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Folliculogenesis

Again, ovarian follicles are oocytes and their supporting cells. They grow and develop in a process called folliculogenesis    , which typically leads to ovulation of one follicle approximately every 28 days, along with death to multiple other follicles. The death of ovarian follicles is called atresia, and can occur at any point during follicular development. Recall that, a female infant at birth will have one to two million oocytes within her ovarian follicles, and that this number declines throughout life until menopause, when no follicles remain. As you’ll see next, follicles progress from primordial, to primary, to secondary and tertiary stages prior to ovulation—with the oocyte inside the follicle remaining as a primary oocyte until right before ovulation.

Folliculogenesis begins with follicles in a resting state. These small primordial follicles    are present in newborn females and are the prevailing follicle type in the adult ovary ( [link] ). Primordial follicles have only a single flat layer of support cells, called granulosa cells    , that surround the oocyte, and they can stay in this resting state for years—some until right before menopause.

After puberty, a few primordial follicles will respond to a recruitment signal each day, and will join a pool of immature growing follicles called primary follicles    . Primary follicles start with a single layer of granulosa cells, but the granulosa cells then become active and transition from a flat or squamous shape to a rounded, cuboidal shape as they increase in size and proliferate. As the granulosa cells divide, the follicles—now called secondary follicles    (see [link] )—increase in diameter, adding a new outer layer of connective tissue, blood vessels, and theca cells    —cells that work with the granulosa cells to produce estrogens.

Within the growing secondary follicle, the primary oocyte now secretes a thin acellular membrane called the zona pellucida that will play a critical role in fertilization. A thick fluid, called follicular fluid, that has formed between the granulosa cells also begins to collect into one large pool, or antrum    . Follicles in which the antrum has become large and fully formed are considered tertiary follicles    (or antral follicles). Several follicles reach the tertiary stage at the same time, and most of these will undergo atresia. The one that does not die will continue to grow and develop until ovulation, when it will expel its secondary oocyte surrounded by several layers of granulosa cells from the ovary. Keep in mind that most follicles don’t make it to this point. In fact, roughly 99 percent of the follicles in the ovary will undergo atresia, which can occur at any stage of folliculogenesis.

Folliculogenesis

This multipart figure shows how follicles are generated. The top panel shows the six stages of folliculogenesis. In each stage, the major cell types are labeled. The bottom part shows a micrograph of a secondary follicle and the major parts are labeled.
(a) The maturation of a follicle is shown in a clockwise direction proceeding from the primordial follicles. FSH stimulates the growth of a tertiary follicle, and LH stimulates the production of estrogen by granulosa and theca cells. Once the follicle is mature, it ruptures and releases the oocyte. Cells remaining in the follicle then develop into the corpus luteum. (b) In this electron micrograph of a secondary follicle, the oocyte, theca cells (thecae folliculi), and developing antrum are clearly visible. EM × 1100. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

Questions & Answers

structure of a serous membrane
Ziyanda Reply
are you asking?
Isa
yes
MOHD
In anatomy, serous membrane (or serosa) is a smooth tissue membrane consisting of two layers of mesothelium, which secrete serous fluid. The inner layer that covers organs (viscera) in body cavities is called the visceral membrane. A second layer of epithelial cells of the serous membrane, called th
Isa
The two layers of serous membranes are named parietal and visceral. Between the two layers is a thin fluid filled space.[2] The fluid is produced by the serous membranes and stays between the two layers to reduce friction between the walls of the cavities and the internal organs when they move with
Isa
a continuation from the 1st one:: A second layer of epithelial cells of the serous membrane, called the parietal layer, lines the body wall. Between the two layers is a potential space, mostly empty except for a few milliliters of lubricating serous fluid that is secreted by the two serous membranes
Isa
Name the two phases of metabolism
Grace Reply
reproduction and growth
Zozo
how about anabolism and catabolism?
Japhar
In Simply Anabolism means formation... Catabolism means breakdown
Jazil
two phases of reproductio?
Japhar
Anabolism indicates potential & catabolism potential converts to kinetic
Doctor
Name the most important life process in the human body in terms of anatomy and physiology
Grace
Nervous system
Nimco
Every system is important for body functions
Jazil
what is the difference between the functions of the adhesion belt and the desmosomes?
Mason Reply
what are the derivatives of the germ layer?
Miriam Reply
zygote
Zozo
Pls explain the atlas of the cervical vertebral column
Ifunanya Reply
why does the material not allow in mri
Simran Reply
what do you mean 'mri'
Nimco
short for magnetic resonance imaging. "the researchers used MRI to record the brain activity" a medical examination performed using magnetic resonance imaging. "he's having an MRI to determine the extent of the injury" an image obtained by magnetic resonance imaging. "after looking at the MRI, the d
Riyaz
what is the meaning of sutures
Ibrahim Reply
i do not know
Nimo
immovable joints btn two bones.eg the skull bones
Japhar
Really,it's true
Nimco
Sutures are immovable junction between two bones e.g those of the skull
Surphy
what should I do to get or to know what to do for me to be excellent in the course of anatomy and physiology
Sandra Reply
study harder
Japhar
Between the heart and the Brain which one is more important to human being... discuss
Faith Reply
well the brain is important for motor skills, the heart is important for involuntary muscle movement supporting body functions. the body can survive without brain involvement, but the body cannot last without the heart
john
granted the heart is important, but the brain gives the body purpose
john
the brain is more important
Kevin
why?
john
brain
tracey
Even though the brain helps the human being to behave normally and purposefully, I think the heart is much more important cos human being cannot live without the heart
Dzifa
why?
john
change the question
Bind
hello guys
Kevin
heart
Kevin
it is difficult to select which organ is more important, now you can replace the heart with a mechanical device and the body could still function, and with technology today brain activity can also be replicated. But life would not be the same
john
there's coordination btn the two..so without any of them no life
Japhar
the heart
The brain is important to humans.
Zozo
what is homeostasis
Rebecca Reply
It is the condition when body feel comfortable
Jazil
Wo feels hungry, thirty due to homeostasis
Jazil
Is the maintenance of the internal environment of all the body cells for normal growth
Komolika
what is the composition of saliva
Vijay Reply
ഫസ്റ്റ് ചാപ്റ്റർ ഇംപോർട്ടൻസ് പോസ്റ്റ്
Reshma Reply
Yes....
Loving
nhi samjh aya
Anshika
Nhi wt is this
Loving
I don't know
Anshika
Okk wre frm u r
Loving
what is mean of? reshma
Asad
I don't know but would like to
Rebecca
D bone in d ankle joint re what ?
Ifunanya Reply
patellar
Ibrahim
I thought that patella us the bone found in the knee cap
Ifunanya
fib and tib join with tarsal form ankle joint
Ava
Thanks
Ifunanya
can one define a cell as a basic unit of a living organism
Michael Reply
cell is the structural and functional unit of living organisms
Fidel
Which of the following hormones are responsible for the adolescent growth spurt? estrogen and testosterone, even in women?
Kepa Reply
estrogen
Farhana
Estrogen!
Jazil
estrogen hormone
Michael
yes estrogen hormone
Anshika
yes
Sale
testrogen
Rebecca

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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