Female Reproductive System - Menstrual Cycle, Hormones and Regulation

Summary

This educational video delves into the hormonal regulation of the female reproductive cycle, focusing on the menstrual cycle's complexity. It explains the role of the hypothalamus and pituitary gland in producing FSH and LH, which stimulate ovarian follicle maturation. The script outlines the two phases of the cycle: the follicular phase marked by rising estrogen levels and the luteal phase characterized by the formation of the corpus luteum and progesterone's role in preparing the uterus for potential fertilization. The video clarifies the feedback mechanisms of these hormones and their impact on the menstrual cycle's cyclical nature.

Takeaways

• 🧠 The hypothalamus and anterior pituitary gland play a central role in the hormonal regulation of the female reproductive cycle, producing key hormones like gonadotropin-releasing hormone (GnRH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH).
• 🌀 The menstrual cycle is divided into two phases: the follicular phase (first 14 days) and the luteal phase (last 14 days), each with distinct hormonal changes and physiological events.
• 📈 Estrogen levels initially have a negative feedback effect on LH secretion from the anterior pituitary, but at high concentrations, they trigger a positive feedback loop, leading to a surge in LH that induces ovulation.
• 🥚 Ovulation is the release of a mature egg (oocyte) from the ovary, which is triggered by a significant increase in LH levels during the menstrual cycle.
• 🔄 After ovulation, the ruptured follicle transforms into the corpus luteum, which secretes hormones like estrogen, inhibin, and progesterone, playing a critical role in the second half of the menstrual cycle.
• 🚫 Inhibin, produced by the corpus luteum, inhibits the secretion of FSH, preventing further follicle maturation during the luteal phase.
• 🛡 Progesterone, another hormone secreted by the corpus luteum, has a negative effect on the hypothalamus, inhibiting the release of GnRH and thus LH and FSH, preparing the body for potential pregnancy.
• 🌱 Progesterone stimulates the growth of the endometrial lining, which is necessary for the implantation of a fertilized egg.
• 🔻 If fertilization does not occur, the corpus luteum degenerates, leading to a decrease in progesterone, estrogen, and inhibin, which in turn allows for the onset of a new menstrual cycle.
• 🔄 The menstrual cycle is a continuous process, with the endometrial lining shedding during menstruation, paving the way for a new set of follicles to mature in the next cycle.
• 📊 Hormonal graphs provided in the script illustrate the dynamic changes in hormone concentrations throughout the menstrual cycle, highlighting the interplay between the hypothalamus, pituitary gland, and ovaries.

Q & A

What are the main hormones involved in the hormonal regulation of the female reproductive cycle?

The main hormones involved are gonadotropin-releasing hormone (GnRH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), estrogen, progesterone, and inhibin.

Which part of the brain regulates the release of hormones by the anterior pituitary gland in the female reproductive system?

The hypothalamus regulates the release of hormones by the anterior pituitary gland through the production of gonadotropin-releasing hormone (GnRH).

What is the role of FSH in the female reproductive cycle?

FSH stimulates the maturation of primary follicles in the ovaries and is involved in the production of estrogen by these follicles.

How does estrogen affect the secretion of luteinizing hormone (LH) at low concentrations?

At low concentrations, estrogen has a negative feedback effect on the pituitary gland, inhibiting the release of LH.

What triggers the ovulation of the most mature follicle in the ovary?

A massive spike in luteinizing hormone (LH) concentration triggers the ovulation of the most mature follicle.

What is the purpose of the corpus luteum after ovulation?

The corpus luteum secretes hormones such as estrogen, inhibin, and progesterone, which are crucial for the preparation of the uterine lining for potential fertilization.

How does the menstrual cycle divide into two phases?

The menstrual cycle is divided into the follicular phase (first 14 days) and the luteal phase (last 14 days).

What is the role of progesterone during the luteal phase?

Progesterone has several functions, including stimulating endometrial growth, inhibiting gonadotropin-releasing hormone (GnRH) secretion, and preventing further follicle maturation by inhibiting FSH secretion.

What happens to the endometrium if fertilization does not occur?

If fertilization does not occur, the corpus luteum degenerates, leading to a decrease in progesterone and estrogen, which results in the shedding of the endometrial lining, causing a period.

How does the decrease in progesterone and estrogen levels at the end of the menstrual cycle initiate a new cycle?

