Reproductive endocrinology Flashcards
When does oogenesis begin, complete and cease?
Begins in utero, is suspended for many years and resumes at puberty
Completes with fertilisation
Ceases with menopause
What is oogonia?
Completion of last pre-meiotic division to oocytes
What happens at the start of each menstrual cycle to the primordial follicles?
Several follicles enlarge and a cavity forms around the ovum within the follicle called antrum formation
What is contained within each primordial follicle?
An immature ovum
What is the cavity around the ovum within the follicle during antrum formation filled with?
Follicular fluid
During which day of the menstrual cycle does a dominant follicle become apparent?
6th
What is the dominant follicle in menstruation?
At the start of the cycle, several follicles enlarge
One follicle in one ovary tends to grow more rapidly than the others in the first 6 days
The others regress, becoming atretic follicles
What is the first half of the menstrual cycle called?
Follicular phase
What happens during the follicular phase?
Maturation of egg, ready for ovulation at midcycle
What signals the end of the follicular phase?
Ovulation
What is the primary source of circulating estrogen?
The granulosa cells of the ovaries
At birth, what is the primary oocyte surrounded by?
A single layer of granulosa cells
What is a primary follicle?
The primary oocyte surrounded by a single layer of granulosa cells
How does the primary follicle become the secondary follicle?
Oocyte grows (x1000) and follicle expands and becomes differentiated under hormonal influence
What happens on about the 14th day of the cycle after the mature follicle has formed and the dominant follicle apparent?
The distended follicle ruptures and released the ovum into the abdominal cavity
This is ovulation
What happens to the ovum that has been ovulated into the abdominal cavity?
Picked up by the fimbrae of the uterine tube (oviducts) and transported along to the uterus and out through the vagina
(Unless fertilisation occurs)
What happens to the follicular cells left behind after ovulation?
Undergo lutenization to form the corpus luteum
What hormone does the corpus luteum secrete?
Progesterone
What is the main hormone secreted during the follicular phase?
Oestrogen
How long does the corpus luteum grow after ovulation?
For 8-9 days
What event signals the start of a new follicular phase?
The degeneration of the corpus luteum
It will survive no longer than 14 days after ovulation
What is growth of the corpus luteum dependant on?
Developing a blood supply
What happens to the corpus luteum if pregnancy occurs?
It persists and it secretes increasing quantities of oestrogen and progesterone until after delivery
At what time do ova undergo the first part of the first meotic division and what happens after this?
At birth
There are roughly 2 million ova at this point, with 50% being atreic
The normal ones undergo the first part of the first meiotic division, and arrest in prophase in which those that survive persist into adulthood
At what time do ova complete the first meiotic division?
Just before ovulation
What happens to the daughter cells of the first meiotic division?
One, the secondary oocyte, recieves most of the cytoplasm
The other, the first polar body, fragments and disappears
When does the start of the second meiotic division occur and in which cells?
The second meiotic division only occurs in the secondary oocyte: the surviving daugther cell from the first meiotic division
Second meiotic divison occurs almost immediately after the first, but is arrested at metaphase
When is the second meiotic division completed?
When a sperm penetrates the oocyte
This casts off the second polar body and the fertilised ovum proceeds to create a baby
Which hormone stimulates the anterior pituitary to produce ovarian hormones?
GnRH
What are the reproductive hormones that the anterior pituitary secretes?
FSH
LH
What does FSH do?
Acts on ovary
Stimulates development of follicles
FSH + LH stimulate secretion of oestradiol and ovulation
What does LH do?
Acts on ovary
Stimulates follicle maturation, ovulation and development of the corpus luteum
FSH + LH stimulate secretion of oestradiol and ovulation
What happens in the hypothalamus when the follicular phase begins?
Hypothalamus secretes GnRH
Ant pituitary secretes FSH and a little LH
Up to 15 follicles begin to mature and form granulosa cells and theca cells
Oestrogen suppresses FSH production by the ant. pituitary (selection of dominant follicle)
What is the role of the theca cells and granulosa cells during the follicular phase?
The theca cells produce androgen which is converted by the granulosa (aromatase) to oestradiol (thickens endometrium/thins cervical mucus)
What happens in the hypothalamus once the dominant follicle has been selected?
Granulosa in the dominant follicle express LH receptor
High levels of oestrogen at mid cycle cause hypothalamus to release GnRH
Causes FSH and LH surge from ant. pituitary
What happens to the levels of LH and FSH during ovulation?
They fall
What happens to the remaining granulosa during the luteal phase?
Become part of the corpus luteum and secrete progesterone
What happens to thecal cells during the luteal phase?
Convert androgen to oestrogen
What happens 12 days into the luteal phase to oestrogen and progesterone levels?
If there is no hCG production from an embryo, the corpus luteum degenerates forming the corpus albicans
This reduces the levels of oestrogen and progesterone, starting the cycle again by removing negative feedback
At which stage of pregnancy does the corpus luteum degenerate to the corpus albicans?
6 weeks - the placenta takes over the function of secreting progesterone
