Lecture 37: Female Reproduction II Flashcards
Define oogenisis
the formation and development of the oocyte from oogonia
Oogenesis required what two processes?
mitosis and meiosis
When is oogenesis initiated? When does it continue?
begins before birth
continues between puberty and menopause
Oocytes develop within what?
ovarian follicles
How many oocytes are in one follicle?
1
Define oogonium
an immature female reproductive cell that gives rise to primary oocytes by mitosis
Are oogonia diploid or haploid?
diploid (2n = 46)
How does the population of oogonia increase?
by mitosis
When does the population of oogonia increase and then stop?
all before birth
What do oogonia differentiate into?
primary oocytes
Are primary oocytes diploid or haploid?
diploid (2n = 46)
When do oogonia differentiate into primary oocytes?
before birth
What are oogonia encased in?
primordial follicle
Describe the events of oogenesis that occur before birth
Diploid oogonium increase in number by mitosis. Then they differentiate to form diploid primary oocytes which are encased in primordial follicles. These primary oocytes start meiosis and halt at prophase I until puberty begins
What is atresia? Give an example with numbers to explain
The number of eggs decreasing in number
eg. you are born with 700,000 eggs but by the time you reach puberty you only have about 300,000
Describe the events of oogenesis that occurs from menarche until menopause
Under GnRH influence, a small number of follicles grow but only one oocyte goes on to be released. Just before ovulation, the dominant oocyte completes meiosis I forming a secondary oocyte and a polar body. The secondary oocyte begins meiosis II and halts at metaphase II and it is suspended here until fertilisation.
What is the dominant follicle and oocyte?
the dominant follicle is the follicle containing the dominant oocyte which is the only oocyte which is released despite a number of them growing under GnRH influence each cycle
What is a polar body? Is it haploid or diploid?
When the primary oocyte completes meiosis I, it forms a haploid polar body (and a secondary oocyte) which contains all the same genetic information as the secondary oocyte but does not contain any other cellular contents.
When is a second polar body formed?
If the secondary oocyte is fertilised the it completes meiosis II to form an ovum and a haploid secondary polar body
When is a second polar body formed?
If the secondary oocyte is fertilised the it completes meiosis II to form an ovum and a haploid secondary polar body
What oocyte is contained in a primordial follicle?
primary
What oocyte is contained in a primary follicle?
primary
What is the oocyte contained in a secondary follicle?
primary
What is the oocyte contained in a tertiary follicle?
secondary
What is the order of follicle development?
primordial
primary
secondary
tertiary
Where does oogenesis occur?
within a developing follicle
The outer layer of a follicle are made of what two types of cells?
- granulosa cells
- theca cells
What do granulosa cells produce?
estradiol
What are corona radiata cells?
specialised granulosa cells
What is released during ovulation?
an oocyte, corona radiata and antrum (fluid) is released into pelvic cavity and collected up by the fimbriae
Primary oocytes start meiosis prior to birth but the process halts at __________ until puberty begins
prophase I
After puberty, small groups of follicles start to grow each ovarian cycle - only one of these oocytes in the follicle goes on to ovulate (the ________ follicle)
dominant
The dominant follicle begins meiosis II, but the process halts at ________ until fertilisation occurs
metaphase II
What are the six female reproductive hormones?
GnRH (gonadotropin releasing hormone) FSH (follicle stimulating hormone) LH (Luteinising hormone) Estradiol Inhibin Progesterone
Where is GnRH released?
hypothalamus
Where is FSH released?
the anterior pituitary
Where is LH released?
the anterior pituitary
Where is estradiol released?
from the granulosa cells in the follicles and corpus luteum
Where is inhibin released?
from the follicles and the corpus luteum
Where is progesterone released?
from the corpus luteum
What is the role of GnRH?
release of FSH and LH
What is the role of FSH?
it stimulates the growth of ovarian follicles
What is the role of LH?
there is a surge of LH involved in ovulation which leads to the formation of the corpus luteum
What is the role of estradiol? (5)
- assists follicle growth (with FSH)
- bone and muscle growth
- endometrial growth
- secondary sex characteristics
- feedback to anterior pituitary gland
What is the role of inhibin?
negative feedback to the anterior pituitary to suppress FSH
What is the role of progesterone?
