Cyclic Activity of the Ovaries

1. Cyclic Activity of the Ovaries
Joanne Shoesmith – N0604416 | Nottingham Trent University - Clifton Campus | Biomedical Science – Human Systems
What is the Ovarian Cycle?
Follicular Phase
Ovulation Phase
Luteal Phase
Hormone Activity During Ovarian Cycle
Conclusion
During the 28 cycle it is important to remember that there are two main cycles. The ovarian
cycle and the menstrual cycle. Both cycles are regulated by the hypothalamo-pituitary-ovarian
axis. Saladin (2015).
The hypothalamus regulates the pituitary gland itself, while the pituitary hormones regulate
the ovaries.
The ovaries secrete hormones that regulated the uterus.
It is also important to note here that the ovaries have a positive and negative feedback on the
pituitary and hypothalamus. This is known as the feedback loop.
The negative feedback occurs during the follicular phase when FSH stimulates follicle growth,
this also stimulates the granulosa cells to secrete estradiol. In response to this the estradiol
helps to regulate the follicular receptors for FSH and LH and also the estradiol. As the estradiol
is secreted it inhibits the secretion of GnRH. The pituitary gland secretes less FSH but
increases the amount of LH secreted. Follicles that needed the FSH to continue their process
of growing now start to degenerate (atresia). The dominant follicle with the most FSH receptors
and adequate blood supply can now mature.
• Low levels of E2 and P cause negative feedback to inhibit FSH and LH secretion
• High levels of E2 and P stimulate FSH and LH secretion
References
(Fig. 1) University of Oklahoma Health Services Centre (no date) Primary Follicle [online]. Available at:
https://instruction.cvhs.okstate.edu/histology/fr/PrimaryFollicle.htm [Accessed 19 February 2015].
(Fig. 2) University of Oklahoma Health Services Centre (no date) Ovary [online]. Available at:
http://www.ouhsc.edu/histology/Glass%20slides/83_13.jpg [Accessed 19 February 2015].
(Fig. 3) University of Oklahoma Health Services Centre (no date) Female Reproductive System [online]. Available at:
http://www.ouhsc.edu/histology/Text%20Sections/Female%20Reprodcutive.html [Accessed 02 March 2015].
(Fig. 4) University of Oklahoma Health Services Centre (no date) Ovary [online]. Available at:
http://www.ouhsc.edu/histology/Glass%20slides/83_12.jpg [Accessed 19 February 2015].
(Fig. 5) Advanced fertility.com (1996) Pictures of immature and mature IVF eggs [online]. Available at:
http://www.advancedfertility.com/immature-ivf-eggs.htm [Accessed 02 March 2015].
(Fig. 6) Conceiveeasy.com (2000) Ways to increase fertility with only one fallopian tube [online]. Available at.
http://www.conceiveeasy.com/get-pregnant/one-fallopian-tube/ [Accessed 02 March 2015].
(Fig. 8) and 9 IFL Science.com (20214) Direct Brain-to-Brain Communication used in Humans [online]. Available at:
http://www.iflscience.com/brain/direct-brain-brain-communication-used-humans [Accessed 02 March 2015].
Saladin, K. (2015) The Sexual Cycle. 7th ed. New York: McGraw-Hill Education.
Saladin, K. (2015) The Ovarian Cycle. New York: McGraw-Hill Education.
Stage 1. See Fig. 1 – Formation of the primary follicles. Primordial follicles are activated by the
stimulation of FHS, released by the anterior pituitary gland in small amounts, helping with the
development of the follicles into primary follicles.
The follicular cells begin to increase in size and duplicate themselves, creating layers of around the
oocyte, known as granulosa cells. See Fig. 2
The granulosa cells develop around the oocyte and integrate their microvilli with those of the oocyte,
enabling the crossover of materials to the growing oocyte. See Fig. 3.
The ever increasing size of the oocyte is due to stimulation of the hormone FSH.