The decrease in progesterone and estrogen levels leads to the inability to inhibit GnRH release, causing an increase in GnRH levels, which in turn allows a new menstrual cycle to begin.

What is the significance of the negative feedback mechanism involving estrogen and LH during the first half of the menstrual cycle?

The negative feedback mechanism involving estrogen and LH helps to maintain a steady level of LH and prevents premature ovulation, ensuring that only one follicle matures and ovulates each cycle.

Outlines

00:00

🌟 Hormonal Regulation of the Female Reproductive Cycle

This paragraph introduces the complex hormonal regulation of the female reproductive cycle, focusing on the menstrual cycle. It begins with the hypothalamus and pituitary glands, explaining the role of gonadotropin-releasing hormone (GnRH) in stimulating the anterior pituitary to produce follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The video script outlines the journey of these hormones to the ovaries, where they stimulate the maturation of follicles and the eventual ovulation of an egg. The menstrual cycle is divided into the follicular phase and the luteal phase, with the first 14 days dedicated to follicle development and the latter 14 days to the formation and function of the corpus luteum. The script also discusses the hormonal changes depicted in a graph, illustrating the fluctuations in FSH, LH, and estrogen levels throughout the cycle.

05:02

🔍 The Dynamics of Estrogen and Hormonal Feedback Loops

The second paragraph delves into the role of follicle-stimulating hormone (FSH) in stimulating the maturation of primary follicles into secondary follicles within the ovaries. As these follicles mature, they produce estrogen, which has a negative feedback effect on the pituitary gland, inhibiting the release of luteinizing hormone (LH) at low concentrations. The script explains how FSH levels decrease as estrogen levels rise due to the negative feedback mechanism. It also highlights the importance of estrogen in the female body, comparing it to testosterone in males and detailing its effects on bone and muscle growth, endometrial growth, and maintenance of secondary sexual characteristics. The paragraph describes the shift from negative to positive feedback as estrogen levels peak around day 10 of the menstrual cycle, leading to a surge in LH that triggers ovulation. The release of the oocyte and the transformation of the follicle into the corpus luteum mark the transition to the luteal phase.

10:07

🌱 The Luteal Phase: Hormonal Changes and Endometrial Preparation

The final paragraph discusses the luteal phase of the menstrual cycle, characterized by the formation of the corpus luteum and its secretion of estrogen, inhibin, and progesterone. The script explains how inhibin inhibits the secretion of FSH, preventing further follicle maturation during this phase. Progesterone, the key hormone of the luteal phase, has a negative effect on the hypothalamus, inhibiting the secretion of gonadotropin-releasing hormone (GnRH), which in turn affects LH and FSH levels. Progesterone's main function is to stimulate endometrial growth, preparing the uterus for potential egg implantation. If fertilization does not occur, the corpus luteum degenerates, leading to a decrease in progesterone and estrogen levels, which allows for the shedding of the endometrial lining, known as menstruation. This marks the end of one cycle and the beginning of a new one, as GnRH levels rise to initiate the next menstrual cycle.

Keywords

💡Hypothalamus

The hypothalamus is a small region at the base of the brain that links the nervous system to the endocrine system via the pituitary gland. In the context of the video, it is crucial for the hormonal regulation of the female reproductive cycle as it produces gonadotropin-releasing hormone (GnRH), which initiates the menstrual cycle by signaling the anterior pituitary to release other hormones.

💡Pituitary Gland

The pituitary gland is an endocrine gland that controls various functions of the body through the secretion of hormones. The video script discusses the anterior pituitary's role in the female reproductive cycle, where it is stimulated by the hypothalamus to produce follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which are essential for follicle maturation and ovulation.

💡Follicle-Stimulating Hormone (FSH)

FSH is a hormone produced by the anterior pituitary gland that plays a key role in the development of ovarian follicles and the maturation of oocytes in the female reproductive system. The video explains that FSH levels rise at the beginning of the menstrual cycle, stimulating the maturation of primary follicles into secondary follicles, which produce estrogen.

💡Luteinizing Hormone (LH)

LH is another hormone produced by the anterior pituitary gland that triggers ovulation in the female reproductive system. The script describes LH's steady level during the early menstrual cycle and its critical surge that leads to ovulation around the midpoint of the cycle.

