New Year!

Happy New Year to all!

At this time every year, without fail, there arises a new hope and inspiration to make this year better than the last. People make new resolutions, have new dreams and hope for a better tomorrow. Of course, I'm included in "people," and yes, I have made a list (a short one) of new resolutions I can only hope to keep for the whole year. No, I will not make them public, but I have written them out and kept them in a spot that I will be constantly reminded! One of the common themes that I've seen in the resolutions of many peeps is "being healthier." So simple, yet so DIFFICULT-being healthy could include working out more, or eating more veggies, or simply cutting down on eating out at restaurants. Well, in order to be a bit more healthy, why not start by understanding how the body works!  You've come to the right place folks (haha, I feel like I tricked you all into reading about health after all this talk about the new year).

Since I've just finished Ob/Gyn, I figured I should provide some basic information about women's health. Guys..sorry in advance-but read on to learn a bit more about your girlfriend/wife. Today, we'll talk about the menstrual cycle. Let's get started! I know many have learned this in health class or various other sources but its a bit more complicated than how it was first presented to me! So here goes...

PERIOD-is not the end, but the beginning!

In short, the menstrual cycle is a series of bodily events that occur in preparation for pregnancy every month starting at puberty. It usually is about 28 days long (the length varies for each woman), and involves several different organ systems. Scroll down to see the summary picture. The basic picture is that hormones released from parts of the brain (hypothalamus & pituitary) act as signals to control events occuring in the ovary -- which will also produce its own hormones that lay their effect on the lining of the uterus. Let's break it down day by day and get to know that happens in the body.

• Days 1-5: Early Follicular/Menses-technically the start of the cycle, however its significance is that the last menstrual cycle has ended and pregnancy was not achieved. 
• BRAIN: During menses, due to lack of fertilization, estrogen and progesterone levels are low, and lack of negative feedback causes the hypothalamus secretes GnRH (gonadotrophin releasing hormone) in pulses to stimulate the pituitary gland to release FSH (follicle stimulating hormone) and LH (luteinizing hormone). 
• OVARY: FSH levels begin to rise and make their way to the ovary to stimulates and recruit "premature" follicles (aka primordial follicles).
• LH doesn't have much of a role during the menstrual cycle because its secreted in tiny amounts-it'll be much more crucial later on. 
• UTERUS:  the body "starts over" by shedding the lining of the uterus (endometrium) that is built up all month to provide a nurturing environment for the fetus. This too, is in response to the fall in hormonal levels [estrogen and progesterone-released by the remnant of ovarian follicle that the egg resides in ] that help sustain the endometrial lining. 
• Days 6-10: Mid-Follicular/Proliferative phase. This phase is mostly characterized by the growth of follicles in the ovary. 
• BRAIN: continued secretion of low levels of FSH from the pituitary. 
• OVARY: When the ovary receives FSH signals, several follicles (immature eggs) begin to grow and mature (with a hope that one of them gets fertilized this time around), and ultimately one follicle is selected
• As the follicle matures, one of its cells separates and becomes the egg, whereas the others form two layers - theca interna and externa. The theca interna begins to secrete estrogen. 
• The estrogen released by the maturing follicle serves as a signal to the uterus-causing it to start the proliferation of the endometrial cells in preparation for conception.
• The increase in estrogen relays back to the brain and had a negative feedback effect causing a decrease in serum FSH and LH levels. 
• The increase in estrogen also causes proliferation of the glands in the endometrium of the uterus in preparation for conception. This can be seen in by the ultrasound as a "triple stripe" shown below: 

• Picture courtesy of: AdvancedFertility
• Days 11-15: Late Follicular/Proliferative phase: 
• BRAIN: During this phase, LH becomes very crucial in the menstrual cycle. We see that FSH and LH are secreted at low levels still due to negative feedback from estrogen. 
• OVARY: The dominant follicle is now selected and continues to grow whereas the other growing follicles stop and degenerate. The estrogen (from the maturing follicle) continues to increase - keeping the proliferation of the  endometrial lining going. Estrogen levels rise and peak one day prior to ovulation. 
• UTERUS: The endometrial lining also gradually thickens and the cervical mucus becomes stringy (a test that can be used to monitor ovulation). 
• Days 15-16: Ovulation: The release of the egg from the maturing follicle. 
• BRAIN: As the estrogen peaks a day before ovulation, it results in a mid-cycle surge  of LH due to a switch in negative feedback control into a positive feedback of estrogen on LH receptors in the hypothalamus. 
• OVARY: The sudden spike of LH causes the dominant follicle to undergo its first division of meiosis. The granulosa cells surrounding the oocyte in the follicle begin to luteinize just prior to its release and start releasing progesterone. Soon, the oocyte (egg) is released from the follicle and it is then free to travel down the fallopian tube into the uterine cavity. 
• UTERUS: Progesterone concentrations increase and stops the proliferation of the glands. The triple stripe (shown below) is lost and the uterine lining becomes brighter and more uniform. 
• Days 16-28: Luteal phase/Secretory phase
• BRAIN: A gradual decrease in LH is seen soon after ovulation and taper off.
• OVARY: estrogen and progesterone is continued to be secreted by the corpus luteum (remnant of the follicle) and rises up until the middle of this phase. 
• IF NO FERTILIZATION OCCURS: Estrogen and progesterone production will eventually drop due to the regression of the corpus luteum in absence of a fertilized oocyte. 
• IF FERTILIZATION DOES OCCUR: The fertilized egg begins to produce another hormone called human chorionic gonadotropin (hCG) that maintains the corpus luteum, and therefore estrogen and progesterone levels will remain elevated to support the pregnancy. 
• UTERUS: The uterus lining is maintained up until the estrogen and progesterone start to decline if fertilization does not occur. When the levels become very low, the endometrium loses its blood supply and starts to shed, marking the onset of menses and the beginning of a new cycle. This occurs 14 days after the LH surge.

Phew...now that was a lot to learn!  Check out the figure below to make sense of what goes on: 

Picture courtesy of: Eurocytology

So now we have some basis of the monthly happenings in a woman's body. In upcoming blogs, we'll be talking about what can go wrong with the cycle! Hope this helped clear up any confusion! 

Until next time :)