lecture 37 - female reproductive system 2 Flashcards
What is oogenesis?
Formation and development of the oocyte (female gamete) from oogonia
What are oogonia?
Immature female sex cells that give rise to primary oocytes via mitosis
What process is undergone by oogonia to form primary oocytes?
Mitosis
When are female gametes first produced?
Before birth
What do oocytes develop within?
Ovarian follicles
Is mitosis or meiosis involved in oogenesis?
Both - first mitosis and then meiosis in several stages
What is the name for the ‘stem cell’ that is contained within the ovary and gives rise to primary oocytes via mitosis?
Oogonium (pl. oogonia)
What does an oogonium give rise to during mitosis?
1 oogonium and a diploid primary oocyte
Are primary oocytes diploid or haploid?
diploid (2n)
What process is undergone by a primary oocyte?
DNA replication then meiosis 1
What are the products of meiosis 1 of a primary oocyte?
First polar body and a secondary oocyte
Are secondary oocytes diploid or haploid
Haploid (n)
What differentiates a secondary oocyte from the first polar body?
Secondary oocyte will under meiosis 2 to form an ovum, while the first polar body will not. Secondary oocyte has the organelles and cellular components needed for these processes.
What phase of meiosis is a secondary oocyte in when it is released during ovulation?
Metaphase II
What form is an oocyte in when it is released during ovulation?
As a secondary oocyte in metaphase of meiosis 2
Under what condition will a secondary oocyte/ovum complete meiosis II?
If fertilisation takes place
When is the population oogonia produced, and how?
Produced before birth only, via mitosis
What are primary oocytes encased in?
Primordial follicles
What process is undergone by the majority of primary oocytes that are unsuccessful in developing?
atresia
What is atresia?
The degeneration of follicles/oocytes that are not dominant during ovulation
What is the final state of gametes before birth?
primary oocytes at prophase 1 of meiosis
At what stage of meiosis do primary oocytes halt before birth and until puberty begins?
Meiosis 1 - prophase 1
How many oocytes do females have when they first undergo puberty?
300,000
What is menarche?
The fist occurrence of menstruation
What is menopause?
The cessation of menstruation
What hormone influences the recruitment os a small number of follicles in each ovarian cycle?
GnRH - Gonadrotropin releasing hormone
What follicle is the successful oocyte for an ovarian cycle contained within?
The dominant follicle
When does a primary oocyte complete meiosis 1?
During ovulation when it is within a recruited dominant follicle, will complete meiosis 1 to form a secondary oocyte (haploid) and the 1st polar body
When is a second polar body formed?
When it undergoes meiosis 2 alongside the secondary oocyte, though this may not always happen
When does meiosis 2 resume in a secondary oocyte released from an ovary and is fertilised?
When the sperm penetrates the plasma membrane of the ovum at fertilisation.
What happens to a secondary oocyte that is ovulated but never fertilised
Will degenerate in a process called atresia
How many polar bodies ultimately form from one primary oocyte?
3 - plus one ova
What are the inner cells of a follicle?
granulosa cells
What are the outer cells of a follicle?
Theca cells
What do the granulosa cells of follicles in the ovaries produce?
Estradiol and inhibin
Where is estradiol produced in a follicle?
The inner layer of granulosa cells
What part of a follicle is released from the ovary with the oocyte during ovulation?
The corona radiata
What are the 6 key female reproductive hormones?
GnRH, FSH, LH, Estradiol, Inhibin, Progesterone
What is the role of FSH in the female reproductive system?
Stimulates the growth of ovarian follicles
What is the role of LH in the female reproductive system?
A surge of LH is involved in the stimulation of ovulation and then LH causes the formation of the corpus luteum.
What is the role of estradiol in the female reproductive system?
Assists in follicle growth, bone and muscle growth, endometrial growth, secondary sex characteristics, feedback to anterior pituitary a
What hormones negatively feedback to the anterior pituitary (to reduce LH and FSH secretion) in the female reproductive system?
Estradiol, inhibin
What hormone/s negatively feedbacks to the hypothalamus to inhibit GnRH release in the female reproductive system?
Progesterone
What are the functions of progesterone?
Negatively feedback to suppress GnRH production (and therefore decrease FSH and LH production), endometrial maturation, maintains pregnant state
What hormones are involved in endometrial growth and maturation?
Estradiol, progesterone
What are the 2 key cycles in the female reproductive system?
The ovarian and menstrual cycles
What is the function of the ovarian cycle?
To prepare an oocyte/ova for fertilisation
What is the purpose of the menstrual cycle?
To prepare the endometrium for embryo implantation
What is menarche orchestrated by?
An increase in sex steroid production (estrogens) in the gonads
What hormones are reduced during menopause?
Estradiol and progesterone
Why are estradiol and progesterone reduced during menopause?
There is a lack of response by follicles, meaning none of these hormones are secreted by the developing follicles
What is the effect on FSH and LH during menopause?
Decreased estradiol means less negative feedback to the anterior pituitary, resulting in high levels of FSH and LH
What are the 2 phases of the ovarian cycle?
