S4) The Menstrual Cycle Flashcards
1
Q
Group the menstrual cycle into 3 general stages and how many days does it last in average
A
- Preparation – ovarian & uterine cycle
- Ovulation – release of gamete
- Waiting – maintaining endometrium until fertilisation occurs
28 days
2
Q
Identify 2 types of hormones which control the menstrual cycle
A
- Gonadotrophins - FSH, LH
- Ovarian steroids OESTROGEN, TESTOSTERONE
3
Q
Where do gonadotrophins act?
A
Gonadotrophins act on the ovary
4
Q
What two actions do ovarian steroids do?
A
- Act on tissues of the reproductive tract
- Act to control the cycle
5
Q
In the HPO axis, what substance is produced by the hypothalamus?
A
GnRH
6
Q
In the HPO axis, what does GnRH do?
A
Acts on anterior pituitary to release gonadotrophins:
- FSH
- LH
7
Q
In the HPO axis, what do gonadotrophins do?
A
- Promoting follicular development
- Promote production of ovarian hormones
8
Q
Identify two types of ovarian hormones
A
- Steroid hormones
- Inhibin
9
Q
How is the HPO axis controlled?
A
- Controlled by effects of gonadal hormones
- Negative and positive feedback control
10
Q
Why is the pulsatile release of GnRH important?
A
- Intermittent GnRH receptor is required for fertility
- If GnRH receptors are exposed continuously to GnRH, they become desensitised and gonadotrophin production stops
11
Q
What are the stages in the ovarian cycle?
A
- Follicular phase (1-14) follicle develops
- ovulation day 14
- Luteal phase (14 days) corpus lute develops
12
Q
Describe the layout and actions of the HPO axis
A
13
Q
What is the main event occuring at the start of the menstrual cycle?
A
Early development of follicles begins
14
Q
Describe the hormone levels at the start of the menstrual cycle
A
- No ovarian hormone production
- Low steroid and inhibin levels
- FSH levels rising
15
Q
Describe the amount inhibition observed at the start of the menstrual cycle
A
Free from inhibition as there is little inhibition at the hypothalamus or anterior pituitary
16
Q
Describe the effects of FSH on the developing follicles
A
FSH binds to granulosa cells:
- Follicular development continues
- Theca interna appears
- Follicle now secretes oestrogen & inhibin
17
Q
What two things need to occur in the mid follicular phase?
A
- Nominate a dominant follicle
- Prevent recruitment of any further follicles
18
Q
Explain how FSH is inhibited by the developing ovarian follicle
A
- [Follicular oestrogen] now exerts positive feedback on the hypothalamus and anterior pituitary
- Selective inhibition of FSH occurs as only [LH] rises
- [Follicular inhibin] rises
19
Q
What 4 events occur in preparation for ovulation?
A
⇒ [Oestradiol and inhibin] rise rapidly
⇒ Oestradiol production independent of FSH
⇒ Surge in LH production
⇒ Modulation of GnRH pulse generator
20
Q
What causes the surge in LH?
A
- High [oestrogen] enhances sensitivity of anterior pituitary gonadotrophins to GnRH
- Selective inhibition of FSH leads to surge in LH
21
Q
What is the relationship between the surge in LH and the production of progesterone?
A
- LH causes the formation of the corpus luteum
- corpus luteum produces progesterone
- Granulosa cells become responsive to LH
22
Q
Identify 3 processes which occur during ovulation
A
- Mature oocyte extruded through the ovary capsule
- Meiosis I is completed
- Meiosis II commences
23
Q
Describe the hormone levels immediately after ovulation
A
- Follicle is luteinised and secretes oestrogen and progesterone in large quantities
- Inhibin continues to be produced and LH is suppressed
24
Q
Why is LH production suppressed after ovulation?
A
Negative feedback due to the presence of large quantities of progesterone
25
What characterises the waiting phase?
Further gamete development is suspended
26
In the luteal phase, what hormones are produced by the corpus luteum?
- Progesterone
- Oestrogen
- Inhibin
27
What causes the corpus luteum to regress?
The absence of a surge of LH
28
What are the two stages in the uterine cycle?
- Proliferative phase
- Secretory phase
29
What is the endometrium and what does it do?
- The **endometrium** is the lining of the uterus
- It is a **specialised epithelium** that responds to ovarian hormones
30
Explain how the uterus responds to the following:
- Oestrogen
- Progesterone
- Responds to oestrogen by **proliferating**
- Responds to oestrogen and progesterone by **secreting**
31
Label the following structures on the uterus below:
- **M** = myometrium
- **E** = endometrium
- **F** = functional layer
- **B** = basal layer
32
What is the myometrium?
The **myometrium** is the muscular wall of the uterus
33
What does the functional layer of the uterus do?
The **functional layer** is hormone responsive and sheds if no pregnancy occurs
34
What does the basal layer of the uterus do?
