Histology of the Ovary and Ovarian Follicles [Female Reproductive Histology Part 1 of 2]
Summary
TLDRThis video from the Da Vinci Academy's histology course on YouTube explores the female reproductive system's anatomy and histology. It delves into the ovaries' structure, detailing the development stages of ovarian follicles, from primordial to mature, and the role of the corpus luteum in hormone secretion. The script also explains the process of atresia and the importance of the endocrine system in the reproductive cycle, offering a comprehensive guide for students and professionals in the field.
Takeaways
- 📚 The Da Vinci Academy's histology video course is available on YouTube, covering fundamental principles of histology and cell biology.
- 🔍 The course includes a lecture on the female reproductive system, detailing its anatomy and histological organization.
- 👩⚕️ The female reproductive system comprises the ovaries, uterus, fallopian tubes, cervix, and vagina, playing a role in endocrine regulation and reproduction.
- 🌱 The ovaries are covered by a fibrous capsule called the tunica albuginea, which is less defined than in testes.
- 🌼 The ovarian cortex contains follicles at various stages of growth, including primordial, primary, secondary, and mature follicles.
- 🌿 The primordial follicles are immature and formed during the embryonic period, while primary follicles begin to grow under the influence of FSH.
- 🌀 The multilaminar primary follicles feature multiple layers of granulosa cells and the development of the zona pellucida.
- 💧 Secondary or antral follicles are characterized by fluid-filled spaces within the granulosa cells.
- 🍊 The mature follicles, or Graafian follicles, have a large fluid-filled space called the antrum and are ready for ovulation.
- 🔄 Atresia refers to the degeneration of follicles at any stage, marked by apoptosis of oocytes and granulosa cells.
- 🟡 The corpus luteum is a temporary endocrine structure formed after ovulation, secreting progesterone and estrogen, and can transform into the corpus albicans if fertilization does not occur.
Q & A
Where can I find the complete histology video course mentioned in the script?
-The complete histology video course is available on YouTube, and you can access it through the histology playlist link provided in the description below the video.
What are the main components of the female reproductive system discussed in the script?
-The main components of the female reproductive system discussed are the ovaries, uterus, uterine tubes (fallopian tubes), the dome-shaped fundus, the main body of the uterus, the cervix, and the vagina.
What is the tunica albuginea, and how does it differ in the ovaries compared to the testes?
-The tunica albuginea is a fibrous connective tissue capsule covering certain organs. In the ovaries, it is not as well-defined, thick, or dense as it is in the testes.
What is the germinal epithelium, and why is it a misnomer in the case of the ovaries?
-The germinal epithelium is a single layer of simple cuboidal cells surrounding the ovarian surface. It is a misnomer because, when first discovered, it was thought to be the germ cells themselves that gave rise to the oocytes, but this is not the case.
What is the role of the primordial follicles in the ovaries?
-Primordial follicles are immature follicles present in the ovarian cortex and are the majority type of follicles seen before puberty. They contain primary oocytes that are arrested at prophase one of meiotic cell division.
How does the ovary respond to the release of gonadotropin-releasing hormones during puberty?
-During puberty, the release of gonadotropin-releasing hormones (GnRH) leads to the secretion of follicle-stimulating hormone (FSH) from the anterior pituitary, which stimulates the growth of several follicles in the ovary.
What are the different types of ovarian follicles mentioned in the script, and how do they differ?
-The different types of ovarian follicles mentioned are the uni-laminar primary follicle, multi-laminar primary follicle, antral or secondary follicle, mature or graafian follicle, and atretic follicle. They differ in their stages of growth, the number of layers of granulosa cells, and the presence of fluid-filled spaces.
What is the significance of the zona pellucida in the development of follicles?
-The zona pellucida is an acellular barrier that forms on the external surface of the oocyte. It plays an important role in blocking spermatocytes from directly entering the oocyte.
What happens to the mature follicle just before ovulation?
-Just before ovulation, the primary oocyte in the mature follicle is triggered to finish meiosis I and enter meiosis II, becoming a secondary oocyte, which is arrested at metaphase.
