L04: Ovarian Function Flashcards
Is the first 7 weeks of embryonic development different in females and male
No
When do PGCs arise
Week 3
Where do PGCs arise from
Epithelium of yolk sac
What happens between week 3 and 7
PGCs migrate to gonadal ridges and undergo mitosis (proliferation)
What is migration of PGCs mediated by
Chemotaxis: TGF-beta
Where are chemotaxis from
Gonadal ridges that attract the PGCs
From week 7 onwards what determines if the embryo is male or female
SRY gene that is expressed on the Y chromosome for males
Absence of Y chromosome develops female gonads
What are the female gonads
Ovary
Describe the process of ovary formation when PGCs migrate
1) Sex cord cells do not penetrate deeply and cluster around the PCGS to from primordial follicles
2) Sex cord cells then from granulosa cells (i.e Sertoli cells like in male)
3) Mesonephric cells that migrate from the vasculature to form theca cells in families (i.e leydig cells in males)
Is there any endocrine activity in ovarian development unlike the male foetus
No
What is turners syndrome
When individuals only have one X chromosome so they cannot develop an ovary which requires 2 X chromosomes
What is the role of a ovary after puberty
Produce eggs
Produce hormones
What is the male equivalent of primordial germ cells
Primordial germ cells
When PGCs are at the gonadal ridges what are PCGS termed as
Oogonium
What is the male equivalently oogonium
Spermatogonia
What is the female equivalent of primary spermatocytes
Primary oocyte
What is the female equivalent of secondary spermatocytes
Secondary oocyte
What has to occur to go from primary oocyte to secondary occyte
Meiosis
Which is the female equivalent of spermatozoa
Mature oocyte
What do secondary oocyte undergo to become haploid
2nd meiotic division
What is the difference between the the timing of spermatogonesis and Oogenesis
Males undergo meiosis post puberty
Females enter meiosis during fetal development
Which gene in females controls the entry of meiosis in
STRA8
What is this gene regulated by
Retinoic acid
Why doesn’t meiosis occurs in the male embryo
The embryo testis expresses cytochrome p450 that is mediated by breaking retinoic acid therefore we do no get a build up of retinoic acid in males
What is the difference between oogenesis and spermatogenesis in terms of being continuous
Males: spermatogenesis is continous when it starts after puberty
Females: 1st meiotic block just before ovulation, 2nd meiotic block after ovulation, meiosis completes post fertilisation.
Which oocyte is at rest in the 1st meiotic block
Primary oocyte at prophase 1
Which oocyte is in the 2nd meiotic block
Secondary oocyte at metaphase 2
If the primary oocyte remains in the 1st meiotic block what are they prone to
Damage
What is the difference with the number of sperm and egg produced
Males: have as spermatogonia (stem cells) that self renew so they produce sperm until end of life
Females: all oogonia enter meiosis before birth and there are no ovarian stem cells. A girl is born with the number of eggs she will have for the rest of her life.
What is the difference in number of eggs at different stages of life
Female germ cells undergo proliferation and then atresia (reduction) before birth
What is menopause a consequence of
Depletion of oocyte reservoir
What is climacteric
A period of reproductive changes that precedes menopause
What are the symptoms women can experience before menopause
Oligomennorhea
Mood changes
Loss of libido
Hot flushes
What is the definition of menopause
12 months without period if over 50
Or
24 months without periods if under 50
What happens to the levels of oestrogen during menopause
Decrease
What are the consequences of oestrogen withdrawal
Loss of anti-PTH: osteoporosis
Change in lipid ratio: coronary thrombosis
Reduction in vaginal lubrication: painful intercourse
Mood changes
How do we treat menopausal symptoms
Hormone replacement therapy
In hormonal replacement therapy what hormones do we give
Oestrogen
Progesterone
Why can you not give oestrogen without progesterone
It will lead to endometrial hyperplasia (endometrial cancer)
What is the difference in male and female meiotic division
They are asymmetrical
What 2 products does the 2nd meiosis of the secondary oocyte in females results in
Mature oocyte
Polar body
What is the polar body
Excess genetic material
How many polar body is released for each 2 meiosis
2 polar bodies in total
What are granulosa cells in females equivalent to in females
Sertoli cells
What are theca cells equivalent to in males
Leydig cells
