Female Reproductive Cycles Made Easy!

Summary

Dr. Mike's video offers an in-depth look at the female reproductive cycle, detailing the ovarian and endometrial cycles. It explains the development from primordial to mature follicles and the crucial role of hormones like estrogen and progesterone. The video also covers the phases of the uterine lining, from menses through the proliferative and secretory phases, and the significance of ovulation around day 14. It concludes with the importance of implantation and the impact on the menstrual cycle.

Takeaways

• 🔬 The female reproductive cycle is approximately 28 days long, encompassing both the ovarian and endometrial cycles.
• 🌱 The ovarian cycle involves the development and maturation of the egg, starting from a primordial follicle to a mature follicle that ovulates.
• 🌡️ Hormones play a crucial role, with follicle-stimulating hormone (FSH) and luteinizing hormone (LH) being key in regulating the cycle.
• 📈 Estrogen levels rise as the follicle matures, providing negative feedback to the hypothalamus to regulate FSH and LH release.
• 📉 A surge in LH, often 24 hours before day 14, triggers ovulation, where the mature egg is released from the follicle.
• 🌕 The luteal phase follows ovulation, characterized by the formation of the corpus luteum, which produces progesterone to prepare the uterus for implantation.
• 🩸 The endometrial cycle includes the menstrual phase (bleeding), the proliferative phase (thickening of the endometrium due to estrogen), and the secretory phase (further development due to progesterone).
• 💧 The endometrium's thickness and vascularization increase during the proliferative and secretory phases to facilitate potential implantation of a fertilized egg.
• 🔄 If fertilization and implantation do not occur, the cycle resets as progesterone levels drop, leading to the sloughing of the endometrium and the start of a new menstrual cycle.
• ⏰ The timing of ovulation and the window of implantation are critical for conception, with the endometrium remaining thickened and receptive for approximately 10 days post-ovulation.

Q & A

What are the two major cycles that make up the female reproductive cycle?

The two major cycles that make up the female reproductive cycle are the ovarian cycle and the endometrial cycle.

How long does the average female reproductive cycle last?

The average female reproductive cycle lasts from 0 to 28 days, although it can vary between 25 to 34 days.

What happens during the follicular phase of the ovarian cycle?

During the follicular phase, the primordial follicle matures into a primary, secondary, and then a mature follicle, which eventually ovulates.

What is the role of the zona pellucida in the process of fertilization?

The zona pellucida is a protective layer surrounding the egg that plays a crucial role in fertilization by allowing sperm to penetrate but preventing further sperm entry once fertilization occurs.

Which hormones are primarily responsible for the follicular phase of the ovarian cycle?

The hormones primarily responsible for the follicular phase are Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH).

Why do estrogen levels initially inhibit FSH and LH, and then later stimulate them?

Initially, estrogen levels inhibit FSH and LH to prevent the over-stimulation of follicles. Later, as estrogen levels rise significantly, they stimulate FSH and LH, leading to a surge in LH that triggers ovulation.

What is the significance of the LH surge that occurs just before ovulation?

The LH surge is significant because it triggers the final maturation of the follicle and the release of the egg during ovulation.

How does the endometrial cycle prepare the uterus for implantation?

The endometrial cycle prepares the uterus for implantation by going through the proliferative phase, where the endometrium thickens due to estrogen, and the secretory phase, where it becomes more vascularized and glandular due to progesterone.

What happens if fertilization and implantation occur during the female reproductive cycle?

If fertilization and implantation occur, the developing embryo releases human chorionic gonadotropin (hCG), which signals the corpus luteum to continue producing progesterone, maintaining the thickened endometrium and preventing menstruation.

What is the role of progesterone during the luteal phase?

During the luteal phase, progesterone is produced by the corpus luteum to maintain the thickened endometrium, creating a suitable environment for potential implantation of a fertilized egg.

Outlines

00:00

🌱 Overview of the Female Reproductive Cycle

Dr. Mike introduces the female reproductive cycle, emphasizing the interplay between the ovarian and endometrial cycles. He outlines the cycle's duration, typically 28 days but variable, and highlights the key events within the ovary and uterus. The discussion includes the development of egg cells, the role of hormones, and the preparation of the uterus for implantation.

