Let’s revise the ovarian cycle today ^__^
PS: Since tumblr does not allow me to upload more than 10 photos, you’ll have to follow the numbers as you read.. However, I recommend you read the post from the site itself since that will be more convenient and easy for you to read :)
Click here to read the comic from the site
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On the first day of menstruation, follicular stimulating hormone (FSH) is secreted from the pituitary gland.
FSH stimulates the growth of immature ovarian follicles in the ovary.
Comic strip 1:
Let me present to you, which cell secretes what - A comic by Medicowesome =D
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The follicle that reaches maturity is called a Graafian follicle (tertiary follicle).
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Will Oocyte become an embryo? *mysterious music plays in the background* =P
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Because stories on helpful loyal friends are heart melting <3
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LH acts on theca cells to induce androgen production.
Androgen substrate required for ovarian estrogen biosynthesis.
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FSH stimulates granulosa cells to convert androgens (coming from the thecal cells) to estradiol.
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Granulosa cells have an enzyme, aromatase, which aids the conversion of androgens to estradiol.
Estradiol is necessary to maintain oocytes in the ovary.
Also, during the follicular phase, estradiol suppresses production of LH from the pituitary.
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When the oocyte has nearly matured, levels of estradiol reach a threshold above which the suppressive effect of estrogen on the pitutary is reversed.
Estrogen stimulates the production of a large amount of LH, this process is known as the LH surge.
LH surge is necessary for ovulation.
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The surge in luteinizing hormone increases cAMP in the theca externa cells.
This increases progesterone and PGF2a production.
PGF2a induces the contraction of the smooth muscle cells of the theca externa.
Contraction increases intrafollicular pressure, which aids in rupture of the mature oocyte.
The mature follicle also secretes collagenase.
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The rupture of follicle and the ovary’s wall allows the oocyte to escape.
It is caught by the fimbriated end and travels to the ampulla of the fallopian tube.
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After rupture of the mature ovarian follicle, the theca interna cells & granulosa cells differentiate into the corpus luteum.
Theca lutein (small luteal cells) secrete androgens and progesterone.
Granulosa lutein cells produce progesterone.
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The corpus luteum produces a relatively high levels of progesterone and moderate levels of estradiol and inhibin A.
Progesterone is responsible for the decidualization of the endometrium (its development) and maintenance.
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LH is required for the maintenance of corpus luteum.
The progesterone produced by the corpus luteum induces the adrenals to produce estrogen.
Estrogen and progesterone suppress the production of the FSH and LH that are needed to maintain the corpus lutem.
Consequently, the level of FSH and LH fall quickly over time, and the corpus luteum subsequently atrophies.
The atrophied corpus luteum is called corpus albicans.
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Falling levels of progesterone trigger menstruation and the beginning of the next cycle.
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The loss of the corpus luteum is prevented by fertilization of the egg.
The embryo produces human chorionic gonadotropin (hCG).
hCG is very similar to LH and it preserves the corpus luteum.
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The corpus luteum produces progesterone until the placenta begins to take over progesterone production around ten weeks gestation.