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Flashcards in Periods 101 Deck (18):

Menstrual cycle is a ...

Menstrual cycle is a reflection of cyclic release of hormones on the hypothalamic-pituitary-ovarian axis (HPO axis).


The hypothalamus pituitary ovarian axis releases hormones…

GnRH is secreted by the hypothalamus which stimulates cells anterior pituitary to make FSH and LH which act on the ovaries.


GnRH stands for

Gonadotropin releasing hormone is secreted in pulses by the hypothalamus and starts the menstrual cycle.


FSH stands for ...

Follicle stimulating hormone

FSH stimulates follicles so that they grow and produce estrogen.
Link: FSH, follicles, estrogen


LH stands for ...

Luteinizing hormone, promotes ovulation

Link: ovulation


Menstrual cycle consists of ..

The ovarian and uterine cycle, which each have three phases.


Ovarian cycle, three phases ...

Follicular phase
Ovulatory phase
Luteal phase


Uterine phases ...

Proliferation phase
Secretory phase
Menstrual phase


Ovarian cycle, follicular phase, details ...

Follicular phase
- starts on day 1, start of menses, and ends just before ovulation
- 10 - 17 days (variable), most variable phase
- estrogen rises during days 1-5
- mid-follicular phase ... Competition to become dominant follicle


Follicles are ...

Follicles are little fluid filled sacks with an immature egg in the middle. About 1 million follicles exist at time of birth, many are absorbed during childhood. By puberty about 400,000 left that are eligible to develop into eggs.

During the first half of the follicular phase, 10 to 20 follicles are recruited to start growing. These follicles are estrogen factories. The 10 - 20 recruited follicles compete against one another to become the dominant follicle.

Dominant follicle selection happens on day 7.


Recruited follicles are ...

Estrogen factories


Follicular phase, estrogen ...

From day 1 to 7, estrogen levels increase but remain moderate which inhibits the secretion of FSH and LH by the anterior pituitary. This is a classic negative feedback loop.

Day 7, the dominant follicle is established, the other follicles break down through a process called atresia.

Day 7 to the end of the follicular phase, the dominant follicle continues to mature and produce high levels of estrogen. The high levels of estrogen stimulates FSH and LH in the classic positive feedback loop leading to the ovulation-inducing LH surge.

At the end of the follicular phase, the mature follicle bulges on the surface of the ovary ...


Ovarian cycle, ovulatory phase

Ovulatory phase:
- LH surge, then ... 32-34 hours post surge start, 10-12 hours post peak
- Follicle protrusion, vesicles rupture, oocyte expulsion
- Ovulation


Ovarian cycle, Luteal Phase

Luteal phase ...
- begins with ovulation and ends with menses
- last 14 days, with little variety, highly reliable
- post ovulation, walls of follicle collapse,
- dominant follicle becomes corpus luteum (CL) "yellow body"


Ovarian cycle, Luteal phase and ____ hormone ...

Luteal phase:
- the corpus luteum (CL) produces large amounts of progesterone.
- this progesterone suppresses the growth of new follicles
- progesterone causes an elevation in basal body temperature
- if no conception, 9-11 days post ovulation, CL regresses rapidly
- CL regression results in decreasing progesterone levels
- withdrawal of hormones ... Menstruation


Uterine cycle, proliferative phase ...

Proliferative phase, cycle days 5 - 14:
- increasing plasma estrogen levels
- proliferation of endometrial glands and stromatolites
- endometrium thickens and regenerates
- Cervical changes: endocervical glands, stimulated by estrogen, produce thin, clear mucus to lubricate vagina, facilitate sperm capture, and transport

ESTROGEN dominant phase
Changes that help a woman become pregnant.


Uterine cycle, secretory phase ...

Secretory phase, cycle days 14 - 28:
- progestational phase ... Progesterone acts on estrogen-primed endometrium
- endometrium thickens and secretes glycogen, mucus, and other substances
- progesterone encourages uterine quiescence, prevent expulsion of ovum, conceptus
- cervical mucus thick and sticky

PROGESTERONE (d/t CL) dominant phase
Changes that help a woman to stay pregnant


Uterine cycle, menstrual phase ...

Menstrual phase, days 1 - 5:
- degeneration of endometrial lining
- sloughing = menstrual flow
- constriction of spiral arterioles ... Decreased blood flow and oxygenation to endometrium