Lecture 37: Female reproductive system II Flashcards
What is Oogenesis?
The formation and development of the oocyte (female gamete) from oogonia
What is required to carry out Oogenesis?
2
- Mitosis
- Meiosis
How many gametes are produced and when are they produced for Oogenesis?
A lifetime supply of gametes are produced, before birth
When does Oogenesis begin?
Before birth but then halts until puberty
When oogenesis begins to continue again what time period does oogenesis occur between?
Between puberty (Menarche) and menopause
Between puberty and menopause how often does oogenesis occur?
1 ovulation every 28 days (on average) - cyclic
Before birth oogonium are what?
Diploid (2n=46 chromosomes) in gonads
How does the population of oogonia increase?
By mitosis (which stops before birth)
Oogonia differentiate to form what?
Primary oocytes (diploid, 2n=46 chromosomes)
What are Oogonia that differentiate to form primary oocytes encased by?
Primordial follicle
What do many primary oocytes undergo?
Atresia
What happens to primary oocytes that have formed?
They start meiosis
When do primary oocytes halt in meiosis
Prophase 1
After oocytes have halted at prophase 1 of meiosis when does it begin again?
When puberty begins
At puberty approximately how many oocytes do females have?
300,000
Under the influence of GnRH what happens each ovarian/menstrual cycle?
A small number of follicles are recruited
During a menstrual cycle what will happen to only one oocyte?
It will complete development and ovulate (within the dominant follicle)
What do primary oocytes that complete meiosis I form?
Secondary oocytes and 1st polar body (both haploid, n=23)
What do secondary oocytes start?
Meiosis II but it halts at metaphase II and is suspended until fertilisation
When do secondary oocytes continue meiosis II?
They resume meiosis II when the sperm penetrates the plasma membrane of the ovum at fertilisation
What happens to secondary oocytes that are not fertilised?
They will degenerate (atresia) and therefore never complete meiosis
Where does oogenesis occur?
Within developing follicle
What are follicles?
Multilayered granulosa/theca cells
What do granulose cells produce?
Estradiol
During ovulation what happens to the oocyte?
They are released into the peritoneal cavity with corona radiata
What does GnRH from the hypothalamus do?
Stimulate the release of FSH and LH
What does FSH from the anterior pituitary stimulate in ovarian follicles?
The growth of ovarian follicles
What does LH from the anterior pituitary stimulate?
A surge of LH involved in ovulation, formation of corpus luteum
What does estradiol from developing
follicles assist with?
(5)
- Follicle growth (with FSH)
- Bone and muscle growth
- Endometrial growth
- Feedback to anterior pituitary
- Secondary sex characteristics
What does inhibin from granulose cells do?
support negative feedback to anterior pituitary to suppress FSH
What does progesterone from the corpus luteum support?
2
- Negatively feeds back to suppress GnRH (therefore LH and FSH)
- Endometrial maturation or maintains pregnant state
What is the ovarian/menstrual cycles?
The regular cyclic changes in the ovary and uterus that prepare an oocyte/ova for fertilisation and the endometrium for embryo implantation
How often does the menstrual cycle occur?
Approximately monthly basis between menarche and menopause
What is menarche?
The first menstrual period
When does menarche occur?
At age 12-13 years on average
Menarche is the part of puberty orchestrated by what?
Increase in sex steroid production (oestrogen’s) by the gonads
What is menopause?
Cessation of menstruation
When does menopause typically occur?
In early 50’s
Menopause is a reduction of what in response to the absence of what?
The reduction of estradiol and progesterone due to the absence of or lack of response by follicles
What are the stages of the female reproductive cycle - Ovarian?
(2)
- Follicular (preovulatory phase) Day 1 - 14
- Luteal (postovulatory phase) Day 15 - 28
What happens to FSH during the follicular phase?
Increased FSH from the anterior pituitary
What does FSH from the anterior pituitary stimulate during the follicular phase?
Follicular growth
What do growing follicle secrete during the follicular phase?
Estradiol and inhibin
What does does estradiol and inhibin reduce during the follicular phase?
Reduces FSH from the anterior pituitary (negative feedback)
What does estradiol and inhibin cause the growing follicles to do in the follicular phase?
Atresia, except the dominant follicle
What does the dominant follicle secrete during the follicular phase?
Large amounts of estradiol
What does high estradiol stimulate during the follicular phase?
It stimulates a surge of LH (positive feedback)
During the follicular phase what happens to the dominant follicle following a surge of LH?
The follicle ruptures and ovulation occurs, oocytes then enters peritoneal space/collected into uterine tube
What happens to ovulated follicle during the luteal phase?
Ovulated follicle collapses and forms corpus luteum which secretes progesterone, estradiol and inhibin
What does the progesterone, estradiol and inhibin released from the ovulated follicle cause during the luteal phase?
They decrease FSH and LH secretion causing negative feedback on the hypothalamus
What happens in the luteal phase if fertilisation and implantation does not occur?
The corpus luteum involutes (luteolysis) causing a fall in progesterone and estradiol
What does a fall in progesterone and estradiol cause in the luteal?
Removal of negative feedback on FSH and LH causing the cycle to starts again
What are the stages of the Menstrual cycle?
2
- Menstrual and proliferative
- Secretory
What happens to the endometrium during the menstrual/proliferation phase?
It breaks down and bleeds during menstruation
What does estradiol stimulate?
Endometrial groth from approximately day 6-14
What happens during the menstrual and proliferation phase to tissue/glands/vasculature?
Rapid growth
What does the corpus luteum do during the secretory phase?
It secretes progesterone
What does progesterone promote during the secretory phase?
Endometrial maturation where glands become secretory and spiral arterioles grow and coil
What happens to the corpus luteum if fertilisation and implantation do not occur during the secretory phase?
It atrophies
What happens to progesterone levels if fertilisation and implantation do not occur during the secretory phase?
The progesterone levels fall
What happens to the spiral arteries if fertilisation and implantation do not occur during the secretory phase?
The spiral arteries contract
What happens to the endometrial tissue if fertilisation and implantation do not occur during the secretory phase?
It breaks down and bleeding occurs
What happens to the shed tissue and blood if fertilisation and implantation do not occur during the secretory phase?
It is removed via the cervix and vagina