What is atresia, and how does it relate to the follicles in the ovaries?
-Atresia refers to the absence, incomplete formation, or degeneration of structures. In the ovaries, numerous follicles at any stage of growth can undergo atresia, which is characterized by signs of apoptosis in both the primary oocytes and granulosa cells.
What is the function of the corpus luteum, and what happens to it in the absence of fertilization?
-The corpus luteum is formed from the remaining granulosa and theca cells after ovulation and secretes progesterone and estrogen, which are crucial for preparing the uterine endometrium for a potential fertilized egg. In the absence of fertilization, the corpus luteum degenerates after about 10 to 14 days, leading to menstruation.
Outlines
🌟 Introduction to Female Reproductive System Histology
This introductory paragraph sets the stage for the histology video course, highlighting its availability on YouTube and the comprehensive coverage of histology and cell biology principles. The focus is on the female reproductive system, starting with the general anatomy and moving into the histological organization of the ovaries and follicles. Key structures such as the ovaries, uterus, fallopian tubes, and vagina are introduced, along with their roles in the reproductive cycle and endocrine regulation. The paragraph also delves into the macroscopic view of the ovaries, discussing the tunica albuginea and the cortical layer containing various follicles and corpus luteum, emphasizing their importance in reproduction and hormonal functions.
📚 Detailed Examination of Ovarian Follicles and Their Development
This paragraph provides an in-depth look at the types of ovarian follicles, their development stages, and the hormonal processes involved. It begins with the primordial follicles and the onset of puberty, leading to the stimulation of follicle growth by gonadotropin-releasing hormones. The description progresses through the various stages of follicular development, including uni-laminar primary, multi-laminar primary, antral (secondary), mature (graafian), and atretic follicles. Each stage is characterized by specific morphological features and the role of the granulosa cells in supporting oocyte development. The paragraph also explains the process of follicle maturation, including the formation of the zona pellucida and the theca layers, which are crucial for hormone production and follicle function.
🔍 The Maturation and Ovulation of the Oocyte
This section delves into the final stages of follicle development, leading up to ovulation. It describes the mature follicle, characterized by the presence of a fluid-filled antrum, and the changes that occur just before ovulation, including the completion of meiosis I. The paragraph explains the arrest of the secondary oocyte at metaphase of meiosis II, which will only be completed upon fertilization. It also discusses the movement of the mature follicle towards the ovarian surface in preparation for ovulation and the protective role of the corona radiata and cumulus oophorus. The importance of these structures in the process of oocyte release and potential fertilization is emphasized.
💡 Atresia and the Role of the Corpus Luteum
This paragraph addresses the phenomenon of atresia, where follicles undergo degeneration at various stages of development. It highlights the constant presence of atresia from the fetal stage to menopause and describes the histological signs of apoptosis in degenerating follicles. The discussion then shifts to the corpus luteum, a temporary endocrine structure that forms from the remnants of the ovulated follicle. The role of the corpus luteum in producing progesterone and estrogen is detailed, along with its importance in preparing the uterus for potential fertilization. The paragraph also explains the life cycle of the corpus luteum, from its formation after ovulation to its degeneration in the absence of fertilization, leading to menstruation.
🌱 The Impact of Pregnancy on the Corpus Luteum and Ovarian Aging
The final paragraph discusses the impact of successful fertilization and pregnancy on the corpus luteum. It explains how the placenta's secretion of human chorionic gonadotropin (hCG) sustains and stimulates the growth of the corpus luteum, prolonging its production of progesterone and estrogen. The paragraph also describes the eventual regression of the corpus luteum after the first trimester of pregnancy as the placenta takes over hormone production. It concludes with an overview of the aging process in the ovaries, where the accumulation of corpora albicans, resulting from the degeneration of corpora lutea, contributes to the visible aging changes in the ovaries over time.
Mindmap
Keywords
💡Histology
💡Female Reproductive System
💡Ovaries
💡Follicles
💡Corpus Luteum
💡Atresia
💡Zona Pellucida
💡Granulosa Cells
💡Theca Cells
💡Germinal Epithelium
💡Primordial Follicles
Highlights
The entire histology video course is available on YouTube, covering fundamental principles of histology and relevant cell biology.