The **basal layer** provides the source from which a new functional layer is developed
35
Describe the appearance of the uterus during the early proliferative phase
**Early proliferative:** glands sparse, straight
36
Describe the appearance of the uterus during the late proliferative phase
**Late proliferative:** functional layer has doubled, glands now coiled
37
Describe the appearance of the uterus during the early secretory phase
**Early secretory:** endometrium max thickness, very pronounced coiled glands
38
Describe the appearance of the uterus during the late secretory phase
**Late secretory:** glands adopt characteristic "saw-tooth” appearance
39
What effect does the regression of the corpus luteum have?
- Dramatic fall in gonadal hormones relieves negative feedback
- Menstrual cycle starts again
40
What happens when fertilisation occurs?
- Syncytiotrophoblast produces **human chorionic gonadotrophin**
- Corpus luteum is maintained by placental hCG
41
What is the significance of human chorionic gonadotropin?
- Made by the embryo to signal its presence
- Exerts a luteinising effect
42
What role does the corpus luteum have in pregnancy?
- It produces steroid hormones to support the pregnancy
- It regresses once the placenta can produce sufficient quantities of steroid hormones to control the HPO axis
43
Illustrate the relationship between the ovarian and menstrual cycles
44
Identify the 6 effects of oestrogen in the follicular phase
- **Fallopian tube** function
- Thickening of **endometrium**
- Growth & motility of **myometrium**
- Thin alkaline **cervical mucus** forms
- **Vaginal** changes
- Changes in **skin, hair, metabolism**
45
Identify the 6 effects of progesterone in the luteal phase
- Further **thickening of endometrium** into secretory form
- **Thickening of myometrium** & reduction of motility
- Thick acidic **cervical mucus** forms
- Changes in **mammary tissue**
- Increased **body temperature**
- **Metabolic** and **electrolyte** changes
46
What is the normal duration of the menstrual cycle?
21 – 35 days
47
What causes variations in the menstrual cycle?
- Variation in the length of the **follicular phase**
- **Luteal phase** strictly controlled to 14 days (± 2)
48
Identify 4 factors which affect the menstrual cycle
- Pregnancy
- Lactation
- Emotional stress
- Low body weight
49
what is the general function of LH
* stimulates ovulation
* stimulates release of progesterone via corpus lute
50
what is the general function of FSH
* stimulates follicle to be produced
* and stimulates production of oestrogen
51
what is the role of oestrogen
* to thicken the uterine endometrium
* causes negative feedback on FSH and LH
*
52
role of Inhibin
* inhibit FSH
* so no more follicles can mature
53
role of progesterone
to maintain the thickness of the endometrium
54
outline the uterine cycle
1. menstrual cycle: day 1 when Period comes → end
2. proliferative stage: when the lining builds up
3. secretory phase: lining gets thicker
55
what is happening days 1-5 in the early follicular phase
* **FSH** and LH levels are at a **high**
* **granulosa cells** are secreting **activin** (increases FSH production)
* **follicle is now growing** and it releases more FSH to grow more
* **theca interna** appears (early stage of corpus lutenum)
* follicle is now capable of **oestrogen production**
* the **dominant follicle** starts producing **Inhibin** from activin which causes more **oestrogen** to be produced and also **stops development of other follicles**
56
what happens day 5-14 in the follicular phase
* dominant cells are producing **Inhibin and oestrogen**
* these levels continue to rise
* oestrogen:
* 1. increases **FSH** for **negative feedback** to stop more FSH
* 2. **increases LH** for preparation of ovulation
* Inhibin:
* 1.**reduces FSH** so no more follicles can develop
* 2. helps LH to increase theca cell **androgen production → oestrogen**
57
what occurs on day 14 - ovulation day
* **oestrogen** continues to **rise** independent of FSH (been inhibited)
* high levels of oestrogen exert **positive feedback**
* **Surge in LH** (not in FSH due to inhibin)
* **ovulation** occurs
* **progesterone** is released by granulosa cells
58
what occurs in the luteal phase
* **LH** tells the follicle to develop into **corpus luteum**
* oestrogen, progesterone and Inhibin are being secreted in high levels
* **progesterone** is the dominant hormone here
* endometrium prepares for **implantation**
* O+P exert **negative feedback on LH**
59
what is the lifespan of the corpus luteum
14 days
* it secretes progesterone
will either turn into tunica albicans if no implantation and period
or it implants
60
what happens at the end of the menstrual cycle
if no fertilisation:
* **corpus albicans**
* dramatic fall in all hormones
* **FSH rises**
* decrease in progesterone triggers menustration
if fertilisation:
* syncyriotrophoblasts produce **HCG**
* expands lifespan of corpus luteum
61
compare oestrogen to progesterone
oestrogen: thickening of endometrium
Fallopian tube function
Growth and motility of endometrium
Thin alkaline cervical mucus
changes skin, hair, metabolism
progesterone: maintains thickness of endometrium
thickening of mucus so no entrance of cervix
development of breast tissue
increased body temp, metabolic changes
oily skin, spots, bloated
62
what hormone levels do you check ti ensure that ovulation has occurred
* progesterone measure on day 21
