the corpus luteum to continue producing estrogen and
progesterone, and the thickened lining of the uterus is maintained. If the egg
is not fertilized, the corpus luteum stops producing sex hormones. Without
estrogen and progesterone to maintain the thickened uterine lining, the lining
begins to slough off. In the last stage of the menstrual cycle, called menstruation, the lining of the uterus
and blood from the ruptured blood vessels are discharged through the vagina.
Menstruation lasts about five days at the beginning of the follicular phase.
Menstruation continues in most women until about age 50. By then, most of a
woman’s follicles have either matured and ruptured or degenerated. Without
follicles, the ovaries cannot secrete enough estrogen and progesterone to
continue the menstrual cycle, and menstruation ceases. This stage is called menopause.

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  The luteal phase is the development of the
corpus luteum. After ovulation, there is an egg that has been expelled from the
follicle, therefore, there is a remainder of the follicle, and at this point
luteinizing hormone (LH) is really high. Together LH and FCH are going to
induce the old follicle to turn into a structure called corpus luteum, which
just means yellow body in Latin. The follicle was what released estrogen from
its granulosa cells. Since it’s not a follicle anymore it greatly reduces the
amount of estrogen it makes, and it actually begins to mass-produce
progesterone, it still makes estrogen, it’s just not really its primary
product. Progesterone is. After ovulation there is a chance the egg could get
fertilized by a sperm and once it gets fertilized, it’s going to have to
implant into the lining of the uterus called the endometrium. At this stage of
implantation embryo is called blastocyst. Progesterone is a pro-gestation hormone
which stimulates the uterine lining to prepare for implantation and gestation.
During this phase called the secretory phase. I this secretory phase,
progesterone does a few things, it increases blood flow to the endometrium
called spiral arteries, these spiral arteries allow the embryo to eventually
have good access to nutrients from the mother’s bloodstream. Progesterone also
increases uterine secretions from special glands in the endometrium. These
secretions are important for nourishment of the embryo. Finally, progesterone
actually reduces the contractility of the muscles of the uterus so that the
growing embryo does not get too disturbed and does not get expelled out of the
mother’s body too early by those muscles contracting. The corpus luteum then
produces lots of progesterone, and there is still a reasonable amount of
estrogen kicking around. The corpus luteum hormones are doing other things too.
The progesterone and a little bit of estrogen produced by the corpus luteum,
they are going to suppress the FSH and LH production by the anterior pituitary
by that process of negative feedback. The corpus luteum is also producing
inhibin. The inhibin actively inhibits FSH release from the anterior pituitary,
unfortunately for the corpus luteum it needs FSH and LH to survive, since they
are being suppressed by the corpus luteum own release, the corpus luteum start
to atrophy, it starts to wither and die off, when it dies off, and progesterone
and estrogen begin to drop. Two things happen, the first thing is that the end
of the luteal phase is triggered, but the start of the next follicular phase.
At this point menstruation begins to occur and the endometrial lining that has
built itself up and prepared itself for implantation starts to shed and it will
be lost through the vaginal canal and in what we commonly call the menstrual
cycle. Menstruation is a sign that pregnancy has not occurred, this period can
lasts from two to seven days, and women usually lose around 40ml of blood per
menstrual phase. The second thing that happens is when estrogen and
progesterone levels drop is that they stop exerting their negative feedback
effects on FSH and LH release from the anterior pituitary. The FSH and LH
levels begin to go back up again. This increasing FSH then goes on to stimulate
more follicular development in the ovaries to start the whole cycle all over
again over the course of another 28 days, the corpus luteum dying and withering
away is only true when no pregnancy is occurring. Summary: The cells of the
ruptured follicle grow larger and fill the cavity, forming a new structure called
a corpus luteum. Thus, this stage of
the menstrual cycle is called the luteal
phase. The corpus luteum begins to secrete large amounts of progesterone
and estrogen. Progesterone stimulates growth of blood vessels and storage of
fluids and nutrients in the lining of the uterus. This causes the uterine
lining to become even thicker. In addition, increased levels of estrogen and
progesterone cause the pituitary gland to stop secreting LH and FSH (a negative
feedback mechanism). The luteal phase lasts about 14 days. During this time,
estrogen and progesterone levels in the blood rise, while the FSH and LH levels


The sharp rise in
the level of LH that occurs midway through the menstrual cycle causes the
follicle to rupture and release its egg at that time. The release of an egg
from a ruptured follicle is called ovulation.
Following ovulation, an egg is swept into a fallopian tube, where it travels
towards the uterus awaiting fertilization. The egg has enough stored nutrients
to survive about 48 hours.