Access to the histology playlist and practice questions is provided through links in the video description.
The female reproductive system lecture discusses the general anatomy and histological organization of the ovaries and various follicles.
The ovaries are suspended within the pelvic cavity by the suspensory and ovarian ligaments.
The uterus is a large pear-shaped structure with two fallopian tubes, a fundus, body, cervix, and vagina.
The ovaries are covered by a fibrous connective tissue capsule called the tunica albuginea.
The ovarian parenchyma is divided into the outer cortical layer containing follicles and the inner medulla.
The cortex contains follicles in various stages of growth, including diverse histology of follicles and corpus luteum.
The germinal epithelium, a misnomer, is a single layer of simple cuboidal cells surrounding the ovarian surface.
The tunica albuginea is an ill-defined layer of dense irregular connective tissue.
Primordial follicles are immature follicles present before puberty, contained within the ovarian cortex.
Follicle stimulating hormone (FSH) stimulates the growth of several follicles each month during the reproductive years.
Different types of ovarian follicles are identifiable based on characteristic morphologies, such as primary, secondary, and mature follicles.
The mature follicle, or Graafian follicle, is characterized by a single enlarged fluid-filled space called the antrum.
Atresia refers to the degeneration of follicles at any stage of growth, observable through signs of apoptosis.
The corpus luteum is a yellow body formed from the remnants of the mature follicle post-ovulation, secreting progesterone and estrogen.
The lifespan of the corpus luteum is approximately 10 to 14 days, degrading in the absence of fertilization and placenta formation.
In the case of successful fertilization, the corpus luteum persists and proliferates due to human chorionic gonadotropin (hCG).
After about five months of pregnancy, the placenta takes over progesterone and estrogen production, allowing the corpus luteum to regress.
Corpus albicans is the dense irregular connective tissue scar that remains after the corpus luteum degenerates.
Transcripts
welcome to the da vinci academy
histology video course
the entire video course is available on
youtube and covers all of the
fundamental principles of histology and
relevant cell biology you can find all
the videos from the course by clicking
the histology playlist link in the
description below
and then you can access the
corresponding practice questions and
histology lab videos by going to our
website which is also linked in the
description below this first female
reproductive system lecture will discuss
the general anatomy of the female
reproductive system and dive into the
histological organization of the ovaries
and variety of follicles
female reproductive system consists of
the two ovaries which are suspended
within the pelvic cavity by the
suspensory ligament which goes up
laterally and superiorly in this fashion
and the ovarian ligament which attaches
the medial aspect of the ovaries to the
lateral aspect of the uterine body
another component of the female
reproductive system would be the uterus
which is this large pear-shaped
structure which has these two uterine
tubes also known as the fallopian tubes
the dome-shaped fundus the main body and
the narrowed inferior portion called the
cervix and it also includes the vagina
which is this fibromuscular tube leading
out into the external opening and while
these organs lay quote-unquote dormant
during childhood from monarchy to
menopause these structures play a
critical role in endocrine regulation of
reproductive cycle as well as the
reproduction itself looking at the
ovaries at macroscopic scale each ovary
is covered on the outside by a fibrous
connective tissue capsule called the
tunica elbogenia it's not quite as well
defined or clear in the ovaries because
it is not as thick or dense as it is in
the testes so dr cooper will discuss
tunica albuginea covering the testes
this structure is comprised of the dense
irregular connective tissue and it forms
a bit of a capsule-like structure for
the ovaries as well as in the testes
the parenchyma of the ovaries are
subdivided into the outer cortical layer
and the inner medulla the cortical layer
contains numerous follicles which are
the oocytes that are surrounded by the
protective ovarian stromal cells and
during the reproductively active age
this cortex will contain the follicles
that are in various stages of growth as
you can see here there's diverse
histology of these follicles of various
sizes in addition to various sizes and
shapes of follicles we may also see some
corpus luteum which is the leftover
follicular cells after the follicle has
ovulated that release progesterone and
estrogen looking at these structures
histologically at a higher magnification
the outermost layer of the ovaries so
we're talking about even external to the
tunica alpha genia we see that there's