05:01

🔬 Ovarian and Endometrial Cycles in Detail

This section delves into the two phases of the ovarian cycle: the follicular phase, where egg cells develop and are protected by follicles, and the luteal phase, post-ovulation. The video explains the transformation from primordial to mature follicles and the critical role of hormones like estrogen. It also touches on the hormonal regulation by the hypothalamus and anterior pituitary gland, focusing on follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

10:01

📈 Hormonal Dynamics and Ovulation

The paragraph discusses the hormonal fluctuations during the female reproductive cycle, particularly the feedback mechanisms involving estrogen, FSH, and LH. It explains how estrogen levels initially inhibit and later stimulate these hormones, leading to the LH surge that triggers ovulation. The paragraph also covers the formation of the corpus luteum and its function in producing progesterone, which is crucial for the luteal phase.

15:02

🩸 Menstrual Cycle Phases and Endometrial Changes

Dr. Mike describes the three phases of the endometrial cycle: menses (bleeding), proliferative (thickening of the endometrium due to estrogen), and secretory (preparation for implantation due to progesterone). The paragraph explains how hormone levels affect the endometrial lining's thickness and function, and the importance of the implantation window for a fertilized egg.

20:05

🌟 Implantation and the Beginning of a New Cycle

The final paragraph addresses the outcome of ovulation and the potential for fertilization and implantation. It explains how the presence or absence of a fertilized egg influences the continuation or termination of the menstrual cycle. The discussion includes the role of human chorionic gonadotropin (hCG) in maintaining the corpus luteum and the subsequent production of progesterone, which supports the early stages of pregnancy or leads to the start of a new cycle if implantation does not occur.

Keywords

💡Female Reproductive Cycle

The female reproductive cycle is a complex process that involves a series of hormonal and physiological changes leading to the maturation and release of an egg, and preparation of the uterus for potential fertilization and implantation. In the video, Dr. Mike explains that this cycle is typically 28 days long, with variations, and encompasses both the ovarian and endometrial cycles, which are crucial for understanding the overall process of reproduction.

💡Ovarian Cycle

The ovarian cycle refers to the series of changes that occur in the ovaries, including the development and maturation of follicles that house the egg cells. As Dr. Mike describes, this cycle involves follicular genesis, where the egg cells replicate and are nourished, and ovulation, where a mature egg is released. The ovarian cycle is marked by the development from a primordial follicle to a mature follicle, which then ovulates, and the formation of the corpus luteum.

💡Endometrial Cycle

The endometrial cycle pertains to the changes in the lining of the uterus, known as the endometrium, which prepares it for the potential implantation of a fertilized egg. Dr. Mike outlines three phases within this cycle: the menstrual phase, where the lining is shed; the proliferative phase, where the lining thickens due to estrogen; and the secretory phase, where the lining is further prepared for implantation, largely due to progesterone.

💡Hormones

Hormones play a central role in regulating the female reproductive cycle. Dr. Mike discusses the significance of hormones such as estrogen, progesterone, follicle-stimulating hormone (FSH), and luteinizing hormone (LH). These hormones are responsible for stimulating the development of follicles, ovulation, and the preparation of the endometrium, as well as providing feedback loops to the brain to regulate the cycle.

💡Follicular Phase

The follicular phase is the first phase of the ovarian cycle, during which the follicles develop and mature. As explained in the video, this phase is marked by a rise in FSH, which stimulates the growth of follicles. The follicular phase is crucial for the selection of a dominant follicle that will eventually ovulate, and it is during this phase that estrogen levels rise, influencing the endometrial cycle.

💡Luteal Phase

Following ovulation, the luteal phase begins, during which the remnants of the follicle transform into the corpus luteum, a structure that produces progesterone. As Dr. Mike explains, the luteal phase is characterized by high levels of progesterone, which is essential for maintaining the endometrial lining for potential implantation. If fertilization and implantation do not occur, the corpus luteum degenerates, leading to a drop in progesterone and the onset of menses.

💡Ovulation

Ovulation is the release of a mature egg from the ovary, typically around day 14 of the cycle. In the video, Dr. Mike emphasizes that ovulation is triggered by a surge in LH, which is a critical event in the reproductive cycle. The ovulated egg then enters the fallopian tube, where it may be fertilized by sperm, and if fertilization occurs, it will travel to the uterus for potential implantation.