💡Menstrual Cycle

The menstrual cycle is a biological process that occurs in females involving the changes in the ovaries and the lining of the uterus over approximately one month. The video script outlines the hormonal regulation of this cycle, detailing the phases and hormonal changes that lead to ovulation and, in the absence of fertilization, menstruation.

💡Ovarian Follicles

Ovarian follicles are structures in the ovaries that contain immature oocytes (eggs). The video script explains that many follicles begin to mature at the start of the menstrual cycle, but typically only one will ovulate. The maturation process is influenced by hormones such as FSH and LH.

💡Estrogen

Estrogen is a primary female sex hormone that plays a crucial role in the development of female reproductive tissues and secondary sexual characteristics. In the video, estrogen is described as having both negative and positive feedback effects on the pituitary gland's hormone secretion, and it is produced by maturing follicles.

💡Ovulation

Ovulation is the release of a mature oocyte from the ovarian follicle, typically occurring around the midpoint of the menstrual cycle. The video script describes the LH surge that triggers ovulation, leading to the release of an egg that can be fertilized.

💡Corpus Luteum

The corpus luteum is a temporary endocrine structure in the ovary that forms after ovulation from the remnants of the ovarian follicle. The script explains that the corpus luteum secretes hormones like estrogen, inhibin, and progesterone, which are crucial for preparing the uterus for potential pregnancy.

💡Progesterone

Progesterone is a hormone that plays a key role in the menstrual cycle, particularly in preparing the uterine lining for the implantation of a fertilized egg. The video describes how progesterone levels increase after ovulation and its role in inhibiting the secretion of gonadotropin-releasing hormone, thus influencing the start of a new menstrual cycle.

💡Inhibin

Inhibin is a hormone produced by the ovaries that has a negative feedback effect on the secretion of FSH. The script mentions that inhibin levels increase after ovulation due to the corpus luteum, helping to prevent further follicle maturation during the luteal phase of the menstrual cycle.

💡Endometrium

The endometrium is the inner lining of the uterus that undergoes cyclic changes in response to hormonal changes during the menstrual cycle. The video script explains that progesterone stimulates the growth of the endometrium in preparation for potential implantation of a fertilized egg, and its shedding during menstruation signifies the beginning of a new cycle.

Highlights

The female reproductive cycle is more complex than the male's due to hormonal regulation.

The hypothalamus and anterior pituitary gland regulate the female reproductive hormones.

Gonadotropin-releasing hormone (GnRH) stimulates the production of FSH and LH in females.

FSH and LH travel to the ovaries to stimulate the maturation of follicles and egg production.

The menstrual cycle is divided into the follicular phase and the luteal phase, each lasting 14 days.

The initial increase in GnRH leads to a steady increase in FSH and LH, followed by a drop in FSH levels due to estrogen's negative feedback.

Estrogen levels rise as follicles mature, affecting the secretion of LH and FSH.

Estrogen has a dual role, inhibiting LH at low concentrations and stimulating it at high concentrations through positive feedback.

The surge in LH triggers ovulation, releasing the mature egg from the ovary.

After ovulation, the follicle transforms into the corpus luteum, which secretes estrogen, inhibin, and progesterone.

Inhibin inhibits FSH secretion to prevent further follicle maturation during the luteal phase.

Progesterone plays a crucial role in the luteal phase, inhibiting GnRH and LH secretion, and stimulating endometrial growth.

The corpus luteum degenerates at the end of the cycle, leading to a decrease in hormones and the onset of a new menstrual cycle.

The decrease in progesterone and estrogen cannot maintain the endometrium, resulting in its shedding, known as menstruation.

The menstrual cycle's hormonal regulation is essential for understanding female reproductive health and fertility.

The video provides a comprehensive overview of the hormonal regulation of the female reproductive cycle, aiding in educational and practical applications.

Transcripts

Armando Hasudungan biology and medicine videos

Please make sure to [subscribe] join the forum in group for the latest videos please visit Facebook Armando Hasudungan

In this video we will look at the hormonal regulation of the female reproductive cycle

so we will be looking at the menstrual cycle basically and

Yes, so the menstrual cycle

the Hormones of

the female is

So much more complicated the Male's

but hopefully we'll be able to understand it by the end of this video, so

[we] begin with the hypothalamus and the pituitary glands which are made up of the anterior and posterior pituitary glands

We'll be focusing on the anterior pituitary gland the hypothalamus regulates hormones released by the anterior pituitary

through the portal blood here in

The female reproductive system the hypothalamus produces a hormone called gonadotropin-releasing hormone

which will travel here to the anterior pituitary via the portal blood and

It will cause the cells in the anterior pituitary gland to produce two important hormones

known as

FSH, follicle stimulating Hormone and LH luteinizing hormone

Please note that in males this same process also occurs Males also produce

Gonadotropin releasing hormone which will

Cause the anterior pituitary to release

Luteinizing hormone and follicle stimulating hormone, so what will these hormones do in the female body?

