Gametogenesis Flashcards
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?
Oogonia
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?
At puberty
When does the secondary oocyte complete meiosis?
After it the egg has been ovulated and fertilised
How many eggs are present at birth?
1-2 million
How many eggs are present at puberty?
300,000
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?
Thecal cells
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
What is a secondary follicle?
An egg surrounded by a zona pellucida, granulosa cells, thecal cells
What is a tertiary follicle?
A follicle surrounded by a zona pellucida, a cumulus oophorus, an antrum, a layer of granulosa cells, a basal lamina and two layers of thecal cells (internal and external)
Which follicle cell contains aromatase enzymes?
Granulosa cells for conveying testosterone to estradiol
What does aromatase enzyme do?
Converts testosterone to estradiol in the granulosa cells
When does the embryo become a fetus?
Week 8
When does the female have the most eggs?
At 20 weeks (approximately 7 million)
Where do the spermatogoonia live?
In the seminiferous tubules, undergoing mitotic divisions, they do not undergo meiosis until puberty
What phase do primary oocytes stay until puberty?
diplotene phase of prophase 1
What arrests maturation of the primary oocytes?
Occyte maturation inhibitor (which is secreted by the follicle cells)
What is the difference between theca interna and externa?
Theca interna is vascular
Theca externa is fibrous and secretory
Where and when does fertilisation occur?
Ampulla of the fallopian tube at 24-48 hours after ovulation
What is capacitation?
A change that occurs to the spermatozoa in the vagina and uterus which causes the acrosomal head to destabilise and the tail to become more mobile. Calcium fluxes into the cell allowing greater energy and mobility
What enzyme is released on the sperm penetrating the corona radiata?
Hyluronidase
What happens when a sperm reaches the zona pellucida?
It releases enzymes from the acrosomal head and a zona reaction occurs preventing other sperms to penetrate. Also the secondary oocyte completes meiosis
Describe the maturation phase of the egg that is released at ovulation?
secondary oocyte arrested in metaphase II
Surrounded by a zona pellucida and corona radiata
An oogonium has how many chromosomes and how many chromatids?
46 chromosomes
46 chromatids
A primary oocyte has how many chromosomes and chormatids?
46 chromosomes
92 Chromatids
A secondary oocyte has how many chromosomes and chormatids?
23 chromosomes
46 chromatids
An ovum has how many chromosomes and chormatids?
23 chromosomes and 23 chromatids
What does ootidogenesis refer to?
Primary oocyte undergoing meiosis 1 and 2 to become an ootid
What does oocytogenesis refer to?
An oogonium growing and maturing into a primary oocyte
What does spermatocytogenesis refer to?
Maturation of a spermatogonium to a primary spermatocyte
What is the maturation of a spermatogonium to a primary spermatocyte called?
Spermatocytogenesis
What does spermatidogenesis refer to?
Spermatocytes undergoing two meiotic divisions to become spermatids
What does a spermatocyte become?
A spermatid
What does spermiogenesis refer to?
The development of spermatozoa from spermatids
What is the process of creating spermatozoa from spermatids?
Spermiogenesis