💡Menstrual Phase

The menstrual phase, or menses, is the period of bleeding that marks the start of a new reproductive cycle. As described by Dr. Mike, this phase occurs when hormone levels drop, leading to the shedding of the endometrial lining. It signifies the end of one cycle and the beginning of another, preparing the body for the next opportunity for fertilization and implantation.

💡Estrogen

Estrogen is a hormone that plays a pivotal role in the female reproductive system. In the video, Dr. Mike explains that estrogen is produced by the granulosa and theca cells of the developing follicles. It is responsible for the thickening of the endometrium during the proliferative phase and has a feedback effect on the hypothalamus and pituitary gland, regulating the release of FSH and LH.

💡Progesterone

Progesterone is another key hormone in the female reproductive cycle, produced by the corpus luteum after ovulation. As Dr. Mike discusses, progesterone is essential for the secretory phase of the endometrial cycle, where it prepares the endometrium for implantation. It also has a luteoprotective effect, maintaining the corpus luteum and preventing menses if implantation occurs.

Highlights

The female reproductive cycle is composed of two major cycles: the ovarian cycle and the endometrial cycle.

The cycle typically spans from 0 to 28 days, with variations possible between 25 to 34 days.

The ovarian cycle involves the development and maturation of the egg, including follicular genesis and ovulation.

The endometrial cycle prepares the uterus for implantation through various hormonal changes.

The follicular phase of the ovarian cycle occurs from day 0 to day 14, marked by the development of the egg.

The luteal phase follows ovulation, from day 14 to day 28, where the corpus luteum produces progesterone.

Follicle-stimulating hormone (FSH) is crucial for the development of follicles into mature eggs.

Luteinizing hormone (LH) surges just before ovulation, triggered by high estrogen levels.

Estrogen levels rise during the follicular phase, providing negative feedback to regulate FSH and LH.

The endometrial lining undergoes three phases: menstruation, proliferation, and secretion.

Menstruation involves the shedding of the uterine lining, typically lasting about 5 days.

The proliferative phase is driven by estrogen, thickening and vascularizing the endometrium.

The secretory phase is influenced by progesterone, preparing the endometrium for potential embryo implantation.

If fertilization and implantation occur, the corpus luteum continues to produce progesterone, preventing menstruation.

The absence of implantation leads to a drop in progesterone levels, resulting in menstruation and the cycle restarting.

Human chorionic gonadotropin (hCG) is produced if implantation occurs, signaling the corpus luteum to maintain progesterone production.

