Anatomy and physiology of the female reproductive system

Anatomy and physiology of the female reproductive system


The female reproductive system includes all
of internal and external organs that help with reproduction. The internal sex organs are the ovaries, which
are the female gonads, the fallopian tubes, two muscular tubes that connect the ovaries
to the uterus, and the uterus, which is the strong muscular sack that a fetus can develop
in. The neck of the uterus is called the cervix,
and it protrudes into the vagina. At the opening of the vagina are the external
sex organs, and these are usually just called the genitals and they’re in the vulva region. They include the labia, the clitoris, and
the mons pubis. The ovaries are a pair of white-ish organs
about the size of walnuts. They’re held in place, slightly above and
on either side of the uterus and fallopian tubes by ligaments. Specifically, there’s the broad ligament,
the ovarian ligament, and the suspensory ligament. And the suspensory ligament is particularly
important because the ovarian artery, ovarian vein, and ovarian nerve plexus pass through
it to reach the ovary. If you slice the ovary open and look at it
(don’t try this at home) there’s an outer layer called the cortex, which has ovarian
follicles scattered throughout it, and an inner layer called the medulla, which contains
most of the blood vessels and nerves. At birth, the ovarian cortex has around two
million follicles – that’s roughly the population of Paris – and they’re called primordial
follicles. Each primordial follicle has a single immature
sex cell called the primary oocyte at the core, and a layer of follicular cells surrounds
this. The primary oocyte has 46 chromosomes, but
eventually it has to turn into a gamete with only 23 chromosomes. To do this, the primary oocytes have to complete
meiosis 1, and in a person’s lifetime only about 400 successfully do that. This process of oocyte development follows
that of follicular development, which can be broken into three stages. The first stage lasts from infancy to puberty,
and during this stage the primary oocyte remains stuck in the prophase step of meiosis 1. So, in other words, the cell is living, but
not dividing. Meanwhile, the primordial follicle turns into
a primary follicle, meaning that the follicular cells that surrounding the primary oocyte
develop into granulosa cells. The second stage of follicular development
begins for a few lucky primary follicles with the first menstrual cycle in puberty, and
a few more primary follicles go into the second stage with each subsequent menstrual cycle. In the second stage, the primary follicles
develop into secondary and eventually tertiary, or graafian follicles. In a secondary follicle, the primary oocyte
is still in the prophase step of meiosis 1, but now the follicle has additional layers
of granulosa cells, as well as theca cells. Theca cells make androstenedione, a sex hormone
precursor, and granulosa cells use the enzyme aromatase to convert it into estradiol – a
member of the estrogen family. In a graafian follicle, a central cavity called
the antrum forms within the follicle, and the granulosa cells secrete a nourishing fluid
for the primary oocyte directly into that antrum. The second stage takes roughly 70 to 85 days
and results in a few fast-growing graafian follicles. The third stage of follicular development
starts when the graafian follicles are ready and occurs during the follicular phase of
the menstrual cycle. So let’s briefly switch gears and go over
the highlights of the menstrual cycle to put that follicular phase into context. The menstrual cycle starts on the first day
of menstrual bleeding, lasts 28 days on average from then. Assuming a 28-day cycle, the follicular phase
makes up the first two weeks of the menstrual cycle, and the luteal phase, the last two
weeks. These two phases are separated by ovulation,
which is when the follicle ruptures and releases an oocyte that is ready to be fertilized. This usually occurs on day 14 of a 28 day
cycle. The menstrual cycle is ultimately controlled
by the hypothalamus, which is at the base of the brain. Before puberty, the hypothalamus constantly
secretes small amounts of a hormone called gonadotropin-releasing hormone, or GnRH. That GnRH travels to the nearby pituitary,
which secretes two hormones of its own – follicle stimulating hormone, or FSH, and luteinizing
hormone, or LH. Once puberty hits, the hypothalamus starts
to secrete GnRH in pulses, sometimes more and sometimes less, and pituitary FSH and
LH make the ovarian follicles develop. The amount of GnRH can be mapped out like
a wave over time, and the frequency and amplitude of the waves of GnRH determine how much FSH
and LH get produced by the pituitary. LH binds to LH receptors on theca cells and
they make progesterone and androstenedione. FSH binds to FSH receptors on granulosa cells
and they make aromatase and, as a consequence, estrogen. Serum levels of estrogen and progesterone
act as feedback for the command center in the brain, which adjusts its hormone production
according to the phases of the menstrual cycle. During the follicular phase of each menstrual
cycle, the few fast-growing graafian follicles enter the third stage of development. Pituitary FSH makes the follicles grow and
the granulosa cells produce more estrogen. In addition to estrogen, the granulosa cells
also secrete a hormone called activin, which stimulates FSH production, as well as binding
to FSH receptors, and the activity of granulosa cell aromatase as well. So early in the follicular phase, a small
rise in FSH, leads to a large increase in estrogen. However, estrogen acts a negative feedback
signal – that is, it tells the pituitary to secrete less FSH and LH. Less FSH means that there is only enough left
to stimulate one follicle. The follicle that has the most FSH receptors
hoards most of this hormone, and becomes the dominant follicle. It usually takes about a week for a dominant
follicle to get selected, and after that happens, the rest of the follicles regress and die