The follicular phase occurs before
ovulation. We can break the follicular phase into different steps, with each
step being characterized by a stage of growth, we have the primordial follicle
stage. All of our oocytes, before they start to mature are located in the egg
nests in the cortex of the ovary, the egg nests are a group of immature
oocytes. Each oocyte is surrounded by a layer of follicle cells, together the
oocyte pus follicle cells make up the primordial follicle. Each primordial
follicle hangs out in the egg nest of the ovary until the female reaches
puberty. Once puberty hits, the monthly round of follicle recruitment begins,
each month, a subset of primordial follicles are chosen to begin the pathway of
growth and development, waiting to be released from the ovary and becoming
fertilized, once the oocytes have been chosen from the egg nest and have
developed into primordial follicle, they move onto the primary follicle which
the follicles grow in size. As the follicle cells increase in number, they can
be divided into two types, the ones closer to the oocyte are the granulosa
cells and those close to granulosa cells in between adjacent follicles are
thecal cells, both granulosa and thecal cells work together to produce the
female sex hormone estrogen. The next step is the secondary follicle stage,
follicles grow larger in size as they continue to mature. The inside of the
follicle develops this fluid filled spaces that cause the follicle to enlarge.
Only one secondary follicle is usually chose to move on to the tertiary
follicle stage. The tertiary follicle stage is characterized by the presence of
a large fluid filled space inside the mature follicle. Ovulation is the end of
the follicular phase and the start of luteal phase.





Each month the
female reproductive system prepares for a possible pregnancy by undergoing a
series of changes called the menstrual
cycle, for most women, the menstrual cycle lasts about 28 days. During this
time, an egg matures and enters a fallopian tube, where it is able to fuse with
a sperm. If the egg does not fuse with the sperm, the egg degenerates. The
menstrual cycle has four stages: the follicular phase, ovulation, the luteal
phase, and menstruation. These stages are regulated by hormones secreted by the
endocrine system.

Figure 2-
Female reproductive system consists of several internal and external structures
that enable fertilization and development.

The female
reproductive system contains two almond-shaped ovaries that are located in the bottommost
abdomen. Eggs mature near the surface of the ovaries, which are about 3.5 cm
long and 2 cm in diameter. An ovum is released into the abdominal cavity, where
it is swept by cilia into the opening of a nearby fallopian tube, or uterine tube. This narrow passage way leads to
the uterus. The uterus is an organ
in the lower abdomen of a female, where offspring are conceived and in which
they gestate before birth. If an egg is fertilized, it will develop in the uterus.
The lower entrance to the uterus is called the cervix. A sphincter muscle in the cervix controls the opening to
the uterus. Leading from the cervix to the external part of the body is a
muscular tube called the vagina. The
vagina receives a sperm from the penis; it is also the channel through which a
baby passes during childbirth. The external features of the female reproductive
system are inclusively called the vulva.
The vulva includes the labia, folds
of skin and mucous membranes that cover and protect the opening to the female
reproductive system.

Reproductive System


Welcome to the
Reproductive system, the reproductive system is basically a system in our
bodies that includes our sex organs and certain parts of our brain. You can see
the sex organs in two places on the female. This system within our bodies
allows us to reproduce, it allows us to make babies, and to make babies, what
we are doing is combining genetic material from a biological mother’s egg and a
biological father’s sperm to make our offspring. And we simply do this by
sexual intercourse. Like the testes, the female gonads-ovaries- are endocrine
glands that produce gametes. The female reproductive system produce the female
gametes-eggs- for possible fertilization. It also contains organs that allows
fertilization to take place and that holds and nurtures a developing baby. A
female is born with more than 400,000 eggs in her ovaries, the gamete-producing
organs of the female reproductive system. When a female is born, her eggs are
undeveloped and unfertilized. Usually, a female will release 300-400 mature eggs
in the course of her lifetime, averaging one egg about every 28 days from the
time she attains puberty to about age 50. Thus, less than 1 percent of a
female’s eggs reach maturity. Like the sperm formation, the formation of eggs
involve meiosis. Unlike in sperm production- in which four sperm result from
each cell that begins meiosis- only one egg results from each cell that
undergoes meiosis. All immature eggs begin meiosis, but the process is held up
in prophase I until the female attains puberty, when levels of the sex hormones
become high enough to complete the development of the eggs. Controlled by these
hormones, 10-20 immature eggs continue the process of meiosis every 28 days. However,
typically only one developed egg is released each time. A mature egg, or ovum is
about 75,000 times larger than a sperm and is visible to the unaided eye.
Meiosis II is not completed unless a sperm fuses with the egg. If the ovum is
fertilized, it completes the final meiotic division. Only one cell retains most
of the cytoplasm, which provides nutrients that are needed for egg’s survival
through the early stages of development. Deprived of cytoplasm, the other three
meiotic cells die.

Reproductive System

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