Ovarian Follicle在线视频

Hello, everyone!

Today we will discuss the

female ovarian follicles.

First,

let's see a case.

18-year-old Rose

had irregular menstrual menstrual cycle

since her menarche.

Rose realized it might be abnormal

for a woman and went to see the doctor.

Ultrasound examination indicated that

there was follicular maldevelopment

in Rose's ovaries.

The question from Rose was

"What are the possible reasons

and influences of my ovarian

follicular maldevelopment?"

To answer Rose's question

you should first be able to

list the main functions of the ovary

describe the morphological features

of ovarian follicles

in different developing stages

and then explain some possible

mechanisms for ovarian disorders

in patients like Rose.

These are also the learning objectives

of this session.

Shown in this picture are the organs

of the female reproductive system.

The ovary is the female gonad

with two functions

production of oocytes

and secretion of sex hormones.

In the female pelvic cavity

the ovary is attached

to the broad ligament

through which vessels

and nerves pass to

and enter at the hilum of the ovary.

At the hilum

besides the blood vessels and nerves

there is another kind of

secretory cells

hilar cells.

These cells can produce androgen

in the female.

Do you still remember

what is the function of androgen

in the female?

Can you summarize the types of the cell

which can produce androgen

since their dysfunction

will result in endocrine disorders?

This is the light microscopic cross

section of the ovary under low power.

The parenchyma of ovary

is divided into an outer cortex

and an inner medulla.

The medulla is composed of loose

connective tissue.

The cortex consists of a very cellular

connective tissue stroma

in which the ovarian follicles

in different developing stages

are embedded.

Though the development of follicles

represents a morphological continuum

we are used to assign them

into 4 stages:

primordial follicles

primary follicles

secondary follicles

and mature follicles.

Among them

the primary and secondary follicles

are undergoing growth

hence also named growing follicles.

No matter what stages they are at

each ovarian follicle

consists of one oocyte

and surrounding follicular cells.

Now let's start from the beginning

primordial follicles

to see the development of the

ovarian follicles.

Primordial follicles are the smallest

and most abundant follicles.

The oocyte is the center

of the follicle.

It is about 30μm

and the size is obviously larger

than the surrounding follicular cells.

The key to identify the

primordial follicles is the single layer

of flattened follicular cells.

In the adult ovary

the primordial follicles are commonly

aggregated in groups

and located in the cortex

just beneath the capsule.

The primordial follicles

are formed about the 5th month

of fetal life

and the oocyte at that time

enters the first stage of meiosis.

They will arrest right there

and maintain this status from fetal life

to puberty of the female

without proliferation

and differentiation.

At puberty

under the influence of the follicle

stimulating hormone (FSH)

secreted by the anterior pituitary

the primordial follicles

start to develop in batches

to primary follicles.

The follicular cells

change from flat to cuboidal

from one layer to multi-layers.

Their cytoplasm may have

a granular appearance

and they are for this reason

also called granulosa cells.

As the follicles continue to develop

a thick amorphous layer is visible

between the oocyte and granulosa cells.

This is the zona pellucida.

Zona pellucida is the pink line

in H&E-stained slides

and mainly consists of glycoproteins.

Both the oocyte and follicular cells

are believed to contribute to

the synthesis of the zona pellucida.

Since the follicles begin to grow

only after puberty

the antigenic property of the newly

expressed zona pellucida protein

would affect the immune system

if the glycoproteins come into contact

with the immune cells by accident.

In fact

some women with difficulty to conceive

do possess zona pellucida antibodies.

This is considered to be the

possible reason for some

ovarian follicular maldevelopment

and infertility.

At the late stage of the

primary follicles development

small fluid-filled spaces appear

between the follicular cells

as the follicle reaches a diameter

of about 400μm.

In the beginning

these are small and can be seen

in different places

between the follicular cells.

Finally,

all these small fluid-containing spaces

will fuse to form

a large follicular antrum

filled with follicular fluid.

The follicular antrum

is the distinguishing feature

of the secondary follicle.

So,

you can also call it

a vesicular follicle.

In vesicular follicles,

the granulosa cells immediately

surrounding the zona pellucida

become elongated

and make up the corona radiata.

As the follicles develop

and enlarge in size

the surrounding stromal cells

form an organized theca

around the follicle.

In secondary follicles,

it is easy to identify the follicular theca

containing 2 layers

theca interna and theca externa.

This picture shows part of the wall

of the secondary follicle.

Theca interna cells are polyhedral

and pale stained steroid-secreting cells.

Under the influence of FSH

from the pituitary

theca interna cells synthesize

androstenedione

which will be transported

into the cytoplasm of

adjacent follicular cells.

The enzyme aromatases

in the follicular cells

transform the androstenedione

into estrogen.

This is how the female sex hormone

estrogen is produced.

The theca externa is derived from

spindle-shaped stroma cells

with the potential to contract

during ovulation after the follicle

comes to the mature stage.

On about the 14th day

of the menstrual cycle,

one of the secondary follicles

in the ovary develops into

a very big structure in size.

Before ovulation

the oocyte finishes the first meiosis

and becomes a secondary oocyte.

This forms the mature follicle.

Please note that

we only have primary oocyte

in primordial follicles

primary follicles

and secondary follicles.

This is because before it

comes to the mature stage

there is no cell cycle change

for the oocyte

just follicular cells proliferation

during the growth of the follicle.

Only when the follicle develops

into the mature stage

the oocyte finishes its first meiosis

and becomes a secondary oocyte.

The mature follicle reaches

a diameter of 20-25 mm

and bulges under the ovarian surface.

Due to its large size

it is easy for us to monitor it

by ultrasound examination in the clinic.

Prior to ovulation

the secondary oocyte

zona pellucida

and corona radiata

dissociate from the follicular wall.

Due to the contraction of the theca externa

and the pressure within the

follicular antrum

the thin follicular wall will rupture

and the ovum is released from the ovary.

So

the mature follicle ends

in the release of a secondary oocyte

producing the female gamete

for fertilization.

Now is the summary on the development

of the ovarian follicles.

They are composed of 2 kinds of cells

and there are 4 stages

for follicular development.

During the developmental process

the female hormone estrogen

is produced.

A mature follicle will release

an ovum for fertilization.

These two main functions of ovary

are carried out by the development

of follicles in the ovarian cortex.

If there is a maldevelopment

of follicles

this will result in dysfunction

of female hormone secretion

and reproduction.

These are the references

for this session.

Thank you for your attention!