Gametogenesis and Assisted Reproductive Technologies Flashcards
What is spermatogenesis?
Spermatogenesis is the production of mature sperm - spermatazoa from spermatogonia (from PGCs)
Where does spermatogenesis take place?
In the seminiferous tubules of the mature testes. The differentiation occurs in the walls of the tube and the mature sperm released in to the lumen and stored in epididymis
How do PGCs turn into spermatogonia?
During the development of the testes, PGCs become spermatogonia, which act as unipotent cells to form spermatozoa
Which cells support the development of mature sperm cells and how do they do this?
In the seminiferous tubules of the testes, there are Sertoli cells which give nutritional support and an appropriate hormonal environment to support the differentiation of spermatazoa by being in close proximity to the spermatogonium
Explain the cell types and processes involved in spermatogenesis
PGCs give rise to spermatogonia, which undergo mitosis (maintaining the pool) and differentiate to form a primary spermatocyte, which undergoes meiosis I to form secondary spermatocytes (44XY) which undergo meiosis II to become spermatids (22X/Y) which undergo two stages of differentiation to become spermatozoa
Describe the hormonal axis involved in sperm production
GnRH is released by the hypothalamic-pituitary axis which stimulates the release of LH and FSH from anterior pituitary. LH stimulates Leydig cells to release testosterone that synergises with FSH to stimulate the Sertoli cells to optimise spermatogenesis
Describe the development of the oogonium
During the devleopment of the ovaries, PGCs tunr into oogonia. The oogonium (ovum stem cell) develops into a primary oocyte (diploid) in pre pubescent years. The primary oocyte is frozen in prophase I of meiosis. By the time the antral follicle ruptures, the primary oocyte completes meiosis (haploid) becoming a secondary oocyte. A polar body is expelled. This becomes frozen in metaphase II and only completes meisosis after fertilisation.
Describe the development of the follicle in oogenesis
Oogonium form primordial follicles in pre pubescent years. At puberty, the primordial follicles become primary follicles, which grow, producing a growing follicle, that results in the production of follicular fluid (hyaluronic acid) inside the follicle. The pools join together becoming an antrum (lake of fluid), and the antral follicle bursts, releasing the secondary oocyte. The antral follicle becomes the corpus luteum which stays for about a week before degrading
Describe the role of FSH and LH in oogenesis.
Both produced by anterior pituitary in response to GnRH produced by hypothalamus. FSH stimulates the follicle to proliferate, and to produce estrogen, via the production of androgens from cholesterol stimulated by LH, and FSH stimulates conversion of androgens to estrogen. FSH also causes production of follicular fluid
What is the role of Estrogen in oogenesis?
Estrogen goes into bloodstream and go to hypothalamus and anterior pituitary, exerting negative feedback, lowering GnRH levels and inhibits pituitary producing FSH and LH. LH starts to rise again, and switches to a positive feedback mechanism, resulting in an LH surge,which brings about the rupturing of the antral follicle
Why doesn’t FSH not increase during the LH surge?
Because the Graffian follicle releases Inhibin B which inhibits the release of FSH, so FSH levels stay low during the LH surge
How does LH rupture the Graffian follicle?
Increases blood flow and permeability to the follicle, increasing follicular fluid production. Also stimulates proteases to cause rupture of the follicle, releasing the secondary oocyte - ovulation
What is the role of LH in regards to the corpus luteum?
LH also stimulates the corpus hemorrhagicum (follicle full of blood) to differentiate and become corpus luteum (accumulation of lipids, cholesterol, fat)
What is the role of the corpus luteum?
Corpeus luteum, stimulated by LH to produce progesterone.
Describe what occurs after ovulation
The secondary oocyte moves into the fallopian tubes via local currents produced by the fallopian tube clawing, and is moved by the cilia into the correct location where it waits until fertilisation. If not fertilised in about 12-24 hours it begins to break down