- negative feedback to suppress GnRH (therefore LH and FSH)
- endometrial maturation
- maintains pregnant state
What does the ovarian cycle describe?
the cyclic changes in the ovary (development of oocyte and follicle) and formation of corpus luteum and corpus albicans
What does the menstrual/endometrial/uterine cycle describe?
the cyclic changes to the uterus
What is the purpose for the ovarian and menstrual cycles being cyclic?
to prepare the oocyte to be fertilised by taking it to the correct spot for that to occur and to prepare the endometrium for the possibility of embryo implantation
Define menarche
the first menstrual period
What orchestrates menarche?
an increase in sex steroid (oestrogens) production by the gonads
Define menopause
cessation of menstruation
What causes menopause?
There is a reduction of estradiol and progesterone due to absence of or lack of response by the follicles so the anterior pituitary feedback is no longer active so FSH and LH remain high
What are the two phases of the ovarian cycle?
follicular (preovulatory phase)
luteal (postovulatory phase)
What happens during the follicular (preovulatory phase) - days 1-14?
Prior to this there has been a decrease in progesterone levels which means that there is increased FSH released from the anterior pituitary. This stimulates follicular growth. There is a small number of follicles which produce estradiol and inhibin. This provides negative feedback to the hypothalamus and reduces the release of FSH from the anterior pituitary. Without FSH, the growing follicles undergo atresia, except the dominant follicle The dominant follicle secretes large amount of estradiol which stimulates the surge of LH by positive feedback which causes ovulation (oocyte in mature follicle with meiosis I complete and meiosis II halted at metaphase II). The follicle ruptures and the oocyte enters the peritoneal space to be collected into the uterine tube.
What happens during the luteal (postovulatory phase) - days 15-28?
The oocyte have been released but the follicle changes to form the corpus luteum. This produces progesterone, estradiol and inhibin which together provide negative feedback to the hypothalamus and anterior pituitary gland to keep GnRH low and to stop FSH and LH secretion.
If fertilisation and implantation do not occur, then the CL dies so progesterone, inhibin and estradiol levels decrease which removes the negative feedback on the hypothalamus and anterior pituitary gland do FSH and LH are released which starts the cycle again
What are the three phases of the menstrual (endometrial) cycle and on what days do these occur?
- menstrual phase then the proliferative phase (days 1-14)
- the secretory phase (and premenstrual phase) (days 15-28)
What occurs in the menstrual and proliferate phases?
The corpus luteum is breaking down in the ovarian cycle which decreases the levels of progesterone, estradiol and inhibin decrease. As the levels progesterone decrease, the endometrial layer breaks down and bleeds and then repairs in response to estradiol release. There is rapid tissue growth, including growth of the glands and vasculature.
What occurs first, the menstrual or proliferative phase?
the menstrual phase
What occurs in the secretory phase?
After ovulation, the corpus luteum secretes progesterone which promotes endometrial maturation. The glands become secretory and the spiral arterioles grow and coil. This is all in preparation for the possibility of implantation.
What happens in the secretory phase if fertilisation and implantation do not occur?
- the corpus luteum atrophies
- progesterone level fall
- spiral arteries contract
- endometrial tissue breaks down and bleeding occurs
- the tissue and blood removed via the cervix and vagina (this is the start of the menstrual phase again)
Secretions of large amounts of estradiol by the _________ ________ will cause the __________ and subsequently ovulation and formation of the corpus luteum
dominant follicle
LH surge
The endometrium undergoes cyclic periods of growth, maturation and breakdown in response to cyclic patterns in ________ and __________
progesterone
estradiol
