Lecture 37 Flashcards
What are the stem cells that produce oocytes?
oogonia
Is an oogonia cell haploid or diploid?
Diploid (2n = 46)
What does oogenesis require?
mitosis and meiosis
When is oogenesis initiated?
Before birth
What does oogenesis supply?
A life time supply of gametes produced before birth
Where do the oocytes develop?
Within ovarian follicles
How does the population of oogonia cells increase?
Via mitosis which stops before birth
What do oogonia differentiate into?
Primary oocytes
Are primary oocytes haploid or diploid?
Diploid (2n = 46)
What is the primary oocyte encased by?
The primary follicle
What happens to many of the primary oocytes?
They undergo atresia, a form of apoptosis
What do primary oocytes initiate?
Meiosis
Where does meiosis halt?
Prophase 1
When does meiosis procede?
At the beginning of puberty
What is menarche?
The first menstrual cycle
When puberty is reached, how many oocytes do females have?
~300,000
What happens in meiosis 1 after puberty has begun?
The primary oocyte will divide into a secondary oocyte and the first polar body
Is the secondary oocyte haploid or diploid?
Haploid (n)
What is a polar body?
A small haploid cell that cannot be fertilised and dies
What starts meiosis 2?
The secondary oocyte
Where does meiosis 2 halt?
At metaphase 2
When does meiosis 2 procede?
When fertilised - when the sperm penetrates the plasma membrane of the ovum
What happens to the secondary oocyte if fertilisation does not occur?
It will degenerate and undergo atresia, not completing meiosis
What does one primary oocyte ultimately form?
One ova and three polar bodies
Where does oogenesis occur?
Within the developing follicle
What are follicles?
Multilayered cell systems containing oocyte
What are the two types of cells within the follicle?
Granulosa and theca cells
What do granulosa cells produce?
Estradiol which surrounds oocyte
What is ovulaition?
When the oocyte and corona radiata are released into the peritoneal cavity
What is the female reproductive hormone released from the hypothalamus?
Gonadotropin-releasing hormone (GnRH)
What does GnRH do?
Stimulates release of follicle simulating (FSH) and luteinising hormone (LH)
Where is FSH and LH released from?
The anterior pituitary gland
What does FSH do?
Stimulates the growth of ovarian follicles
What does LH do?
Is involved in ovulation; the formation of the corpus luteum
What hormones do the ovary follicles secrete?
Estradiol (an estrogen) and inhibin
What hormones do the ovary corpus luteum secrete?
Inhibin and progesterone
What does estradiol do?
Assists follicle growth, bone and muscle growth, endometrial growth and secondary sex characteristics
Feeds back to anterior pituitary
What does inhibin do?
Negative feedback to anterior pituitary to suppress FSH
What does progesterone do?
Negatively feeds back to hypothalamus to suppress GnRH (therefore LH and FSH too). Also involved in endometrial maturation and maintains the pregnant state
What is the purpose of the ovarian cycle?
To prepare an oocyte for fertilisation and the endometrium for embryo implantation
When does menarche occur?
Around 12-13 years old
What is one part of puberty orchestrated by?
The increase in sex steroid production (estrogens) by the gonads
What happens in menopause?
The reduction of estradiol and progesterone due to the absence of or lack of response by follicles. The anterior pituitary feedback is no longer active and therefore FSH and LH are high
What is the follicular phase?
The preovulatory phase; day 1 - 14
What is the luteal phase?
The postovulatory phase; day 15 - 28
What happens during the follicular phase?
Increase FSH stimulates follicular growth, which secretes estradiol and inhibin in turn reducing FSH from negative feedback. Growing follicles undergo atresia, except dominant. High estradiol stimulates a surge of LH from positive feedback, the follicle ruptures and ovulation occurs - oocyte enters the peritoneal space
What happens during the luteal phase?
Ovulated follicle collapses and forms corpus luteum which secretes progesterone, estradiol and inhibin. These all negatively feedback to the hypothalamus, decreasing FSH and LH secretion.
What happens in the luteal phase if fertilisation and implantation do not occur?
The corpus luteum involutes (luteolysis), there is a fall in progesterone and estradiol and the negative feedback on the hypothalamus is removed. FSH and LH increase again for the cycle to begin again.
What is the menstrual and proliferative phase?
Day 1-14 for the endometrium
What is the secretory / premenstrual phase?
Day 15 - 28 for the endometrium
What happens in the menstrual and proliferative phase?
Endometrium breaks down and bleeds during menstruation. Estradiol stimulates endometrial growth from days 6-14and rapid tissue growth occurs including the growth of glands and vasculature
What happens in the secretory phase?
After ovulation (day 14) corpus luteum secreted progesterone which promotes endometrial maturation. Glands become secretory and spiral arterioles grow and coil
What happens at the end of the secretory phase if fertilisation does not occur?
Corpus luteum atrophies, progesterone levels fall and spiral arteries contract. Endometrial tissue breaks down and bleeding occurs. Shed tissue and blood removed via cervix and vagina
