Flashcards in Gametogenesis Deck (56)
When do primordial germ cells form?
By the 2nd week of gestation
Where do primordial germ cells form?
In the yolk sac by the 2nd week
What are primordial germ cells
The cells which go on to develop into gametes
Describe the migration of primordial germ cells
From endodermal layer of the yolk sac into the embryo via the hindgut to the dorsal body wall to form the gonadal ridges
When do the gonadal ridges form?
By 6-8 weeks - they form on the dorsal body wall, stimulated by primordial germ cells deposited there
What is the role of somatic support cells in the formation of female genitalia?
They form the ovarian follicle cells
What is the role of somatic support cells in the formation of male genitalia?
They form the testis cords and eventually the Sertoli cells of the seminiferous tubules
What is the embryological origin of teratomas?
Teratomas form from primordial germ cells
When does differentiation of the primordial germ cells happen in males?
The PGCs become spermatogoonia once they reach the gonadal ridge but do not undergo meiosis until puberty
What are primordial germ cells called in females once they have been surrounded by the somatic support cells of the ovaries?
What are oogonia?
Female primordial germ cells (diploid cells)
What do oogonia become?
Primary oocytes (when they start to undergo meiosis)
What are primary oocytes?
An oogonia which has started to undergo meiosis. Meiosis is arrested in prophase 1 in diplotene phase until puberty
What do primary oocytes become?
Secondary oocytes (oocytes entering the second phase of meiosis)
When do primary oocytes mature into secondary oocytes?
When does the secondary oocyte complete meiosis?
After it the egg has been ovulated and fertilised
How many eggs are present at birth?
How many eggs are present at puberty?
How many eggs are present in a 20 week female fetus?
6-7 million (they degenerate from this point onwards
Which gene determines whether a primordial germ cell will differentiate into an egg or a sperm?
SRY gene on the Y xsome, if present the cells will turn into male gametes
What is a primordial follicle?
A female gamete surrounded by a thin layer of granulosa cells and an external basal lamina
What is a primary follicle?
A gamete surrounded by a thick layer of granulosa cells and a basal lamina
Which layer of the follicle is vascular?
The inner thecal layer
What is the Antral phase?
When the ovarian follicle forms a fluid filled cavity called the Antrum and a subset of granulosa cells surround the oocyte to form the cumulus oophorus
Which follicle cells develop FSH receptors?
The granulosa cells
Which follicle cells develop LH receptors?
Which follicle cells produce testosterone and progesterone?
Thecal cells in response to LH
Which follicle cells produce estradiol?
Granulosa cells under the influence of FSH by converting testosterone from thecal cells to estradiol with aromatase enzyme
When are follicles dependent on hormones for development?
Once the Antrum forms