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Please make sure to 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 but hopefully we’ll be able to understand it by the end of this video, so
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 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 fsh, follicle stimulating hormone and lh luteinizing hormone please note that in males this same process also occurs males also produce 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 which connects to the uterus via the fallopian tube essentially but it’s now known as a uterine tube so we focus on this over here, so let’s zoom in this and it’s through these capillaries these blood vessels that the hormones can enter 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 the hormone concentrations here we have a y-axis which shows the concentration of the hormones in blood and on the 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 is known as the luteal phase and this is important to keep in mind, so the first is the follicular phase now initially in
The beginning of the menstrual cycle there is an increase in gonadotropin releasing hormone secreted by the hypothalamus this should cause a steady increase in follicles stimulating hormone and dropping level of follicle stimulating hormone, and we have a steady level of luteinizing hormone well the reason is actually quite complicated, but just hold on to that thought
And hopefully it’ll make sense 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 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 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 from the
Hypothalamus is stimulating the release of luteinizing hormone at another fact is that follicle stimulating hormone is secreted 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 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 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 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 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 the increase in gonadotropin releasing hormone and estrogen will stimulate and you see this massive spike in luteinizing hormone concentration
Luteinizing hormone concentration that will trigger the ovulation of the follicle will release what we know as the female egg the 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
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 is called the follicular phase because it all has do with the follicles and its maturation and the last 14 days is known as the luteal phase however it also has a purpose it in that it secretes hormones. it secretes three
Hormones estrogen again so what we see in the concentration levels of these ovarian hormones 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 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 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 the luteal phase and has many functions of which is having a negative effect on the hypothalamus inhibiting the secretion of gonadotropin releasing hormone the progesterone levels will increase slowly and the estrogen levels will decrease slowly kind of and this will
Suppress gonadotropin releasing hormone release so progesterone will inhibit gonadotropin releasing hormone release which will also the release of luteinizing hormone and follicle follicular stimulating hormone? so during the luteal phase as progesterone and inhibin increase 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 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 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 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 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
Transcribed from video
Female Reproductive System – Menstrual Cycle, Hormones and Regulation By Armando Hasudungan