Transcripts

hi everyone Dr Mike here in this video

we're taking a look at an overview of

the female reproductive cycle we're

going to take a look at what's happening

at the ovary what's happening at the

uterus what's happening in regards to

all the various hormones that are being

released and a lot more let's take a

look now to begin we need to understand

that the female reproductive cycle is

actually two major Cycles it's what's

happening inside the OV so the ovarian

cycle but also what's happening at the

uterus so the endometrial cycle both of

these two things are super important so

we're going to take a look at the

ovarian and uterine cycle and the

various changes that occur associated

with each and we're going to have a look

at the various hormones associated with

these changes as well now to begin we

need to understand that the ovarian and

uterine Cycles or the femal reproductive

cycle goes from 0 days to 28 days now

this is an approximate it can be lower

it can be higher but only by a little

bit it could probably be as low as 25

days and as high as 34 is days but it's

variable the average is 0 to 28 so we're

taking a look at the 0 to 28 female

reproductive cycle first of which is the

ovarian cycle so remember that there are

many things happening in the ovaries

what's happening is that this is where

our uyes are our egg cells now this is

where the genetic material resides and

this genetic material needs to replicate

it needs to undergo two phases of

meiosis but it also needs to be

nourished and protected and so this is

what's happening in the ovarian cycle is

follicular Genesis which is the

development of the follicles that

protect the egg but then also what

happens after the egg is ovulated we're

going to have a look at the endometrial

cycle as well so this is what's

happening at the uterus to prepare it

for implantation and the hormones

ovarian cycle to begin with there are

two major phases associated with the

ovarian cycle the first phase is that of

what we call the folicular

phase the follicular

phase the second phase is what we call

the luteal

phase the

luteal

phase now as you can see because we've

broken it up in accordance with days

here that from 0 to 14

we have the folicular phase and then

from day 14 to 28 we have the luteal

phase let's take a look at this to begin

with because the follicular phase is

associated with taking the uite or the

egg for example so here's the uite or

egg in a primordial form now that

primordial uite will turn into a primary

uite and this primary uite and I'm not

going to write that up yet this primary

oite is surrounded by a thin layer of

cells and this thin layer of cells we

call pregranulosa

cells pregranulosa

cells and the whole thing with the

pregranulosa cells and

the uite and this is called a

primary

uite this is called a

primordial follicle

primordial follicle now this primordial

follicle will start to mature and

develop and over time what's going to

happen throughout this follicular phase

so going from day Zer to day 14 is this

primordial follicle will get that

oite and those pregranulosa cells will

turn into granulosa cells more

cuboidal shaped cells and the uite will

be surrounded by this thing called a

Zona

paluca which helps prot protect it and

is very important when it comes to

fertilization once the sperm gets into

that zone of paluca it's like the screen

doors of the house all shut and don't

let any more sperm in so now we've got

these

granulosa granulosa cells and we've got

the zon of

paluca as well zon of

paluca and this is what we call a

primary follicle so it goes from a

primordial follicle to a primary

follicle now this whole time it's still

a primary uite so don't get that

confused even though the follicle name

changes it goes from a primary follicle

into a secondary

follicle and the secondary follicle is

very similar still has the zone of

paluca except there's one major change

well a couple first of which is you can

have a couple of layers of granulosa

cells so I'm just going to draw it up

like this and you're going to have some

additional cells called ther cells so

you have these ther cells now on the

outside here so these are

ther

cells and you still have your granulosa

cells and you still have your zone of

paluca

granua

cells this now is called a secondary

follicle

secondary

follicle and this secondary follicle

will turn into now I haven't told you

about what they do I will I promise I'm

just going through the phases the

secondary follicle will turn into a

mature ultimately a mature follicle now

what this mature follicle does by day 14

is it ovulates now what that means is

that you have these granular cells like

this you have these F cells that have

now developed even further right on the

outside and the uite

has ovulated and it takes some cells

with it because it still needs to be

nourished right now that's an important

point because I haven't told you what

any of these cells do as it goes from

Day Z to day 14 the development of this

follicle these follicles which we call

the follicular phase from a primordial

follicle to a primary follicle to a

secondary follicle to what we call a

mature or graffian so let's call this an

anol or let's call it a

graphion or you could even call it a

mature follicle

right this is the one that ovulates now

the granulosa cells and the Thea cells

are super important what the granulosa

and ther cells do is they ultimately

produce estrogen now specifically one

type of estrogen that's most important

here is called estral now here's the

thing this whole process

going from here to around about here is

independent of any hormones it really

doesn't need hormones to do this right

now if we have a look down and look at

the hormones what's happening during

this process let's first focus on

luteinizing hormone and follicle

stimulating hormone now remember these

hormones these two here they're

