Reproductive System: Female Sex Hormones, Puberty, Menstrual Cycle, Ovulation, Conception & Implantation Flashcards
What hormones are released by the hypothalamus?
- TSH
- GnRH
- CRH
- GHRH
- Somatostain
- Dopamine
These then travel to the anterior pituitary.
What does GnRH stimulate the anterior pituitary to release?
LH and FSH
What is role of FSH and LH ?
Stimulate the development of the follicles in the ovaries (which then secrete oestrogen)
What hormone does theca granulosa cells around the follicles secrete?
Oestrogen
What is the effect of oestrogen on the hypothalamus & pituitary?
Negative feedback - suppresses releases of GnRH, LH and FSH
What is oestrogen?
Steroid sex hormone
What is oestrogen produced by?
Ovaries
What is oestrogen produced in response to?
LH and FSH
What is the most active version of oestrogen?
17-beta oestradiol
What is the action of oestrogen?
Acts on tissues with oestrogen receptors to promote female secondary sexual characteristics
* Breast tissue development
* Growth and development of the female sex organs (vulva, vagina, and uterus) at puberty
* Blood vessel development in uterus
* Development of endometrium
What is progesterone?
Steroid sex hormone
What is progesterone produced by?
Corpus luteum
When is progesterone produced?
After ovulation
What is progesterone produced by during pregnancy?
When pregnancy occurs, progesterone is produced mainly by the placenta from 10 weeks gestation onwards.
What is the action of progesterone?
Acts on tissues that have previously been stimulated by oestrogen and acts to:
* Thicken and maintain the endometrium
* Thicken the cervical mucus
* Increase the body temperature
What hormones increase during female puberty?
GnRH, LH, FSH, oestrogen and progesterone
How does being overweight affect puberty?
Overweight children tend to have puberty at earlier age
Why do overweight children tend to have puberty at earlier age?
Aromatase is an enzyme found in adipose tissue that is responsible for creation of oestrogen.
More adipose present –> higher quantity of aromatase –> more oestrogen
What enzyme is responsible for oestrogen creation?
Aromatase
Where is aromatase found?
Adipose tissue
What scale is used to determine the stage of pubertal development?
Tanner scale
What hormone causes a growth spurt during initial phase of puberty?
GH
When do FSH levels plateau?
About a year before menarche
What hormone induces menarhe?
LH
Describe LH levels during puberty
LH levels continue to rise and spike before they induce menarche
What 2 phases does the menstrual cycle consist of?
- Follicular phase
- Luteal phase
When is the follicular phase?
From start of menstruation to moment of ovulation (first 14 days in 28-day cycle)
When is the luteal phase?
from moment of ovulation to start of menstruation (final 14 days)
What forms a follicle?
Granulosa cells that surround oocytes
What are the 4 key stages of development that follicles go through in the ovaries?
- Primordial follicles
- Primary follicles
- 2ary follicles
- Antral follicles (Graafian follicles)
During which stage of development do follicles develop receptors for FSH?
Secondary follicles
Development of secondary follicles to antral follicles requires stimulation from what?
FSH
When does FSH stimulate further development of 2ary follicles?
At the start of the menstrual cycle
Note: one of the follicles will develop further and become the dominant follicle
As the follicles grow, the granulosa cells surrounding them secrete increasing amounts of what?
Oestradiol
What is the effect of oestradiol on the pituitary gland?
Negative feedback - reduces FSH and LH
How does oestradiol affect cervical mucus?
Rising oestrogen causes cervical mucus to become more permeable, allowing sperm to penetrate cervix around time of ovulation
What hormone spikes just before ovulation?
LH
What does the LH spike just before ovulation cause?
Causes the dominant follicle to release the ovum from the ovary
What is an ovum?
Unfertilised egg
When does ovulation occur in a 28 day cycle?
Day 14
When does ovulation occur in a 30 day cycle?
Day 16
After ovulation, the dominant follicle that released the ovum collapses and becomes what?
Corpus luteum
What does the corpus luteum then secrete? What is the purpose of this?
Secretes high levels of progesterone
- This maintains the endometrial lining
- Also causes cervical mucus to become thick and no longer penetrable
Secretes small amount of oestrogen
What is the effect of progesterone on cervical mucus?
causes cervical mucus to become thick and no longer penetrable
If fertilisation does occur, the syncytiotrophoblast of the embryo secretes what?
human chorionic gonadotrophin (hCG)
What is hCG produced by?
syncytiotrophoblast of the embryo
What is the effect of hCG on the corpus luteum?
Maintains it - without hCG, the corpus luteum degenerates
If there is no fertilisation, there is no production of hCG so what happens to the corpus luteum?
No production of HCG so corpus luteum degenerates and stops producing oestrogen and progesterone
If there is no fertilisation, the corpus luteum stops producing oestrogen and progesterone. What is the effect of this?
*Fall in oestrogen and progesterone causes endometrium to break down and menstruation occurs
If there is no fertilisation, what do the stromal cells of the endometrium release?
Prostaglandins
What are prostaglandins released by during the menstrual cycle?
Stromal cells of the endometrium
What is the effect of prostaglandins on the endometrium?
these encourage the endometrium to break down and uterus to contract (menstruation)
Once menstruation starts, what happens to the negative feedback from oestrogen and progesterone on. the hypothalamus & pituitary?
Ceases - allowing levels of LH and FSH to begin to rise, and cycle restarts
What day of the menstrual cycle does menstruation occur?