A thecal cell layer around the follicle works in unison with the granulosa cells which are increasing and
multiplying. Working in conjunction with each other to produce the female sex hormone estrogen.
Still in the follicular phase of the cycle the primary oocyte is still continuing to increase in size. During
this stage in the phase there is an increase in follicular fluid (liquor folliculi), See Fig. 4, secreted through
the cell walls. The follicle is now larger and increasing at a fast pace.
Now known as Graafian, or most commonly know as the tertiary follicle at a size of approximately
15mm, (Frederich Martini, 1995, pg 1080) formed from the secondary follicle of which there is only one
in the ovary that will develop further.
The physicality of the structure projects through the ovarian capsule, bulging through its surface. This is
where the oocyte surrounded by the granulosa cells is suspended in prophase of the first meiotic
division and projects towards the central chamber of the bulge in the surface of the ovary.
(Saladin,2015, p.1074) refers to this as “a nipplelike stigma”
LH levels rise and this completes the growing and development of the oocyte.
Meiotic division produces a second oocyte along with a polar body, see Fig. 5 and enters the second
meiosis stage. Meiosis 2 will not complete unless fertilised.
Fig. 2 Granular cells surround the oocyte
Fig. 3 Granulosa cells developing around
the oocyte
Fig. 5 Second Oocyte and Polar body
Fig. 6 fimbriae of the fallopian tube
Estradiol Progesterone LH FSH
OvulationFollicular Phase
Day 1 - 10
Luteal Phase
Day 16 - 28
Ovary
Body Temperature
0.5⁰c
A secondary oocyte is released from the tertiary follicle as it nears ovulation phase.
Together the oocyte and its granulosa cells no longer stay attached to the follicular wall and float within
the antrum. This usually occurs on day 14 of the cycle.
Granulosa cells now known as Carona Radiata along with the oocyte are released as the follicular wall
ruptures into the pelvic cavity.
fimbriae transfer the oocyte to the uterine tube. See Fig. 6.
Fig. 1 Primary Follicle
Fig. 4 Follicular Fluid
Fig. 7
Fig. 4 shows the release of hormones into the body during the ovarian cycle. Fig 4 also
shows the change in the body’s basal temperature. This is cause by an effect of
progesterone.
Day 10 - 16
The tertiary follicle folds in on itself and collapses.
Ruptured blood vessels release blood into the atrial chamber and any granulosa cells spread across the
area creating a structure known as the corpus luteum. The hormone LH is responsible for the activity in
this stage of the cycle.
Progesterone, a steroid hormone is produced by the lipids contained in the corpus luteum and prepares
the uterus for pregnancy by stimulating the uterine lining to grow and also the stimulation of the uterine
gland.
When pregnancy ids absent degeneration of the corpus luteum takes place, around 12 days after
ovulation, after which hormone levels of estrogen and progesterone fall rapidly.
Scar tissue known as corpus albican is formed by fibroblasts in the corpus luteum. This is now the end
of the cycle.
Follicle Stimulating
Hormone: Secreted
from the anterior
pituitary in the brain
after stimulation from
GnRH which has been
released from the
hypothalamus.
Stimulates growth of
the follicles.
Luteinising Hormone:
Also secreted from the
anterior pituitary in the
same way as FSH.
Secreted by the
growing follicle. Low
levels inhibit the
secretion of pituitary
gonadotropins by
causing hypothalamus
to increase levels of
GnRH. Sensitivity of
GnRH LH-releasing
cells also increases,
ultimately increasing
LH levels.
Secreted by the
corpus luteum after
continuous to be
stimulated by LH. This
has a negative
feedback which
reduces the secretion
of LH and FSH which
stops another egg
from being released.
The activities of the ovarian cycle can be broken down into three well known
phases and all are regulated by four main hormones.
FSH LH Estradiol Progesterone
Hormones of the Anterior Pituitary and
Ovaries