Anatomy, Hormones, Puberty, Menstrual Cycle Flashcards
What releases gonadotrophin-releasing hormone (GnRH)?
Hypothalamus
What does GnRH do?
Stimulates the anterior pituitary to produce LH and FSH
What cells secrete oestrogen?
Theca granulosa cells around the follicles in the ovaries
What effect does oestrogen have on the hypothalamus and anterior pituitary?
Negative feedback effect to suppress the release of GnRH, LH and FSH
What stimulates the production of oestrogen?
LH and FSH
What is the most prevalent and active version of oestrogen?
17-beta oestradiol
List 4 actions of oestrogen.
- Breast tissue development
- Development of female sex organs at puberty
- Blood development in uterus
- Development of endometrium
What is progesterone produced by?
Corpus luteum
When is progesterone produced?
After ovulation
When pregnancy occurs, what mainly produces progesterone from 10 weeks gestation onwards?
Placenta
What is the action of progesterone (3)?
Acts on tissues previously stimulated by oestrogen:
- Thickens and maintains endometrium
- Thickens cervical mucus
- Increases body temperature
At what age does puberty start in girls?
8-14
At what age does puberty start in boys?
9-15
How long does puberty usually take from start to finish?
4 years
Why do overweight children tend to enter puberty at an earlier age?
Aromatase is an enzyme found in adipose (fat) tissue, that is important in the creation of oestrogen.
Therefore, the more adipose tissue present, the higher the quantity of the enzyme responsible for oestrogen creation.
List 4 situations where puberty might be delayed in girls.
- Low birth weight
- Chronic disease
- Eating disorders
- Athletes
In what order does puberty occur in girls?
- Development of breast buds
- Development of pubic hair
- Menarche
What scale is used to assess the stage of pubertal development in girls?
Tanner Staging
How many stages are there in Tanner Staging?
5
Describe Tanner Stage 1.
- ~Under 10 years
- No pubic hair
- No breast development
Describe Tanner Stage 2.
- ~Aged 10-11
- Light and thin pubic hair
- Breast buds form behind the areola
Describe Tanner Stage 3.
- ~Aged 11-13
- Course and curly pubic hair
- Breast begins to elevate beyond the areola
Describe Tanner Stage 4.
- ~Aged 13-14
- Adult like but not reaching the thigh
- Areola mound forms and projects from surrounding breast
Describe Tanner Stage 5.
- ~Above age 14
- Hair extending to the medial thigh
- Areolar mounds reduce, and adult breasts form
When during puberty does growth hormone increase?
During the initial phases of puberty, causing a growth spurt.
Describe how the hypothalamus starts to secrete GnRH.
Initially secretes during sleep, then throughout the day in later stages of puberty.
Describe what happens to FSH during puberty.
Plateaus about a year before menarche.
Describe what happens to LH during puberty.
LH rises and spikes just before menarche.
What are the two phases of the menstrual cycle?
Follicular and luteal.
When is the follicular phase?
The first 14 days in a 28 day cycle (from the start of menstruation to the moment of ovulation).
When is the luteal phase?
The final 14 days of the cycle (from the movement of ovulation to the start of menstruation).
What are cells that have the potential to develop into eggs called?
Oocytes.
What cells surround oocytes, forming follicles?
Granulosa cells.
Name the 4 stages of follicle development.
- Primordial follicles
- Primary follicles
- Secondary follicles
- Antral follicles (Graafian follicles)
When does the process of primordial follicles maturing into primary and secondary follicles occur?
It is always occurring, independent of the menstrual cycle.
At what stage do follicles develop the receptors for FSH?
Once they reach the secondary follicle stage.
What is required for further follicle development after the secondary follicle stage?
FSH
What do the granulosa cells secrete?
Oestrodiol
What effect does rising oestrogen have on cervical mucus?
Makes it more permeable, allowing sperm to penetrate the cervix around the time of ovulation.
What is the name of the follicle which develops more than the others?
Dominant follicle
When does LH spike?
Just before ovulation.
When does ovulation occur in the menstrual cycle?
14 days before end of cycle (e.g. day 14 of 28-day cycle, or day 16 of 30-day cycle).
What does the follicle that has release the ovum at ovulation become?
Corpus luteum
What does the corpus luteum secrete?
High levels of progesterone and small amount of oestrogen.
What part of the embryo secretes human chorionic gonadotrophin (HCG)?
Syncytiotrophoblast
What is the role of HCG?
Maintains the corpus luteum.
What triggers the endometrium to break down? (2)
- If there is no fertilisation, there is no HCG therefore corpus luteum degenerates and stops producing oestrogen and progesterone
- Stromal cells of endometrium release prostaglandins which encourage endometrium to break down and uterus to contract
What happens to the endometrium during menstruation?
Superficial and middle layers separate from basal layer.
How long does menstruation usually last?
1-8 days