Follicular/preovulatory, Luteal/post ovulatory
How many days is the ovarian cycle?
28 days approx.
What days of the ovarian cycle is the follicular phase?
Day 1-14
What days of the ovarian cycle is the luteal phase?
Days 15 - 28
How do FSH levels change during the follicular stage of the ovarian cycle?
Increase to stimulate follicular growth - help recruit a small cohort of follicles
How do estradiol levels change during the follicular stage of the ovarian cycle?
Increase as the growing follicles secrete estradiol
How do inhibin levels change during the follicular stage of the ovarian cycle?
Increase as the growing follicles release inhibin
What causes the decrease of FSH during the follicular stage of the ovarian cycle?
Estradiol and inhibin, though originally stimulated by FSH, inhibit FSH secretion via negative feedback on the anterior pituitary.
What is the result of high estradiol levels (released by the dominant follicle) in the follicular phase of the ovarian cycle?
Stimulates a surge of LH via positive feedback
What causes the surge of LH at the end of the follicular phase of the ovarian cycle?
Estradiol released by the follicle increases LH by acting on the anterior pituitary via positive feedback
When does ovulation occur, in terms of the ovarian cycle?
At the end of the follicular phase, due to a large surge in LH caused by high estradiol levels.
What occurs during the ovulation event?
Follicle ruptures, there is a release of fluid and then the oocyte, which enters the peritoneal space and then uterine tube.
What happens to the ovulated follicle during the luteal phase of the ovulatory cycle?
Ovulated follicle collapse and forms the corpus luteum and then corpus albicans
What does the corpus luteum secrete during the luteal phase of the ovarian cycle?
Progesterone, estradiol and inhibin
How do progesterone levels change during the luteal stage of the ovarian cycle?
Increase to peak then decrease again
How do estradiol levels change during the follicular stage of the ovarian cycle?
Increase to peak then decrease again
How do inhibin levels change during the follicular stage of the ovarian cycle?
Increase to peak then decrease again
What is the result of increase estradiol and inhibin at the very beginning of the luteal phase of the ovarian cycle?
Decrease FSH and LH via negative feedback to the anterior pituitary. This causes negative feedback to the hypothalamus, decreasing GnRH release.
How do GnRH levels change during the luteal stage of the ovarian cycle, assuming fertilisation do not occur?
decrease from peak and then slight increase at the end
How do LH levels change during the follicular stage of the ovarian cycle, assuming fertilisation does not occur?
Decrease from peak then slight increase at the end
How do FSH levels change during the follicular stage of the ovarian cycle, assuming fertilisation does not occur?
decrease from peak then slight increase at end
What happens to the corpus luteum if fertilisation and implantation do not occur?
The corpus luteum involutes (decreases in size via cell death) via luteolysis to form the corpus albicans
What are the 3 phases of the menstrual/endometrial cycles?
Menstrual, proliferative, secretory
What days of the menstrual cycle do the menstrual and proliferative phases fall on?
Days 1-14
What days of the menstrual cycle does the secretory phase fall on?
Day 15-28
What happens during the menstrual phase of the menstrual cycle?
From days 1-6, the endometrium breaks down and bleeds during menstruation
What happens during the proliferative phase of the menstrual cycle?
Estradiol stimulates endometrial growth from days 6-14 (approx.) of the cycle
What hormone stimulates endometrial growth during the proliferative phase of the menstrual cycle?
Estradiol
What key features of the endometrium grow during the proliferative phase of the menstrual cycle?
Glands and vasculature - spiral arterioles
How do estradiol levels change during the menstrual phase of the menstrual cycle?
Remain fairly constant - are low because not in proliferative phase yet
How do inhibin levels change during the menstrual phase of the menstrual cycle?
remain fairly constant and low - follicle is still in early stage of development so excretion is small
How do progesterone levels change during the menstrual phase of the menstrual cycle?
remain fairly constant and low
How do estradiol levels change during the proliferative phase of the menstrual cycle?
Increase to stimulate endometrial growth
How do inhibin levels change during the proliferative phase of the menstrual cycle?
Increase as the follicle continues to grow
How do progesterone levels change during the proliferative phase of the menstrual cycle?
increase slightly towards the end
How do estradiol levels change during the secretory phase of the menstrual cycle?
Peaked at the beginning of the phase then decrease before a smaller peak in the middle
How do progesterone levels change during the secretory phase of the menstrual cycle?
Peak in the middle of the phase
How do inhibin levels change during the secretory phase of the menstrual cycle?
Peak in the middle of the phase
Why do progesterone levels increase during the secretory phase of the menstrual cycle?
Coincides with corpus luteum formation after ovulation. Corpus luteum secretes progesterone for endometrial maturation in the secretory phase
What is the function of progesterone in the secretory phase of menstruation?
Promotes endometrial maturation, gland secretion and spiral arterioles growth
What happens at the end of the secretory phase of the menstrual cycle if fertilisation and implantation do not occur?
Corpus luteum atrophies, progesterone levels off (because will otherwise remain high to facilitate a pregnancy), spiral arteries contract, endometrium breaks down and is shed via the cervix and vagina.