actually a single layer of simple
cuboidal cells that surround the ovarian
surface this structure is called the
germinal epithelium this is actually a
sorosal layer that drapes over the
ovaries and here the sorceal cells are
not squamous but instead are cuboidal to
columnar in shape so here's higher
magnification of the external surface of
the ovary we can see that here is that
loosely defined tunica albugenia and
outside of that we're seeing this simple
cuboidal epithelial tissue this is the
germinal epithelium aka the sorosaur
layer when this layer was first
discovered they were actually thought to
be the germ cells themselves that gave
rise to the oocytes hence the term
germinal epithelium which we now know is
actually not the case but unfortunately
this name kind of stuck around so it's
important to know that this germinal
epithelium is actually a misnomer in the
testes however there are also
histological structures called the
germinal epithelium but in the case of
testes the germinal epithelium is
actually an appropriate name since it is
actually referring to the structures
that produce the spermatocytes and that
will be highlighted in the male
reproductive system lecture the tunica
albuginea as mentioned before is an
ill-defined layer of dense irregular
connective tissue surrounding the outer
layer of the ovaries but now deep to the
germinal epithelium now during fetal and
childhood periods the ovarian cortex
about this region contains hundreds of
thousands of immature follicles called
the primordial follicles in the
background of ovarian stroma so the
primordial follicles would be the
majority type of follicles we would see
before puberty however starting at
puberty when the hypothalamus starts to
release the gonadotropin releasing
hormones or the gnrh the basophils in
the anterior pituitary will start to
secrete the follicle stimulating hormone
or the fsh which then starts to simulate
several follicles every month to start
to grow so as a result during the
reproductively active years a variety of
follicles in different stages of growth
are observed in the ovarian cortex and
based on some characteristic
morphologies and based on some
characteristic morphologies there are
different types of identifiable ovarian
follicles that are called different
names such as the uni laminar primary
follicle multilaminar primary the antral
or the secondary follicles and the
mature or graphene follicles and the
atretic follicles so let's look at each
one's histology a little closer the
primordial follicle is something like
this
these and as the name suggests these are
the most immature forms of follicles
that actually formed during the
embryonic period and stuck around the
primordial follicle is comprised of the
primary oocyte which is the spherical
cell with large cell cytoplasm and
nucleus and the primary oocyte is
actually arrested at prophase one of
meiotic cell division so it may still
contain the nucleus with intact nuclear
envelope but we may see some thready
chromosomes that have condensed and are
waiting to separate such primary oocyte
in the primordial follicle is surrounded
by a single layer of flattened ovarian
stromal cells called the follicular
cells which provides supportive roles
for the primary oocytes the uni laminar
primary follicles are essentially the
primordial follicles that have started
to grow under the influence of follicle
stimulating hormone so the uni laminar
primary follicles are characterized by
the larger size of the primary oocytes
so here is the oocyte that has grown a
bit in size here's the primordial
follicle with the primary oocyte for
comparison and at this stage in
follicular growth the flattened
follicular cells have actually
transformed into a cuboidal histology so
the primary oocytes in the unilaminar
primary follicles are surrounded by a
single layer of larger follicular cells
at which point the follicular cells are
now called the granulosa cells and here
is another uni-laminar primary follicle
that is surrounded by a single layer of
cuboidally shaped granulosa cells note
also the ovarian stroma the connective
tissue component of the ovary is
actually quite cellular and as the
follicles start to grow the stromal
cells themselves especially the ones
that are immediately surrounding the
follicles will kind of arrange
themselves into
spherical conformation and later on
these stromal cells too will start to
provide some supportive roles as well
now the continued growth of the
follicles under the fsh influence will
result in a more mature form of
follicles called a multi-laminar primary
follicle here the primary oocyte is
getting larger still and we didn't quite
catch the nucleus here and this probably
has more to do with the plane of suction
than the fact that this cell is lacking
the nucleus since the oocytes are quite
large cells at any rate the oocytes
themselves start to accumulate this
acellular barrier on its external
surface called the zona pellucida which
directly translates to the pale zone