What is the development of ovary follicles called
By folliculogenesis
What does sex cord cells cluttering around PGCs form
Primordial follicles
Until what stage does primordial follicles remains
Puberty
What happens during puberty to the primordial follicles
Grow each dayt
As primordial follicles grow what do they become
Primary follicle
What happens to the granulosa cells within the primordial follicle to become primary follicle
Granulosa cells become cuboidal
What happens to the outer layer of the egg during primary follicle development
Zona pellucida forms
How does the primary follicle form into the secondary follicle
Granulosa cells proliferate
Theca cells form 2 layers outside: theca interna and theca externa
What is the development of theca interna and theca externa dependent on
FSH signal
What happens when secondary follicle forms the tertiary follicle
1) Granulosa cells secrete follicular fluid
2) Follicle fluid fills the antrum (space around oocyte)
3) egg becomes surrounded by granulosa cells and fluid= Corona radiata
4) outside the corona radiata we have the cumulus cells (specialised granulosa cells)
At puberty when GNRH acts on the anterior pituitary gland what hormone is releases
LH
FSH
What receptor does FSH act on
FSHR
What does FSH stimulate
Follicle development
What receptor does LH act on
LHCGR
What does LH stimulate
Follicle maturation
Ovulation
Development of corpus luteum
What are the 3 hormones produced by the ovaries
Oestrogen
Progesterone
Cytokine: inhibin
What is progesterone produced by
Corpus luteum after ovulation
What is the role of progesterone
Preparation and maintenance endometrium for pregnancy
What is the role of estrogen
Development of secondary sex characteristic
Thinking of endometrium
Follicle maturation
What hormone is the 2 cell hypothesis
Oestrogen
Describe the 2 cell hypothesis
1) Theca cells release testosterone
2) testesterone diffuses into the follicle to become taken up by granulosa cells
3) granulosa cells express enzyme called aromatase
4) aromatase converts testerone to estorgen
5) LH acts on theca cells to increase cholesterol and produce testosterone
6) FSH acts on granulosa cells to increase aromatase enzyme
What are the 3 phases of the menstrual cycle
Proliferative/follicular
Ovulation
Secretory/luteal
Describe the process that occurs in the follicular/proliferative phase
1) hypothalamus secretes GNRH
2) GNRH acts on anterior pituitary gland so cause release of FSH
3) FSH rescues 15 follicles
4) in the growing follicles granulosa and theca cells develop to produce oestrogen
5) oestrogen that is produced at moderate level, suppresses FSH so you end with one dominant follicle
6) granulosa cells in the dominant follicle work with theca cells to produce more oestrogen and cause expression of LHCGR
7) high levels of oestrogen cause LH release from anterior pituitary gland
8) LH surge leads to ovulation
Describe the process that occurs in ovulation
1) LH sry gene leads to completion of meiosis 1
2) so secondary oocyte enters meiosis 2 but is at arrest at metaphase until fertilisation
3) there is an increase in follicular fluid and granulosa cells
4) follicle wall weakens
5) everything ruptures due to increased pressure
12) cumulus- oocyte complex ovulates and is picked up by fimbrae.
What happens at the luteal/secretory phase
1) corpus luteum (remain of follicle) undergo changes called lutenaisation
2) granulosa cells become large lutein cells and secrete progesterone and oestrogen
3) theca cells become small lutein cells and also secrete progesterone and oestrogen
16) under action of progesterone the endometrium becomes secretory to receive a fertilised egg if there is one
17) high levels of progesterone and oestrogen create a negative feedback so FSH/LH levels are low
What hormone is produced if fertilisation has occurred and there is pregnancY
HCG
Where does HCG act on
LHCGR on lutein cells to maintain corpus luteum
Why is it important to maintain the corpus luteum
Corpus luteum produces progesterone and oestrogen
What do high levels of progesterone and oestrogen do
Suppress ovulation
What happens after 6 weeks to the corpus luteum
Degenerates to from corpus albicans
Why does the corpus luteum degenate after week 6 of pregnancy
Placenta takes over
If there is no pregnancy what happens to the corpus luteum
Degenerates into the corpus Albicans
What happens to the progesterone and oestrogen levels if there is no pregnancy
Decrease
What does a fall in progesterone and oestrogen do
Remove Negative feedback and cycle continous
What does loss of progesterone cause
Menstruration
