Ovary of a three month calf
Keywords: ovary, bovine, AMH, primary, primordial, follicle,
puberty
Image size: 466 x 351px
A cross sections of the ovary of a three month old heifer calf showing primary follicles (a single layer of luteal cells) and secondary follicles (multiple layers of luteal cells). Note the primordial follicles containing primary oocytes. These 2n oocytes are suspended in prophase, prior to the reduction division of meiosis. Reduction to the haploid state will only occur when a selected follicle is stimulated by LH prior to ovulation.
A cross sections of the ovary of a three month old heifer calf showing primary follicles (a single layer of luteal cells) and secondary follicles (multiple layers of luteal cells). Note the primordial follicles containing primary oocytes. These 2n oocytes are suspended in prophase, prior to the reduction division of meiosis. Reduction to the haploid state will only occur when a selected follicle is stimulated by LH prior to ovulation.
Primordial follicles are those that have flat epithelium
surrounding the basement membrane of the oocyte. When these become more cuboidal
as perhaps those are here, the follicle is termed primary instead of primordial.
When the granulosa (g) cells, which are all inside the basement membrane (seen
best on a high power image, where it is as labeled “bm”) multiple but have not yet formed an antrum, the follicle is termed a secondary follicle. A secondary follicle is shown below.
Image size: 466 x 351px
Those with a well formed antrum are tertiary follicle; there are none in this image because they only form at the approach of puberty. Outside of the basement membrane, cells from the stroma (s) accumulate and form the theca of the follicle. These follicles are too young to show the theca but it is obvious in tertiary follicles. The theca externa is fibrous in nature but he theca interna is glandular, producing androgens which are aromatized to estrogens by the granulosa cells.
Those with a well formed antrum are tertiary follicle; there are none in this image because they only form at the approach of puberty. Outside of the basement membrane, cells from the stroma (s) accumulate and form the theca of the follicle. These follicles are too young to show the theca but it is obvious in tertiary follicles. The theca externa is fibrous in nature but he theca interna is glandular, producing androgens which are aromatized to estrogens by the granulosa cells.
The zona pellucida is already present in primary follicles
but is best seen here in a secondary follicle on a high power image, where it
is as labeled “zp”
Pre antral follicles like these form anti-müllerian hormone
(AMH) which prevents them from binding FSH and being recruited prematurely and
en mass. AMH measurements are valuable as an indicator of the number of these
pre-antral follicles and hence, the potential value of the heifer as an embryo
donor.