this structure plays an important role
in blocking out the spermatocytes from
directly entering the oocyte now outside
the zona pellucida the granulosa cells
themselves have undergone quite a bit of
proliferation so as opposed to having a
single layer of cuboidal granulosa cells
we now have multiple layers hence the
name the multilaminar primary follicle
another thing that is noticeable here is
the clear boundary between the outermost
layer of the granulosa cells and the
surrounding stromal cells and the
stromal cells that are immediately
outside this boundary start to actually
enlarge and form a layer of capsule-like
structure called the thicker layer so
this would be the thicker layer that is
comprised of the stromal cells and
around at this point the stromal cells
that are immediately outside this
basement membrane start to secrete the
precursors of estrogen called the
angiosynodone for the granulosa cells to
convert to the proper estradiol which
would then be released into the
bloodstream to stimulate the uterine
endometrial growth so as the follicle
itself is growing it is starting to
release these hormonal products that the
uterine glands can respond to the
continued growth of multi-laminar
primary follicles leads to this
structure called the anterol or the
secondary follicle which is
characterized by these fluid-filled
spaces that start to accumulate within
the granulosa cells so again
enterofollicles have the primary oocytes
that are arrested at the prophase one of
meiosis they have still the zona
pellucida that is surrounding the
outside of the oocyte and then we have
the multiple layers of granulosa cells
but this time we have these fluid-filled
spaces that'll start to eventually kind
of coalesce into bigger and bigger
fluid-filled spaces as the follicle
itself grows what's interesting also is
that as the follicles are growing they
start to move towards the medulla of the
ovary where the source of vasculature
and fluids are located in the form of
helicine arteries and veins another
unique feature about the enteral
follicles is that the this thicker layer
the stromal cells outside the granulosa
layer will start to differentiate into
the inner and the outer deca layer with
the dica internal layer being comprised
of a bit larger stromal cells and the
external layer deca externa being
comprised of more of a flattened stromal
cells that form an indistinct
capsule-like structure and these two
thicker layers will become more and more
distinct as the follicle itself grows
larger and larger nigentica interna has
the endocrine function of producing the
androcynodione which then the granulosa
cells can convert to the estradiol the
estrogen product that is released into
the bloodstream and now we have the
mature follicles this is the most well
developed and the largest of the
follicles that are characterized by a
single enlarged fluid filled space
called the antrum the oocyte is still a
primary oocyte that's arrested at
prophase one of meiosis
and at this point outside the granulosa
cell layer of this mature follicle we
can really see the distinctive deca
interna cells comprised of larger
spindle-shaped cells versus the tica
extrana which is comprised of the
flattened stromal cells that are
essentially forming an indistinct
capsule-like structure and the internal
aspect of the mature follicle we can see
that the outside of the zona pellucida
we have this layer of granulosa cells
that are forming kind of a protective
outer covering of the primary oocyte
this outer layer of granulosa cells are
collectively called the corona radiata
for resembling a radiating crown if you
will and then we can also see another
collection of granulosa cells that are
attaching this oocyte complex to the
rest of the granulosa cell layer on the
outer aspect of the follicle and this
region or structure is collectively
called the cumulus ovaries and as this
mature follicle also known as the
graafian follicle starts to enlarge this
growing follicles will actually start to
come back up towards the tunica virginia
towards the surface of the ovary in
preparation for the ovulation of this
oocyte complex and up until this point
the primary oocyte is still arrested in
prophase one but just before the
ovulation the oocyte is triggered to
finish meiosis 1 and enter meiosis ii
thus becoming a secondary oocyte but
even the secondary oocyte as the
ovulation occurs is arrested again at
meiosis ii at metaphase so once the
oocyte is ovulated this oocyte can now
be called the secondary oocyte it is
surrounded on the outside by the zona
pellucida as well as several layers of
granulosa cells aka the corona radiata
the secondary oocytes are arrested at
meiosis ii at metaphase and this meiotic
division will not finish until
fertilization is successfully achieved
now lastly the atritic follicles atresia
itself refers to the absence or
incomplete formation or even
degeneration so in the ovaries numerous
follicles at any stage of growth can
undergo atresia and this is actually