Day 1
Menstruation involves the separation of which layers of the endometrium?
Involves the superficial and middle layers of the endometrium separating from the basal layer
What does each primordial follicle contain?
A primary oocyte
What is an oocyte?
a germ cell (first generation of sex cell) that eventually undergoes meiosis to become the mature ovum, ready for fertilisation (i.e. they contain the full 46 chromosomes)
What do primordial follicles grow and become?
1ary follicle
What are the 3 layers of the 1ary follicle?
1) Primary oocyte in the centre
2) Zona pellucida
3) Cuboidal shaped granulosa cells
What do the granulosa cells secrete?
The granulosa cells secrete the material that becomes the zona pellucida. They also secrete oestrogen.
What do 2ary follicles grow and become?
2ary follicles
2ary follicle develops a single large fluid-filled area within the granulosa called what?
The antrum –> develops into antral follicle
What does an antrum refer to?
a natural chamber within a structure
What causes the antral follicle to expand rapidly?
The atrum fills with increasing amounts of fluid, making the follicle expand rapidly
What is the corona radiata?
Corona radiata is made of granulosa cells and surrounds the zona pellucida and the oocyte
One antral follicle becomes dominant and bulges through the wall of the ovary. What happens to the others?
They degrade
One antral follicle becomes dominant and bulges through the wall of the ovary. What happens then?
- Surge of LH from pituitary causes smooth muscle of theca externa to squeeze and follicle bursts
- Follicular cells also release digestive enzymes that puncture hole in wall of ovary –> ovum escapes
Oocyte is released into area surrounding ovary and is floating in peritoneal cavity but what is it quickly swept up by?
Fimbriae of fallopian tubes
The collapsed follicle becomes the corpus luteum. What do the cells of granulosa and theca interna become?
Luteal cells
What do the luteal cells secrete?
steroid hormones, most notably progesterone
What happens to the corpus lutuem if:
a) fertilisation occurs
b) fertilisation doesn’t occur
a) corpus luteum persists in response to HCG from a fertilised blastocyst
b) corpus luteum degenerates after 10-14 days
What hormone does the corpus luteum mainly secrete?
progesterone
Is the primary oocyte haploid or diploid?
Diploid (46 chromosomes)
Around the time of ovulation, what happens to the 1ary oocyte?
undergoes meiosis –> splits 46 chromosomes in the oocyte (diploid) into two, leaving only 23 chromosomes (haploid)
What happens to the other 23 chromosomes after the 1ary oocyte undergoes meiosis?
Become polar body (2ary oocyte)
Describe the structure of the ovum after the first polar body has been formed
o Middle is the oocyte with the first polar body
o Surrounded by zona pellucida
o Then surrounded by the granulosa cells that make up the corona radiata
Fertilisation:
1) Sperm enters fallopian tube
2) Attempts to penetrate corona radiata and zona pellucida – usually only one gets through before surrounding layers shut others out
3) Sperm enters egg and the 23 chromosomes of the egg multiple into two sets of 23
a. One set of 23 combine with the 23 from the sperm –> forms diploid set of 46
b. Other set of 23 float off to become second polar body
What is the name of the fertilised egg?
Zygote
The zygote then divides rapidly to form what?
A morula (mass of cells) that then travels along the fallopian tube towards the uterus
When does the morula become a blastocyst?
Becomes blastocyst while travelling due to fluid-filled cavity gathering within group of cells
Describe the structure of a blastocyst
- Blastocyst contains main group of cells in the middle called the embryoblast
- Alongside the embryoblast is a fluid-filled cavity called the blastocele
- Surrounding the embryoblast and the blastocele is an outer layer of cells called the trophoblast
- At this point it gradually loses the corona radiata and zona pellucida
- When the blastocyst enters the uterus, it contains 100-150 cells
How many days after ovulation does the blastocyst reach the endometrium?
8-10 days
Describe implantation of the blastocyst in the endometrium
1) Cells of trophoblast (outer layer of blastocyst) undergo adhesion to the stroma (supportive outer tissue) of the endometrium.
2) The syncytiotrophoblast (the outer layer of the trophoblast) forms projections into the stroma.
3) The cells of the syncytiotrophoblast mix with the cells of the endometrium (stroma).
What is the outer layer of the blastocyst?
Trophoblast
What is the stroma?
The supportive outer tissue of the endometrium
What is the outer layer of the trophoblast?
The syncytiotrophoblast
During implantation, what do the cells of the stroma convert into?
Into a tissue called the decidua - this is specialised in providing nutrients to the trophoblast.
What is the role of the decidua?
It is specialised in providing nutrients to the trophoblast.
When on an US can you see foetal heart activity?
After 6-7 weeks
What is HCG produced by?
Produced by the syncytiotrophoblast (this occurs when the blastocyst implants on the endometrium).
Role of HCG in implantation?
HCG maintains the corpus luteum in the ovary, allowing it to continue producing progesterone and oestrogen.
What causes endometrial proliferation?
Oestrogen (hence also why oestrogen drives endometrial cancer)
When does the LH surge occur?
During ovulation
What does the corpus luteum produce?
Corpus luteum
What results in menses?
Corpus luteum dies –> drop in progesterone –> destablises endometrium –> period
How long is the luteal phase?
ALWAYS 14 days long (i.e. if a cycle is >28 days then only the follicular phase is longer).
