10: The Menstrual Cycle Physio Flashcards
Describe the basis of the menstrual cycle
Out menstrual cycle describes the changes to our ovarian follicles and endometrium that occur post-pubert in F. It lasts 28 days; from 1 period -> next. It made up of 2 phases:
- Ovarian cylcle
- Endometrial cycle
Ovulation (release of a. mature. egg) occurs at mid-menstrual cycle (day 14).
Pre-ovulatory period (days 1-14)
- Ovarian cycle: follicular phase. (maturion of follicle and oocyte)
- Endometrial cycle: (menstrual phase and proliferative phase)
Post ovulatory. period (days 14-28)
- Ovarian cycle: luteal phase (what occurs with remant of follicle and oocyte)
- Endometrial cycle: secretory phase.
Puberty marks the transition to a cyclic, adult reproductive function.
Girls undergo thelarche, adrenarche and menarche during puberty.
Describe that these words mean.
- Thelarche -> breast develpoment
- Adrenarche -> increase in adrenal androgen secretions
- Menarche -> beginging of period.
How do levels of gonadotropins change through life of a female?
- B4 puberty, GnRH is released steadily at LOW levels.
- At puberty, we begin to see oscillartory pulses of gonadotropin being released in REM sleep.
- After puberty and in reproductive years (after 14), it is released in pulses at day and night, causing small surges of FSH release and large surges of LH release
- Sensoscence: Decreased levels of estrogen cause high levels of FSH/LH (higher FSH) secretion d/t menopause. We will see highest levels of steadily released FSH and LH.
The ovary can be divided into what?
Outer cortex and inner medulla, where neurovascular elements run though.
What makes up the CTX of the ovary?
- Dense cellular stroma surrounded b simply epithelium.
- Ovarian follicles are located in the stroma and contain a primary oocyte.
The process of _________ involves inflammatory events that e_rode the wall of the ovary and follicle._
Ovulation
What is the functional unit of the ovary?
Ovarian follicle
What is the ovarian cycle?
Ovarian cycle has 2 phases:
-
Follicular phase
* Days 1-14, leading up to ovulation on day 14
* Coincides with proliferative phase of endometrium cycle)- maturation of the ovarian follicle, competing to grow the fastest so one can be ovulated.
-
Follicular phase
-
Luteal phase
* The following 14 days after ovulation
* Coincides with secretory phase of endometrial cycle).
-
Luteal phase
What is the endometrial cycle?
3 phases:
- Menses (menstrual phase)
- Proliferative phase
- Secretory phase
LETS START WITH OVARIAN CYCLE
LETS START WITH OVARIAN CYCLE
LETS START WITH OVARIAN CYCLE
LETS START WITH OVARIAN CYCLE
Follicle goes through what stages?
- Resting primordial follicles
- Growing preantral follicles
- Growin antral follicles
- Dominant (preovulatory, graafian) follicle
- Dominant follicle within the periovulatory period
- Corpus luteum (of menstruation or pregnancy)
- Atretic follicles (degenerate before coming mature)
Oocyte maturation produces what?
Follicles mature from primordial -> graafian (preovulatory) follicles to create a
Haploid female gamete that can be fertilized be a sperm, begining in the female ovary.
_________ is the earliest and simplest follicular structure in the ovary.
Describe this cell.
Primordial follicle
1 layer pregranulosa cells
Releases paracrine factors, but not hormones.
4N DNA
First primordial follicle usually appears_____ into intrauterine life;
generation of primordial follicles is done by _____months after birth
6 weeks
5-6. months
__________ restrains the development of too many primordial follicles
AMH
Do all of our primordial follicles (4N DNA) enter follcular growth?
No. Primordial follicles are our primordial reserve, which most will be lost d/t atresia. Only a small subset (400-500) grow).
The rate at which _______________ die/develop determines reproductive lifespan of a woman.
resting primordial cells.
What gamete is located inside primordial follicles?
- Primary oocytes arrested in the 1st meiotic prophase and can remain for 50 years.
Primordial follicles develop into what?
Growing preantral follicles
- Primary follicle (4N DNA): primary oocyte surrounded by single layer of granulosa cells that begin to secrete fluid and zona pellucida begins to develop.
-
Secondary follicle (4N DNA): primary oocyte surrounded by 3-6 layers of granulosa cells. Once this happens, paracrine factors are secreted and cause stromal cells -> thecal cells.
* Zona pellucida develops even more to provide binding site for sperm.
When can we refer to a secondary follicle as a mature preantral follicle?
Once thecal layer forms.
The progression to secondary follicles involves what?
-
Increased vascularization;
- follicle moves from outer CTX -> inner CTX, closer to vascularizatture of ovarian medulla.
- They will then release angiogenic factors that make arterioles, which. make a. sheath. around the follicle.
What happens to the gamete in the. growing preantral follicle
- Oocytes are arrested. is meisosis. I. prophase.
- Oocyte begsin to grow and make/secrete proteins, such as ZP1, ZP2, and ZP3 that will make the. zona pellucida, which makes a. binding site for sperm.
- Granulosa cells and oocytes have extensions through. the zona. pellucida and maintain. junctional contacts ,allowing for communication. and nutrition
*
What is the endocrine functions of the growing preantral follicles?
They have LITTLE endocrine function.
Granulosa cells. will have FSH receptors, but depemnd on paracrine factors from oocyte to grow. They will not make hormones at this point.
What are thecal cells analogous to in males?
What do they do during the growing pre-antral follicles?
- Leydig cells.
- Thecal cells have LH receptors and make androstenedione.
- In growing preantral follicles, thecal cells make LITTLE/none androstenedione.
The development of an antrum depens on what?
antrum- > fluid containing steroid hormones, mucopolysaccharides, proteins and FSH in a follicle
GONADOTROPINS!
Early antral follicles depend on FSH to grow normally. As they get larger they will become HIGHLY dependent for growth and viability.
We have now become a early antral follicle.
In the growing antral follicles, what happens to the granulosa cells?
- Increase in number and we get 2 populations
-
Mural granulosa cells become v steriodogenic.
- After ovulation, they stay in the ovary & become corpus luteum
-
Cumulus cells (cumulus oophorous/corona radiata) maintain gap and adhesion junctions with the oocyte.
- At ovulation, they are released with oocyte.
-
Mural granulosa cells become v steriodogenic.
What happens to the gamete in antral follicles?
- Oocyte grows rapidly at first but slows down in larger follicles.
- Oocyte becomes competent. to completes meoisis I at ovulation.
- Larger antral follicles gain meiotitic competence, but are still under arrest d/t elevated cAMP until the LH surge occurs.
Growth during the antral stage becomes responsive to what?
GONADOTROPINS!
Theca cells develop LH receptors and bind LH -> [cholesterol and acetate-> androstenedione and testosterone]
Mural granulosa cells develop FSH receptors and bind FSH -> secrete aromatase
- Aromatose converts androstenedione into 17B-estradiol.
- Will also secrete inhibin in the early follicular phase.
How do we determine our DOMINANT follicle, the one that will undergo ovulation?
Follicles grow, as estrogen is being released into bloodstream
- Increase estrogen levels feedback and tells AP to secrete less FSH and LH.
- D/t decrease FSH, some follicles will undergo atresia
However, in the early follicular phase, follicle with most FSH receptors (most responsive) will continue to grow and become DOMINANT FOLLICLE that will undergo ovulation.