ultimately

released from the

hypothalmus right specifically they're

released from the anterior pituitary

gland so what happens is the

hypothalmus the

hypo thelus will release a hormone

called gonadotropin releasing hormone

and this goes down to the anterior

aspect of the pituitary

gland which then

releases these hormones this happens at

puberty right now let's have a look at

what's happening at these hormones

lutenizing hormone and follicle

stimulating hormone they're not super

high right let's start with ltin let's

start with uh follicle stimulating

hormone so what you'll find here is that

follicle stimulating hormone at Day Zero

is up

here and it starts to drop down right

let's do the same with lutenizing

hormone right lutenizing hormone it's

here and it starts

to drop down slowly interesting now

importantly what these two hormones do

most specifically follicle stimulating

hormone is by the time we hit this phase

here we need follicle stimulating

hormone to

stimulate these secondary follicles to

turn into more mature follicles to these

anal follicles graphium follicles more

mature follicles we need FSH for this if

FSH isn't here at this step what ends up

happening is these cells just all die

off now every month right at Day Zero

you have around about 10 to 30 of these

these follicles undergoing this process

and again without FSH they'll all just

undergo a treesia and die so what you'll

find is that because FSH is released it

allows for that selection process now

here's the other thing that's important

as it selects and it's going to take

from 10 to 30 it's only going to select

one right one mature one to ovulate one

single ovam as it does this and these

granulosa and ther cells get bigger and

bigger and bigger these granulosa and

Thea cells produce estrogen so as the as

the follicle develops the estrogen right

estral specifically it starts low but it

starts to

go

higher now can you see a pattern here

right as the estrogen gets higher the

FSH and LH gets lower this is important

because the estrogen that's released

from these Thea and granulosa cells goes

back to the

hypothalmus and says and provides

negative feedback says stop releasing G

outat trop and releasing hormone stop

releasing luteinizing hormone and

follicle stimulating hormone why would

it want to do that it does that because

it's now already selected its one mature

follicle that it wants so there's no

point continually releasing these

hormones to keep this process happening

we want it these to stop and just have

that one selected one now the estrogen

will continue to go up and inhibit the

FSH and LH until something important

happens right so again we're not at day

14 yet we're not at this point what

we're going to find is as we get just

maybe like 24 hours before day 14 the

estrogen levels that are released by

these ther and granulosis cells it's

starts to just Spike right up now here's

the interesting thing while relatively

low levels of estrogen inhibit FSH and

LH high levels of estrogen stimulate

them we don't know why but it does and

so when we have this higher level of

estrogen and it stimulates FSH and LH

what we end up

getting is the FSH down here and the LH

down here but once it starts to get

right once these levels start to get

high enough we get a surge now the surge

in this case predominately is going to

be that

of lutenizing hormone we also get a

surge of

FSH but importantly we've got this big

surge of LH and again this big surge of

LH is happening just before day4 and

what this big surge of LH does is FSH

follicle stimulating hormone is really

important in the follicular phase that

makes sense right so FSH is really

important in this phase

here at day 14 where we have ovulation

let's write that down I think that's

important day 14 where we have ovulation

occurring this is

important because of

LH LH is responsible for that ovulation

beautiful so that's because of that

Spike there now the thing is that once

this

happens we've got the ovulation

occurring the egg has been taken up by

the fim and is now in the uterine tube

right the fallopian tube let's just have

a look here right this remaining thing

here if I were to draw it

across we're now in the luteal phase

right so we've now got this

big empty looking body

and this big empty looking body starts

to produce a whole bunch of

progesterone this is called the corpus

luteum hence why it's called the luteal

phase so this is called the Corpus

Corpus means body right

luteum luteal means yellow it looks

yellow right because

cholesterol we turn

cholesterol

into

progesterone and we turn

progesterone into androgens right like

testosterone and we turn

androgens into

estrogen like

estradiol all comes from cholesterol so

what's happening in this corpus luteum

phase that goes throughout this process

here is it starts to produce huge

amounts of progesterone so what we end

up getting is low levels of progesterone

through most of this process we have a

little bit of a spike here but once we

hit day 14 and this corpus luteum

happens we get this big

spike of progesterone right we get this

big spike of progesterone what happens

with all these other ones they start to

drop off again so we got estrogen

dropping off we've got follicle

stimulating hormone dropping

off and we've got oh sorry luteinizing

hormone dropping off and we've got

follicle stimulating hormone dropping

off but here for this luteal phase we've

got heaps of progesterone all right we

haven't spoken at all about what's

happening in the endometrium so

far the endometrial lining or the

endometrium or the uterus has three

major phases the first phase is called

menes and this is

bleeding now as you can see menes goes

to round about day

five day five and then after bleeding

after menes we've got the proliferative

phase we've got the proliferative

phase

proliferative and then we've got the

secretory

