Women's Health : The Menstrual Cycle Flashcards
The menstrual cycle begins with _____ follicles
15-20
Which type of follicle undergoes ovulation?
Graafian follicle
What are the 5 components of a follicle?
- A primary oocyte 2. A zona pellucida - a protein coat surrounding the oocyte 3. Granulosa cells - these express FSH receptors, which stimulates them to convert androgens produced by theca cells into oestradiol. 4. A fluid-filled antrum. 5. Theca cells - these express LH receptors, and produce androgens.
What is the zona pellucida?
Protein coat of oocyte- a protein coat surrounding the oocyte
What do granulosa cells express?
FSH receptors
What do FSH receptors stimulate?
stimulates them to convert androgens produced by theca cells into oestradiol.
What is the role of granulosa cells?
Convert androgens to oestradiol
What type of receptor do theca cells express?
LH receptors
What do theca cells produce?
Androgens
What happens to granulosa cells after ovulation?
After ovulation, the granulosa cells of the ruptured Graafian follicle undergo luteinisation to become the progesterone-secreting corpus luteum - this has a 10 day lifespan before it begins atresia (continues secreting progesterone for 14 days).
What are the names of the phases of the menstrual cycle?
The menstrual cycle is therefore split into the follicular and luteal phases, separated by ovulation.
What does the corpus luteum secrete?
Progesterone
What is the lifespan of the corpus luteum?
10 days
How long does the corpus luteum continue to secrete progesterone?
14 days
What dictates the menstrual cycle?
hypothalamic-pituitary-gonadal (HPG) axis.
Where is Gonadotrophin-releasing hormone (GnRH) released from?
Hypothalamus
GnRH travels from ______ to _____ via ______________
GnRH Travels from hypothalamus to anterior pituitary via hypophyseal portal vessel system
What is the secretion pattern of GnRH?
Secreted in a pulsatile manner at varying frequencies i.e. higher frequency, lower amplitude in follicular phase, and lower frequency, higher amplitude in luteal phase.
GnRH stimulates the secretion of ___ and ____
LH and FSH
GnRH is inhibited by ___ and ___ (negative feedback)
LH and FSH
Luteinising hormone (LH) and follicle-stimulating hormone (FSH) are released from?
Anterior Pituitary
LH and FSH are _____ hormones, collectively known as the _______ (and are produced by cells called _______)
Peptide hormones, collectively known as the gonadotrophins (and are produced by cells called gonadotrophs).
LH acts on which cells?
Theca cells
What does LH cause?
LH causes theca cells to produce androgens
FSH acts on which cells?
Granulosa cells
What is the effect of FSH on granulosa cells?
Convert androgens to oestrogen
Where do oestrogen and progesterone come from?
Follicles in the ovary
What type of hormones are oestrogen and progesterone?
Steroid hormones
At moderate levels, oestrogen exerts _______ feedback upon LH secretion
negative
At high levels, oestrogen exerts ____ feedback upon LH secretion
positive
When does oestrogen peak?
Mid-cycle
When does progesterone peak?
Day 21
Describe the levels of progesterone
progesterone is low throughout the follicular phase, but peaks 7 days before a menstrual bleed (i.e. day 21 of a 28 day cycle).
What feedback does progesterone exert?
Progesterone exerts negative feedback on GnRH secretion, reducing the frequency of its pulsatile secretion during the luteal phase.
What prepares the uterus for a fertilised oocyte?
Endometrium changes
What are the three layers of the endometrium?
The endometrium has three layers, which are also separated into two strata by their functionality in the menstrual cycle:Stratum functionalis, composed of the stratum spongiosum and stratum compactum
What are the two strata of the stratum functionalis?
Stratum spongiosum, Stratum compactum
The stratum functionalis proliferates under the influence of oestrogen in advance of ovulation - what are the 4 stages of this?
- Stratum spongiosum thickens through mitosis 2. Endometrial glands lengthen 3. Connective tissue stroma regenerates 4. Spiral arterioles lengthen
After ovulation, _______ acts upon the endometrium to cause it to secrete substances including ______ and _______ - this makes it more accommodating to a potentially fertilised oocyte
After ovulation, progesterone acts upon the endometrium to cause it to secrete substances including glycogen and mucous - this makes it more accommodating to a potentially fertilised oocyte
What happens if conception does not take place?
There is no beta-hCG to maintain the corpus luteum, leading it to spontaneously regress
With the withdrawal of its progesterone, the stratum functionalis degenerates and causes a menstrual bleed: Describe the 3 stages of this.
- Spiral arteriolar constriction causes tissue ischaemia. 2. Leukocyte infiltration into stratum functionalis takes place. 3. Spiral arterioles rupture
What does spiral arteriolar constriction cause?
Tissue ischaemia
What infiltrates the stratum functionalis?
Leukocytes
What ruptures leading to menstrual bleed?
Spiral arterioles
__________ release plays a significant role in inducing the menstrual bleed
Local Prostaglandin
What phase occurs during Days 1-14?
Follicular Phase, Menses and Proliferative Phase
Increased frequency of pulsatile GnRH secretion leads to an increase in __, and an initial increase in ___
Increased frequency of pulsatile GnRH secretion leads to an increase in LH, and an initial increase in FSH
How do oestrogen levels increase (days 1-14)?