off. The dominant follicle keeps secreting estrogen
for the rest of the follicular phase. The steady increase in estrogen makes the
pituitary more responsive to the pulsatile action of hypothalamic GnRH. When blood estrogen levels reach 200 picograms/milliliter,
dominant follicle estrogen becomes a positive feedback signal – that is, it makes the
pituitary secrete a whole lot of FSH and LH in response to GnRH. This triggers the primary oocyte within the
dominant follicle to finally complete meiosis 1, and turn into a secondary oocyte, which
has 23 chromosomes. The dominant follicle completes its third
stage of development in a blaze of glory called ovulation. That’s when the nearly 2 centimeter sized
follicle ruptures and releases the tiny secondary oocyte into the fallopian tube. The secondary oocyte stops in metaphase of
meiosis 2, and waits for fertilization as the menstrual cycle transitions into the luteal
phase. The luteal phase makes up the second half
of the menstrual cycle – week 3 and week 4, of the 4-week cycle. Right after ovulation, while the LH levels
are still high, the remains of the follicle turn into the corpus luteum, which is made
up of luteinized granulosa and theca cells. Luteinized granulosa cells secrete inhibin,
which inhibits the pituitary gland from making FSH. Without FSH, estrogen levels fall, and the
amount of LH goes back to the level before ovulation. Luteinized theca cells respond to the low
LH concentrations after ovulation by producing more progesterone. So, overall, this means that progesterone
surpasses estrogen as the dominant hormone during the luteal phase of the menstrual cycle.If
fertilization occurs – meaning if a sperm meets the secondary oocyte – then the corpus
luteum continues making progesterone until the placenta forms. If fertilization doesn’t happen, then the
corpus luteum stops making hormones after around 10 days, becomes fibrotic, and is called
the corpus albicans. After ovulation, the secondary oocyte makes
a very quick journey through the peritoneal space and lands in the fallopian tube. The first part is the fimbriae which are the
finger-like projections that surround the ovary and guide the secondary oocyte into
the fallopian tube. Next is the infundibulum and then the ampullar
region which is where fertilization typically happens between the secondary oocyte and the
sperm – this is the magical spot where they meet. which curves around the ovary, and finally
the isthmus region, which opens into the uterine cavity. On the outside, the fallopian tubes are covered
by peritoneum, and supported by the mesosalpinx, which is part of the broad ligament. On the inside, the fallopian tubes have smooth
muscle with an inner lining that has ciliated cells that slowly sweep the secondary oocyte
or zygote towards the uterus. The uterus is a hollow organ that sits behind
the urinary bladder and in front of the rectum. The top of the uterus above the openings of
the fallopian tubes is called the fundus, and the region below the openings is called
the uterine body. The uterus tapers down into the uterine isthmus
and finally the cervix, which protrudes into the vagina. The cervix has a superior opening up top,
and an inferior opening down below, both of which have mucus plugs to keep the uterus
closed off except during menstruation and right before ovulation to allow sperm to reach
the secondary oocyte. The uterus is anchored to the sacrum by utero-sacral
ligaments, to the anterior body wall by round ligaments, and it’s supported laterally
by cardinal ligaments as well as the mesometrium, which is part of the broad ligament. The wall of the uterus has three layers: the
perimetrium, which is a layer continuous with the lining of the peritoneal cavity, the myometrium,
which is made of smooth muscle that contracts during childbirth to help push the baby out,
and the endometrium, a mucosal layer, that undergoes monthly cyclic changes. During the follicular phase of the menstrual
cycle, the endometrium thickens in case fertilization occurs, during the luteal phase, spiral arteries
emerge to bring more nutrients to support the thick endometrium. If fertilization doesn’t occur, the spiral
arteries collapse, and the superficial layers of the endometrium die. During menstruation or menstrual bleeding,
that dead tissue is removed or sloughed off of the uterus through the vagina. The vagina has a muscular wall and is covered
by an inner mucosa with ridges that run along it. The vagina is the passageway for the baby
during childbirth, and it opens up into the vulva. In childhood, a thin sheet of vaginal mucosa
called the hymen partially covers the vaginal opening, and it can break because of exercise,
the use of tampons, or sexual intercourse. The external sex organs, together referred
to as the vulva, are the labia majora which are called “the two greater lips”, labia
minora, or “the two smaller lips”, the mons pubis, or “the mountain of the pubis”,
and the clitoris, a small erectile organ that develops from the same embryonic tissue as
the male penis. It is hooded by a skin fold called the clitoral
hood. Both the labia majora and the mons pubis become
covered in pubic hair during puberty. The labia majora cover the labia minora, and
between the two labia minora there is a space called the vulvar vestibule that includes,
the opening of the vagina and the the urethral opening. All right, so as a quick recap: the female
reproductive system comprises of internal sex organs, such as the ovaries, the fallopian
tubes, the uterus and the vagina, as well as external sex organs such as the labia,
the mons pubis and the clitoris. The ovaries are the female gonads, and they
produce the ova, as well as the female sex hormones. Both the ovaries and the uterus are subject
to the pulsatile hormonal activity of the hypothalamus and pituitary glands.The uterus
is where pregnancy develops, and the baby comes into the world through the birth canal,
or the vagina, that connects the internal and external sex organs.