phase now remember this this is what's

happening at the endometrium the

secretory phase so if we look at

endometrial changes that occur so just

so we've got enough room I'm going to

drop these because I didn't do units

it's okay I'm just looking at gross

changes that happen so that's not a

problem I didn't do any units on purpose

and it's important to understand the

unit changes here because some are

measured in

microliters uh micrograms per microl or

mil some are measured in pics nanog so

they're all you can't compare them in

regards to their concentrations this is

just general uh spikes for example and

Peaks and troughs now the endometrium

what happens menes menes is bleeding

goes for about 5 days if we have a look

at the thickness of the uterus it like

this it's going to be thick and then it

starts to bleed away and Slough off so

if this whole thing was the what we call

the functional layer of the uter of the

endometrial lining we're focusing on the

functional layer the functional layer is

the layer that can implant the

fertilized embryo but also can thicken

become more vascularized and produce

enzymes and uh various secretions like

mucus during menes the uterine lining

gets thinner and that's because bleeding

is occurring it's sloughing off this

sloughing off is happening because the

hormone levels are really low that's

important but as you can see in the

proliferative phase it starts to get

thicker again now it's getting thicker

again because we're starting to get an

increase in estrogen levels what

estrogen does is it increases the

thickness of the endometrium right so it

starts to get thicker that's great as

you can see as we move through and not

just uh estrogen is being produced we

now start getting progesterone

progesterone reinforces this and says

hey endometrium get thicker get more

vascularized and by the so here we got

the proliferative phase this is simply

just saying get thicker get thicker get

thicker get thicker right then the

secretory phase is saying now start to

develop glands start to develop glands

and this is in big part due to

Progesterone that we can now produce

enzymes that we can now produce mucus

and so forth and then what we end up

getting is once these hormones like

progesterone start to drop back down

again towards 28 days and once estrogens

drop back down again and then once

follicle stimulating hormone lutenizing

hormone have dropped back down

again the hormones are low again at the

end of day 28 and like I said the low

hormones is what causes the sloughing so

towards the end of day 28 we start to

get that drop down again so we've got

Menses which is bleeding that's

happening at this stage proliferation

this is all right so let's think about

it like this right follicular phase is

very much so due to FSH luteal phase is

very much due to

LH like I said FSH helps to produce

estrogen right so the proliferative

phase is really important uh when it

comes uh estrogen is really important

when it comes to the proliferative phase

the secretory phase luteinizing hormone

which produces ovul ovulation of Corpus

Lum and ultimately produces heaps of

progesterone is very much so due to

Progesterone

now this there's a huge amount of

overlap obviously because LH is

important here and FSH is important here

progesterone is important here and

estrogen's important here but broadly

generally speaking these are the

important hormones involved mostly in

these Cycles or this uh these phases of

the Cycles so importantly day 14

ovulation right day 28 hormone levels go

low again from Day Zero they start to go

back up estrogen is inversely

proportional to the FSH and LH so

they're going outat tropin until the

estrogen levels get quite High then they

both Spike that spiking of the LH maybe

24 hours before day 14 is what

stimulates ultimately ovulation to occur

the LH helps stimulate the Corpus Lam to

produce progesterone and this

progesterone as you can see will last

around about 10 days right so the this

progesterone is really important lasts

around about 10 days

is and then drops back down down why

well this Corpus Lum will release the

progesterone for round about the 10 days

and what it's doing is it's basically

said it's basically said to the egg that

it's ovulated remember where's this egg

now this egg has gone into the fim and

has been taken in and is in the uterine

tube and it's in the ampul and hopefully

fertilization occurs if fertilization by

sperm occurs that egg which then starts

to grow and divide as it moves through

the uterine tube can hopefully implant

in this nice thick endometrium that's

developed right in this window is here

so this is we've got this important

window here where it needs to implant if

it and so we've got this progesterone

being released to keep the endometrium

nice and thick for that implantation

window but if there's no sperm and

there's no fertilization there's no

implantation what ends up happening is

that once it does if it does get

fertiliz and implanted it starts to

produce a hormone called human chonic

gonadotropin so if it does implant right

if it does implant and start to divide

and so forth it will release

human

chonic gadat

tropen basically it pretends to be gadat

tropen and it is like a phone call back

to the Corpus lium saying hey

everything's good I'm here keep

producing progesterone so if that does

get implanted that doesn't stop at 28

days it keeps going that means if it

keeps going it stays thick so that the

embryo can develop and you don't get

Menses you don't get bleeding but if

there's no implantation there's no human

caronic Gat tropin there's no phone call

back after 10 days it stops producing

progesterone and the tissue starts to

diminish and sloughs Away you get

bleeding that's mens's the whole cycle

starts again so I hope that this helps

and this makes

sense hi everyone Dr Mike here if you

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