Well these hormones will travel to the female ovaries where the female eggs are produced

So let's just recap quickly. What the ovary is and where it is. So here. We have the uterus and

the Ovaries

Which connects to the Uterus via the Fallopian Tube essentially

But it's now known as a uterine tube so we [will] focus on this over here, so let's zoom in

so here is the ovary and

it has blood vessels and

This and it's through these capillaries these blood vessels that the hormones can enter

Now in each ovary there are follicles

Women have many many follicles in the ovaries and each month only some will begin to mature

But only one will ovulate and become essentially will ovulate and produce an egg

Now let's just say it's the beginning of the menstrual cycle. So just after female has shed her uterine wall just had the period

now within the ovaries females have many many many primordial follicles and

Each month only some of these primordial follicles will mature

Into primary Follicles, and they will keep maturing but only one will ovulate

So here. I'm drawing one primary follicle, and it's the beginning of the menstrual cycle

Before we continue on let's look at the let's look at the changes [of] the hormone concentrations

That come from the brain by looking at a graph

so

here we have a y-Axis which shows the concentration of the hormones in blood and

On the [x-axis] is a duration of the female menstrual cycle which normally goes for about 28 days

So the dotted line in the middle is 14 days. Which is halfway

Now just to simplify things even more the menstrual cycle can be divided into two phases

the first 14 days is known as the follicular Phase and

the Last 14 days

Is known as the luteal phase and this is important to keep in mind, so the first is the follicular Phase

II is the luteal Phase

Now initially in the beginning of the menstrual cycle there is an increase in Gonadotropin releasing hormone secreted by the hypothalamus

because it's the start of the menstrual cycle and

this should cause a steady increase in Follicles stimulating hormone and

luteinizing hormone

but instead we see a

Increase and then a slow

Dropping level of follicle stimulating hormone, and we have a steady level of luteinizing hormone

Why is this?

Well the reason is actually quite complicated, but just hold on to that thought and hopefully it'll make sense

So let's go back to the ovary

So follicle stimulating hormone

Will initially rises remember?

Because the follicular phase is the first phase of the menstrual cycle

Follicle stimulating hormone will enter the ovaries and what they will essentially do is stimulate it will stimulate

follicle Maturation of these

primary Follicles and

so some of these primary follicles will mature into

A secondary follicle, I'm only drawing one secondary follicle for simplicity

While these follicles are maturing they produce another hormone called Estrogen

Now Estrogen has many effects in

the first ten days of the menstrual cycle

So in the beginning estrogen has a negative feedback on the pituitary gland inhibiting the release of luteinizing hormone

To put it simply at low concentrations estrogen inhibits luteinizing hormone secretion from the anterior pituitary

And that is why we only see a steady level of luteinizing hormone in the blood

Because even though gonadotropin-releasing hormone

from the hypothalamus is stimulating the release of luteinizing hormone at

low

concentrations estrogen will inhibit

luteinizing hormone release

Another fact is that follicle stimulating hormone is secreted

primarily in response to Low Estrogen

concentrations, so when Estrogen levels rise

Follicle stimulating hormone levels will fall and that is why we see in the graph a steady drop in

Follicle stimulating hormone because there's a increase in Estrogen levels from the follicles

So let's draw another graph and see the concentrations of the hormones produced by the ovaries during the menstrual cycle

Which goes on for 28 days

So as the follicle matures they will produce more estrogen

which as I mentioned at low concentrations estrogen will inhibit the secretion of luteinizing, hormone and

Also the increase in estrogen concentrations will cause a decrease in Follicle stimulating hormone secretion

Estrogen is an important hormone

Especially for females because Estrogen is basically males equivalent of testosterone, Estrogen

Peripheral effects include stimulating bone and muscle Growth it stimulates endometrial growth

Maintains female Secondary characteristics and maintains a female the glands the breasts amongst many other things