54 comments

  1. Hi everyone! We've updated this video to improve the discussion about around fertilization and to correct a spelling mistake.

  2. The Video Of Basal Ganglia, which u have already uploaded on Osmosis.org premium , is Lost SomeWhere?? Can't find it anymore…

  3. You don’t show or describe the clitoris properly. The visible part is small, though it is larger and partially wraps around the vaginal canal.

  4. The Male Narrotor is better to understand. This Female Narrotor is difficult to understand. I have even shared this video to my friends they too could not understand well. Please don't let your subscribers down. We love osmosis a lot.

  5. thankyou,my hormonal physiology and ligaments are crystal finally πŸ™Œ, also love the new presenter.

  6. At first glance studying human anatomy seems to bo extremely complicated. It's true that it is complex and your studies will not change that. As for being overwhelming, that can be eleviated if you take it one step at a time. I discovered an article on Sebs Study Crammer extremely helpful for this.

  7. That was the best explanation for female reproductive system….I can't stop saying thanks to you all and please keep up this beautiful work…

  8. Why dont you make videos for ug students to prepare fr pg…yr videos are very interesting…..plz make video so that we can prepare for pg from your videos

  9. I HAD 12 OVERIES. 2 ENDED UP IN AREA OF MALE SCROTOM THERE OVERIES WAS GOING TO HAVE LAYERD INTO RECONSTRUCTED LABIA MINIROA STUPID AS FUCK IDDIOTTS

Leave a Reply

Your email address will not be published. Required fields are marked *