Oestrogen rises gradually as granulosa cells convert thecal androgens under the influence of FSH.
Why do progesterone levels remain low (days 1-14)?
Progesterone levels remain low after loss of corpus luteum
What feedback do moderate oestrogen levels exert?
Negative on FSH
What occurs during Days 1-5?
Menstrual bleed
What causes the menstrual bleed?
Progesterone withdrawal due to degeneration of corpus luteum leads to sloughing of the stratum functionalis (a menstrual bleed).
What phase does the endometrium undergo from days 6-14?
Proliferative phase due to rising oestrogen levels
What happens during days 15-20
early antral (tertiary) follicles undergo development
What occurs on day 7 of the ovarian cycle?
a single dominant follicle is selected.( it is thought that this occurs because rising oestrogen levels lower FSH levels through negative feedback - the dominant follicle is the one that can cope with lower FSH.)
What happens on day 13 related to LH?
Rising oestrogen levels reach a ‘tipping point’, at which their negative feedback on LH secretion is reversed - the LH surge occurs, stimulating the oocyte to complete meiosis I and form a single Graafian follicle.
What triggers ovulation on day 14?
Antral fluid
What happens on Day 14?
Ovulation - The secondary oocyte erupts from its follicle, carried by antral fluid.
Days 15-28
Luteal phase and Secretory phase
What happens to granulosa cells on Day 15?
the granulosa cells of the ruptured follicle become luteinised, forming the progesterone-secreting corpus luteum.
What does the corpus luteum secrete?
Progesterone.
What phase does the endometrium enter due to progesterone?
The corpus luteum’s progesterone acts upon the endometrium to cause it to enter its secretory phase - amongst other things, it secretes glycogen and mucous.
When do progesterone levels peak?
7 days before the next menstrual bleed - 7 days before CL completely degenerates.
What do high levels of progesterone affect?
High levels of progesterone increase the volume and viscosity of cervical secretions; this begins the formation of the protective operculum.
What happens after 10 days if no conceptus implants?
the corpus luteum spontaneously regresses –> diminishing progesterone levels
What impact does low progesterone levels have on the endometrium?
Without progesterone’s negative feedback on the hypothalamus, GnRH release frequency increases and facilitates a rise in gonadotrophins. ○ Progesterone withdrawal also stimulates the stratum functionalis of the secretory endometrium to be shed
What causes the cycle to restart on Day 1?
As FSH and LH levels rise, and the menstrual bleed begins, the cycle restarts on Day 1.
How many oocytes does a developing female foetus synthesise in utero?
A developing female foetus synthesises upwards of 6 million oocytes while in utero.
How many oocytes remain by puberty, and what process reduces their number?
Approximately 300,000 oocytes remain by puberty due to a process called atresia.
What are the two broad categories of follicles?
Follicles are categorized as pre-antral and antral.
Which follicular phases are included in the antral category?
The antral phase includes primordial, primary, and secondary follicles.
What is a primordial follicle, and what does it consist of?
A single oocyte arrested in prophase I of meiosis. A layer of flattened (squamous) granulosa cells.
A basal lamina (extracellular matrix).
What happens to primordial follicles until puberty?
Until puberty, each oocyte remains part of a primordial follicle.
How do primordial follicles transition to primary follicles?
Through recruitment, where a portion of primordial follicles enters the menstrual cycle.
What changes occur in granulosa cells during the recruitment of primordial follicles to primary follicles?
Granulosa cells undergo mitosis.They change from a squamous to a cuboidal shape.
They start to express FSH receptors.
What does the oocyte synthesize during the recruitment to primary follicles?
The oocyte synthesizes mRNA to encode proteins that form the zona pellucida.
What are the components of a primary follicle?
A single oocyte.A surrounding zona pellucida.
A layer of cuboidal granulosa cells.
A basal lamina.
What transformations occur in the primary follicle to form a secondary follicle?
The granulosa cell layer thickens through mitosis. Theca cells form around the basal lamina.
A network of blood vessels develops in the outer follicle.
What is the tertiary follicle, and what happens at this stage?
The tertiary follicle, or early antral follicle, forms as a fluid-filled cavity (the antrum) develops within the granulosa cells.
What happens to one of the tertiary follicles during the follicular phase?
One follicle undergoes selection to become the dominant follicle at the midpoint of the follicular phase.
What event initiates the development of the dominant follicle into the Graafian follicle?
The LH surge initiates the development of the dominant follicle into the Graafian follicle.
What effect does the LH surge have on the oocyte?
It takes the oocyte out of its meiotic arrest. The oocyte completes meiosis I, forming the first polar body.
It proceeds to metaphase II, where it is arrested again.
What is a tertiary follicle with a complete antrum and a secondary oocyte called?
A Graafian follicle (an antral follicle).
What are the components of a Graafian follicle from deep to superficial?
A secondary oocyte (plus the first polar body).Zona pellucida.
Cumulus oophorus of granulosa cells, attached to further granulosa cells.
A fluid-filled antrum.
Basal lamina.
Theca cells (interna and externa).
What happens during ovulation?
The mature oocyte, along with its surrounding zona pellucida and cumulus oophorus of granulosa cells, hatches from the antrum.
What cells are attached to the surrounding cumulus oophorus?
Granulosa cells
What extracellular structure does the oocyte have surrounding it?
Zona pellucida