So just to draw this graph up to

Ten days of the Menstrual cycle. We see a steady a steady

low concentration of luteinizing Hormone due to the inhibitory effects of estrogen remember in the first ten days and

We also see a steady drop of follicle stimulating hormone due to the increase in estrogen levels as well. Which has a negative feedback

So what happens after 10 days?

well after 10 days estrogen levels will continue to rise as the follicles mature in the ovaries and

After 10 days as estrogen levels rise. It will have a positive Feedback and

It will stimulate the release of luteinizing hormone

so at low concentrations estrogen will inhibit luteinizing hormone secretion however at

High concentrations, Estrogen will stimulate luteinizing hormone secretion

Now things are changing

the increase in gonadotropin releasing hormone and estrogen will stimulate

then luteinizing Hormone secretion

And you see this massive spike in luteinizing hormone concentration

It's this massive

luteinizing Hormone concentration that will trigger

ovulation of the Most Mature Follicle in the ovary

The ovulation of the follicle will release what we know as the female egg the oocyte

or Oocyte

After ovulation the luteinizing hormone levels will drop back down

gonadotropin releasing Hormone will slowly drop as well

follicle stimulating hormone also had a small spike as a side effect of the surge of luteinizing hormone release

so luteinizing Hormone triggers ovulation and

oocyte is released after

The Follicle ovulates the follicle will turn into a corpus luteum which is a dead follicle, basically

Now that is why the first 14 days of the menstrual [cycle] is called the follicular Phase

Because it all has [to] do with the follicles and its maturation and the last 14 days is known as the luteal phase

Because we have the formation of the corpus luteum

The corpus luteum will essentially slowly degrade

However it also has a purpose it in that it secretes hormones. It secretes three hormones estrogen again

inhibin and Progesterone

So what we see in the concentration levels of these Ovarian hormones

Estrogen will increase until

ovulation and then drop slightly

Inhibin was not present until after ovulation then it begins to increase thanks to the corpus luteum

Progesterone levels will were low until after ovulation during the luteal phase

so at

21 days of the female reproductive cycle progesterone is increasing inhibin is increasing and

Estrogen is still detectable and all these hormones are all produced. Thanks to the corpus luteum

So what do these hormones do?

Well inhibin has a negative feedback

And it will essentially inhibit the secretion of follicle stimulating hormone because we are at the luteal Phase

We don't need any more follicles to mature just yet

So that is why inhibin is preventing follicle stimulating hormone release to prevent follicle maturation

So here. I wrote as the secondary corpus luteum develops inhibiting secretion will suppress follicle stimulating hormone

release

Progesterone is the most

important Hormone in

The Luteal phase and has many functions [one] of which is having a negative effect on the hypothalamus

inhibiting the secretion of gonadotropin releasing hormone

Now after ovulation during the luteal phase

The progesterone levels will increase slowly and the estrogen levels will decrease

Slowly kind of and this will suppress gonadotropin releasing hormone release

and

So progesterone will inhibit gonadotropin releasing hormone release

Which will also [effect] the release of luteinizing hormone and follicle follicular stimulating hormone?

So during the luteal phase as progesterone and inhibin increase

This will essentially cause a decrease in

gonadotropin releasing Hormone, luteinizing Hormone and follicular stimulating hormone

But the main effect of progesterone is that it will stimulate endometrial growth

the endometrial lining is the lining of the uterus which will shed each month or

Or the endometrium is where the egg?

Will implant if it's fertilized

by sperm

okay, let's just say there was no fertilization because this is just a normal menstrual cycle and

Of course all good things have to come to an end the corpus luteum in the ovary will degenerate

allowing a new set of Follicles to mature

So as the corpus luteum degenerates all these hormones that are that were produced by the corpus luteum

the estrogen, inhibin and progesterone, they will decrease like so

so when the corpus luteum degenerates

Progesterone will Decrease and

this will mean that progesterone cannot inhibit gonadotropin releasing hormone release and

So gonadotropin releasing hormone levels will increase and this will allow a new menstrual cycle to occur

also

because of the decrease in Progesterone and estrogen in part

means that these hormones cannot maintain the endometrium the endometrial lining in the uterus and

so the endometrium will shed and this is known as the period and

After the endometrial lining sheds this allows a new cycle to occur and though

And then you see a increase in gonadotropin releasing hormone again and the cycle continues

Hope you enjoy this video. Thank you