Lecture 4 - Ovarian Function Flashcards
At what stage of development do the primordial germ cells migrate and where do they migrate to?
They migrate in weeks 3-7 and they migrate to the genital ridges. This is by chemotaxis
What must be absent for the female gonads to form?
SRY gene
How do the primordial follicles form? what cells do they contain?
The sex cord cells cluster around the primordial germ cells but do not penetrate deeply. This forms the primordial follicles that contain the granulosa cells.
Why does normal oocyte development not occur in turners syndrome?
Both X chromosomes must be present for normal oocyte development. Normal overy development also requires normal germ cells.
What are the 5 stages of development of the oocyte?
Primordial germ cells Oogonium Primary oocyte Secondary oocyte Mature oocyte
Which stages of oocyte development do meiosis occur?
Primary oocyte undergoes meiosis to secondary oocyte
Secondary oocyte undergoes meiosis to form mature oocyte.
When do the two steps of meiosis occur in females and what is this controlled by?
Meiosis one occurs when the female is in utero which means she is born without any primordial germ cells.
Meiosis two occurs at fertilisation so there can be a very long period between meiosis 1 and 2.
In males the first and second meiosis give rise to 4 sperm cells, what happens for females?
The two meiosis divisions result in only one oocyte being produced and two polar bodies.
How can polar bodies help determine if fertilisation has occured?
There will be a polar body present from the second meiotic division if fertilisation has occured.
What are the equivalent of sertoli and leydig cells for females?
Sertoli cells are granulosa cells
Leydig cells are theca cells
How long does it take from the inital development of a primordial follicle to ovulation?
375 days approx.
What is the structure of the primordial follicle and what occurs in this stage?
It is the oocyte surrounded by a single layer of flattened granulosa cells.
Oocyte begins to grow
How often do primordial follicles form?
They form every few days after puberty and are independent of the menstrual cycle.
What is the structure of the primary follicle?
Granulosa cells become more cuboidal and theca cells and zona pellucida bein to become visible.
What is the structure of the secondary follicle?
Granulosa proliferate, theca cells divide into two layers, interna and externa
What is the structure of the mature follicle?
Granulosa cells secrete follicular fluid and the oocyte is surrounded by a corona radiata.
How are follicles often divided into two catagories?
Pre-antral and post-antral
What is the role of oestrogens?
They cause follicle maturation and prepare the endometrium for pregnancy.
Thin the cerical mucus
Help development of secondary sexual characteristics
What is the role of progesterone?
It is produced by the corpus luteum post ovulation. It maintains the lining of the uterus thoughout pregnancy.
What is the two cell hypothesis for the production of oestrogen?
That testosterone is produced by the theca cells which moves to the granulosa cells where it is converted to oestrogen by aromatase.
What effects do FSH and LH have on the theca and granulosa cells?
FSH causes increased aromatase activity in granulosa cells
LH causes increased cholestrol uptake by theca cells
What are the three phases of the medstrual cycle?
Follicular phase
Ovulation
Luteal phase
What happens in the follicular phase?
GnRH cause secretion of FSH from the pituitary. This causes development of granulosa and theca cells into follicles. This causes production of oestrogen that causes an LH spike from the pituitary just before ovulation.
What happens in the ovulation phase?
The oocyte enters meiosis 2 and arrests at the metaphase.
Ovulation
What happens in the luteal phase?
Corpus luteum forms
Granulosa cells produce oestrogen and progesterone
Negative feedback from progesterone causes FSH and LH to fall.
How does luteolysis occur?
after around 12 days if there is no hCG from an embryo then the corpus luteum begins to degrade.