happening at all times from fetal stage
up until menopause so it is not uncommon
to observe atritic follicles or the ones
that are degenerating in the ovaries
especially the larger follicles that are
undergoing atresia are histologically
quite noticeable by the abundant signs
of apoptosis not only of the primary
oocytes but also of the numerous
granulosa cells so again the atritic
follicles are referring to the
degenerating follicles at various stages
of growth and they're recognized by the
science of apoptosis where the cell
membranes of the apoptotic cells are not
distinctive at all including even that
of the oocyte and some other signs of
apoptosis would be a lot of these
hypnotic or really condensed nuclei and
cellular debris and furthermore the
general tissue integrities of the
follicles are lost as the apoptotic
cells are essentially sloughing off and
floating into the antrum if you will so
again such atritic follicles are not at
all uncommon to see and observe in the
ovarian histology
now during reproductive years in
addition to a variety of follicles the
corpus luteum may be observed as well in
the ovarian cortex the corpus refers to
the body ludium or ludia refers to the
color yellow so corpus luteum literally
translates to the yellow body so this is
a yellow body of about one to two
centimeter diameter structure that can
actually be observed with naked eyes on
the ovarian cortex without the aid of
microscopes the corpus luteum is
actually formed by what's remaining of
the mature follicle after it has
ovulated or released the oocyte complex
into the peritoneum so this ill-defined
cellular structure in the corpus luteum
is comprised of the remaining granulosa
cells and the deca cells that have kind
of collapsed onto themselves at this
point the granulosa cells are called the
granulosa ludian cells and the tica
internal cells become the thicker ludian
cells the reason why the corpus luteum
appears as this yellow body under naked
eye observation is due to the rich
steroid hormones especially the
progesterone in addition to the estrogen
that are being secreted by the granulosa
lutein and dicaludian cells
the progesterone in particular that's
released by the corpus luteum plays such
an important role in signaling the
endometrial glands to not only stick
around but start to secrete glandular
fluids in anticipation of the fertilized
product to arrive into the uterus an
interesting fact about the corpus luteum
is that they naturally have about the
lifespan of 10 to 14 days to release the
progesterone and estrogen but in the
absence of fertilization and
particularly the placenta formation in
the uterus the corpus luteum will start
to degenerate after about 14 days and
with their involution or degeneration
the uterine endometrial glands will
start to shed resulting in menstruation
and as the corpus luteum itself
degenerates numerous macrophages and
fibroblasts will come in and replace
this structure with dense irregular
connective tissue scar thereby becoming
the corpus albicans or the white bodies
in case of successful fertilization and
the implantation of the conceptus in the
uterus however there's this developing
placenta that'll start to secrete the
human chorionic gonadotropin or the hcg
and hcg will actually signal the corpus
luteum to persist in fact not only
persists but also to proliferate and
really crank up the production of
progesterone in addition to the estrogen
in order to sustain the uterine
endometrial glands so the corpus luteum
ends up sticking around and growing for
up to about five months into pregnancy
in fact the corpus luteum during
pregnancy can get quite large it can
hypertrophy
quite significantly to about half the
size of the ovary itself it's quite
remarkable but after about five months
the placenta itself can start to produce
its own progesterone and estrogen level
and at that point the corpus luteum can
start to ingress and eventually
degenerate so the corpus albicans or
corpora albicansia in plural are what
remains after corpus luteum degenerates
and becomes replaced with the scar
tissue so histologically the corpus
albicans looks like dense irregular
connective tissue with lots and lots of
collagen type 1 fibers and flattened
fibrocytes that are wedged in between
and albicans once again refers to the
color white which is attributable to the
grayish whitish collagen fibers that can
be observed with naked eyes so with
increasing age we can imagine how more
and more corpora ludia are forming than
degenerating therefore the number of
corpora albicans will start to
accumulate an increase in number with
age thank you for watching this video
from the da vinci academy histology
video course which is completely
available on youtube to access the
corresponding practice questions and
histology lab videos go to our website
using the link in the description below
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so
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you
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