Facts on Menstrual cycle

When I was still a student, I didn’t like maternal and child nursing or topics that pertain to taking care of pregnant women and the child. I really find it hard to understand and memorize facts about it and so I really am having difficulty appreciating it. But then again, when you are in this profession or whatever profession you are in right now you really could not get away from topics that you hated most back when you were studying. And so, I would like to take this opportunity to share to you some information’s from Maternal and child nursing which I think is very helpful not only for me but also for all of the students out there who are finding their way to becoming a nurse. Lets start from some basic concepts.

Menstrual Cycle Physiology

What is the average duration of the                              The average duration of the

menstrual cycle, duration of menses, and                  menstrual cycle is 28 days. The

amount of blood loss during menses?                         average duration of menstrual flow

is 4 days. On an average, women lose

less than 60 mL of blood during each

menses

What are the two phases of the menstrual                 Follicular (or proliferative) phase and

cycle and how long does each last?                             the luteal (or secretory) phase,

separated by ovulation. (Follicular/

luteal describe the ovarian changes,

proliferative/secretory describe the

endometrial changes)

By convention, day 1 marks the onset

of menses. The follicular phase begins

on day 1 and lasts approximately

14 days (days 1–14) in a 28-day cycle,

until ovulation occurs. The luteal

phase then commences and lasts until

approximately day 28 (days 14–28)

What causes the variability in the length                     The duration of the follicular phase

of the menstrual cycle?                                                    (the luteal phase is constant)

Describe the hormone pathway involved                    The cycle begins in the arcuate

in the menstrual cycle (see Fig. 4-1) and                     nucleus of the hypothalamus where

name which structures produce                                   gonadotrophin-releasing hormone

each hormone                                                                     (GnRH) is released in a pulsatile

fashion. GnRH stilmulates the

anterior pituitary to release folliclestimulating

hormone (FSH) and

luteinizing hormone (LH). These

gonadotropins then cause the ovaries

to release the sex steroid hormones

estradiol and progesterone.

Estrogenand progesterone feedback

negatively on both the hypothalamus

andthe pituitary gland

What is happening in the ovary during the                     The ovary beings with

menstrual cycle?                                                               approximately one million primordial

follicles at birth (20 million at week

20 in utero). Each follicle contains an

oocyte arrested in prophase of

meiosis. The oocyte is surrounded by

pre-granulosa cells and these are

surrounded by pre-theca cells. In the

follicular phase, FSH stimulates the

pre-granulosa cells to become

granulosa cells. The granulosa cells

secrete estradiol. The pre-theca cells

in turn become theca cells and secrete

androgens, which are aromatized by

the granulosa cells into estradiol.

One follicle with the highest number

of granulosa cells, FSH receptors, and

estradiol production becomes the

dominant follicle and all other

follicles become atretic. This follicle is

released during ovulation and

becomes the corpus luteum. The

corpus luteum secretes progesterone

and a smaller amount of estrogen

during the follicular phase of the

cycle. If fertilization does not occur, it

degenerates into the corpus albicans

What is the function of the corpus luteum?                Secretion of progesterone and

estradiol. It is the only structure that

produces progesterone in significant

quantities which sustains the

pregnancy until the placenta is

developed

What is happening to hormone levels in                      At menstruation, concentrations of

the follicular phase?                                                          estradiol, progesterone, and LH are

at their lowest point. FSH and LH

levels begin to rise in response to

the low estrogen and progesterone.

Estradiol levels, secreted from the

dominant ovarian follicle, begin to

rise by day 4. Just before ovulation,

estradiol levels peak. This peak

causes a positive feedback on LH

secretion, leading to the LH surge

and a smaller FSH surge, which

results in ovulation 30–38 hours

later. Progesterone levels remain low

throughout the follicular phase

 

What is happening to hormone levels in                      The LH surge causes granulosa and

the luteal phase?                                                                theca cells to secrete progesterone

and smaller amounts of estrogen.

Progesterone peaks 3–4 days after

ovulation.

Estrogen levels decrease immediately

after ovulation but slowly rise with

the growth of the corpus luteum.

Progesterone and estrogen (at low to

moderate levels) both act via negative

feedback to suppress LH and FSH. If

fertilization and implantation do not

occur, progesterone and estradiol

levels diminish after 11 days. FSH

increases as the corpus luteum

regresses

What is happening to the endometrium in                   At menses, the endometrium sloughs

the proliferative phase?                                                   off until it becomes a thin line. During

the proliferative phase estradiol levels

rise, resulting in the proliferation of

the uterine endometrium. The

endometrium becomes thicker and

more glandular and the spiral arteries

elongate. On ultrasound, it appears as

a “triple stripe” pattern

What is happening to the endometrium in                   The progesterone released from the

the secretory phase?                                                        corpus luteum leads to slowing of

endometrial proliferation,

reorganization of the glands (resulting

in a more edematous stroma), and

further coiling of the spiral arteries.

This results in the loss of the “triple

stripe” pattern and its replacement

with a uniformly bright

endometrium. If pregnancy does not

occur, the endometrium degenerates

What are the primary clinical                                          Estradiol

manifestations of estradiol and                                     Endometrium: thickens stroma and

progesterone during the menstrual cycle? elongates glands (creates proliferative

endometrium); Endocervix: stimulates

secretion of thin, watery mucus.

Produces “ferning” pattern when

spread on a glass slide;

Vagina: promotes vaginal thickening

Progesterone

Endometrium: causes tissue to

become edematous and blood vessels

to thicken and twist (creates

secretory endometrium);

Endocervix: thickens endocervical

mucus, causing it to become stringy;

Breast: stimulates acinar glands,

causing breasts to round;

Other: raises basal body temperature

by 0.6–1°F. Causes some women to

have the emotional, physical, and

behavioral changes of premenstrual

syndrome (PMS)

What layer of the endometrium sloughs                      The functionalis layer (inner layer)

off during menses?                                                           sloughs off after glandular and

stromal degeneration

What hormone mediates menstrual                             Prostaglandins, especially PGF2á. It is

cramps and how is it synthesized?                               released by the secretory

endometrium in response to

progesterone and causes uterine

contractions

That’s it. Hope you learned something from this. Next time, I will be posting about family planning.. till next time..