Lecture 37: FEMALE REPRODUCTIVE SYSTEM 2 Flashcards
What is oogenesis?
Formation and development of the oocyte from oogonia
What does oogenesis require?
Mitosis and meiosis
What is produced before birth?
A lifetime supply of gametes
When does oogenesis occur?
It is initiated before birth and continues between puberty and menopause
How is oogenesis described?
Cyclic (1 ovulation every 28 days on average)
Where do oocytes develop?
Within an ovarian follicle (stationary) - 1 oocyte per follicle
What is in the gonad before birth?
oogonium (diploid, 2n=46)
What happens to the population of oogonia?
They increase by mitosis (stops before birth)
What do oogonia do?
Differentiate to form primary oocytes (diploid, 2n=46)
What are primary oocytes encased in?
Primordial follicle
What happens with many primary oocytes?
They undergo atresia
What do primary oocytes start?
Meiosis
When does meiosis halt?
At prophase 1 until puberty begins
How many oocytes do females have at puberty?
Approximately 300,000
What happens under GnRH influence?
A small number of follicles recruited each ovarian/menstrual cycle
What does only one oocyte do?
Complete development and ovulate (within the dominant follicle)
What does the primary oocyte complete?
Meiosis 1 to form a secondary oocyte and first polar body (both haploid, n=23)
What does the secondary oocyte start?
Meiosis 2
When does meiosis 2 halt?
At metaphase 2 which is suspended until fertilisation
When does meiosis 2 resume?
When the sperm penetrates the plasma membrane of the ovum at fertilisation
What happens if the secondary oocyte is not fertilised?
It will degenerate by atresia and therefore never complete meiosis
What does one primary oocyte form?
1 ova and 3 polar bodies will also form which under go atresia
What are the layers of the follicles?
Granulosa cells inside and theca cells outside
What do granules cells produce?
Inhibin
What happens in ovulation?
Oocyte and corona radiata released into peritoneal cavity
What are the female reproductive hormones?
GnRH, FSH, LH, estradiol, inhibit and progesterone
Where is GnRH released from?
The hypothalamus
What does GnRH do?
Stimulate the release of FSH and LH
Where is FSH released from?
The anterior pituitary
What does FSH do?
Stimulate growth of ovarian follicles
Where is LH released from?
Anterior pituitary
What does LH do?
Surge of LH is involved in ovulation, formation of corpus luteum
Where is estradiol released from?
Developing follices
What does estradiol do?
Assists follicle growth (with FSH), bone and muscle growth, endometrial growth, secondary sex characteristics, feedback to anterior pituitary
Where is inhibin released from?
Granulosa cells
What does inhibit do?
Negative feedback to anterior pituitary to suppress FSH
Where is progesterone released from?
The corpus luteum
What does progesterone do?
Negatively feeds back to suppress GnRH (therefore LH and FSH), endometrial maturation, maintains pregnant state
What are 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
When does the menstrual cycle occur?
On approximately monthly basis (average 28 days) between menarche and menopause
What is menarche?
First menstrual period
When does menarche occur?
At age 12-13 on average
What is menarche part of?
Puberty - orchestrated by increase in sex steroid production (oestrogen’s) by the gonads
What is menopause?
Cessation of menstruation
When does menopause occur?
Typically in early 50’s
What is menopause caused by?
Reduction of estradiol and progesterone due to absence of or lack of response by follicles. Anterior pituitary negative feedback no longer active therefore FSH/LH high
What are the phases of the ovarian cycle?
follicular (preovulatory) phase and luteal (postovulatory) phase
When does the follicular phase occur?
Days 1-14
When does the luteal phase occur?
Days 15-28
What happens in the follicular phase?
Increased FSH from the anterior pituitary stimulates follicular growth
What do growing follicles secrete?
Estradiol and inhibin
What does growing follicles secreting estradiol and inhibin cause?
reduced FSH from anterior pituitary (negative feedback) and growing follicles undergo atresia (except the dominant follicle)
What does the dominant follicle secrete?
Large amounts of estradiol
What does high estradiol stimulate?
Surge of LH (positive feedback)
what happens because of the surge of LH?
The follicle ruptures and ovulation occurs
What happens in ovulation?
Oocyte enters peritoneal space/collected into uterine tube
What happens in the luteal phase?
Ovulated follicle collapses and forms corpus luteum
What does the corpus luteum secrete?
Progesterone, estradiol and inhibin
What do progesterone, estradiol and inhibin do?
Decrease FSH and LH secretion - negative feedback on hypothalamus
What happens if fertilisation and implantation don’t occur?
The corpus luteum involutes (luteolysis) and eventually forms the corpus albicans
What happens to hormones if fertilisation doesn’t occur?
A fall in progesterone and estradiol which removes negative feedback on FSH and LH so the cycle starts again
What are the phases of the menstrual cycle?
Menstrual and proliferative, then secretory
When do the menstrual and proliferative phases occur?
day 1-14
When does the secretory phase occur?
Day 15-28
What happens in the menstrual phase?
Endometrium breaks down and bleeds (from spiral arterioles)
What happens from approximately days 6-14 of the menstrual and proliferative phase?
Estradiol stimulates endometrial growth. Rapid tissue growth, including growth of glands and vasculature
What happens after ovulation (day 14)?
Corpus luteum secretes progesterone
What does progesterone promote?
Endometrial maturation
What happens in endometrial maturation?
Glands become secretory and spiral arterioles grow and coil
What happens if fertilisation and implantation do not occur?
Corpus luteum atrophies (breaks down), progesterone levels fall, spiral arteries contract, endometrial tissue breaks down and bleeding occurs, shed tissue and blood removed via cervix and vagina (menstruation/menses)
