Beginnings, Growth and Development
© Dr Mark Hill (2010)
Laboratory 3 - Oogenesis and Ovulation
New Site BGD
This page covers gametogenesis within the ovary. With the help of the tutors and other students you will work your way through identifying features described in the text.
Begin by looking at the ovary and the formation of the follicle containing the egg which matures and is released
upon ovulation. The images are arranged in series so that progressive stages of the maturing follicle can be seen. The final image on this current page is a link to a movie showing follicle development and ovulation. Use the series of images of the cat ovary below to identify the key features described in the associated text.
Note: This should be a revision of the Ovary Histology Practical you have already completed. If you have trouble with
the terms, there is a glossary at the bottom of each page.
The graph below shows the changes in human germ cell numbers in the ovary with age, peaking at about 7 million (occuring in early fetal development)
and then decreasing by apopotic cell death. At puberty there remain only about 400,000 and only about 10% of these will be released through reproductive life.
(More? Human Menstrual Cycle)
(Based on data from: Hassold, etal., Environ Mol Mutagen 1996. 28: 167-175)
Ovary (cat, cross-section) showing histology and maturation of follicle.
Image (low magnification) showing cortical primordial follicles with primary (preantral) and
secondary (antral) follicles lying deeper. Mesovarium at lower right and blood vessels in medullary region.
At this magnification, the overall organization of the ovary can be observed, cortex/medulla organization and arrangement of the
maternal blood vessels, but few specific follicle details can be seen.
The next image is of the ovarian cortical region.
Ovary Cortex (low power)
Ovary cortex showing primordial follicles.
At the top of the image, is the outside of the ovary.
The thick connective tissue outer layer is the tunica albuginea. Over which a single layer of cells called
the germinal epithelium (not visible) cover the surface of the ovary.
The next layer contains the earliest primordial follicles, single cells with pale cytoplasm and darkly stained nuclei.
The next layer contains many growing follicles at various stages of maturity and development.
There is also evidence of degeneration as atretic follicles.
At the bottom of the image, is the medullary region of the ovary. Note the large number of maternal blood vessels which are the circulatory conduits
for the estrogens and progesterones produced by the theca surrounding the ovarian follicles.
Note: germinal epithelium, tunica
albuginea, primordial and atretic follicles. Note larger preantral follicle with (from the centre
out) nucleus of maturing oocyte, oocyte cytoplasm, zona pellucida (pink ring), follicle cells, stromal cells.
Ovary Cortex Primordial Follicles
View of cortical ovary region showing primordial follicles and a single preantral follicle, with atretic follicle to its left.
Bottom of picture shows outer cells of antral follicle.
Ovary Cortex (High Power)
High power view of ovary cortical region showing primordial follicles and a single preantral follicle.
Features: germinal epithelium, tunica albuginea, preantral follicle, nucleus of oocyte, oocyte cytoplasm, zona pellucida,
Call-Exner body, stratum granulosa, basement membrane, theca, blood vessels surrounding follicle in theca layer.
Ovary Cortex and Medulla (Low Power)
Low power view of ovary cortex and medullary region. Note 3 stages of follocle development (primordial, preantral and antral).
- cortical primordial follicles
- follicular cells
- stromal cells
- preantral follicle- zona pellucida, stratum granulosa, theca
- early preovulatory follicle (Graafian)- oocyte, zona pellucida, corona radiata, cumulus oophorus, liquor folliculi, stratum granulosa, theca interna, theca externa, blood vessels surrounding
follicle (Graafian Follicle named after Regnier de Graaf (1641-1673), a Dutch physician study of pregnancy in rabbits)
Movie (click image to play) showing process
of ovulation (release of oocyte and follicular
fluid). Click on movie to start.
Note that following ovulation the remnant of the follicle
will degenerate if implantation does not occur (non-pregnant) forming a corpus albicans or following
implantation (pregnancy) a corpus luteum which
provides endocrine support to the uterus.
An endocrine signal (hCG human Chorionic Gonadotropin) from the implanting conceptus syncitiotrophoblasts maintains the corpus luteum,
which in turn supports the uterine functional lining, preventing menstruation.
(Note Movie requires Quicktime
to be installed on your computer)
Link to next page in this Practical 3 - Gametes
- antrum - (L. a cave), cavity; a
nearly-closed cavity or bulge. In the ovary this
refers to the follicular fluid-filled space
within the follicle.
- atretic follicle - An ovarian follicle
that fails to mature and degenerates. Also
called "atresia" refering to the process of
degeneration of the ovarian follicle.
- corona radiata - Layer of follicle
cells of cumulus oophorus remaining attached to
zona pellucida of oocyte after ovulation. Also
called granulosa cells.
- corpus albicans - (L. corpus = body, L. albicans = whitish); a degenerating corpus luteum in ovary.
- corpus luteum - (L. corpus = body, L. luteum = yellow) The remains of ovarian follicle
after ovulation that acts as an endocrine organ supporting pregnancy and preventing menstruation
(loss of the endometrial lining). de Graaf first observed it in the ovary of a cow as a yellow structure.
- cortical - (L. Corticalis) at the outside (like the bark of a tree), usually combined with medulla meaning the core.
- cumulus oophorus - (L. cumulus = a little mound G. oon = egg + phorus = bearing);
part of the wall of an ovarian follicle surrounding and carrying the ovum (oocyte).
- follicle - (L. folliculus = little
bag,dim. of L. follis). A structure which
develops in the ovary and contains a developing
- follicular fluid - (or follicular
fluid) the fluid found in the antrum of a
secondary follicle. Secreted by cells in the
wall of the follicle. This fluid is released
along with the oocyte at ovulation.
- germinal epithelium - cellular
component covering surface of ovary, it is
continuous with mesothelium covering mesovarium.
Note that it is a historical misnomer, as it is
not the actual site of germ cell formation.
- granulosa cells-
- Mesovarium - mesentry of the ovary
formed from a fold of the broad ligament that
attaches the ovary
- medullary - (from L. medius = in the
middle) relating to the medulla; pith, marrow,
inner portion of an organ. Usually combined with
cortex (cortical) meaning the outer layer.
- ovulation - release of the oocyte from
the mature follicle. In humans generally a
single oocyte is released from a cohort of
several maturing follicles.
- primordial follicle - Present in the ovary from birth, located in the stroma of the
ovary cortex beneath the tunica albuginea. The primordial follicle is the oocyte and the surrounding follicular cells.
- primordial germ cell - oocyte present
in the primordial follicle ovary from birth,
located in the stroma of the ovary cortex
beneath the tunica albuginea. The primordial
follicle is the oocyte and the surrounding
- secondary (antral) follicles -
- stromal cells - in the ovary, cells
surrounding the developing follicle that form a
connective tissue sheath (theca folliculi). This
layer then differentiates into 2 layers (theca
interna, theca externa). This region is
vascularized and involved in hormone secretion.
- theca folliculi - stromal cells in the
ovary, cells surrounding the developing follicle
that form a connective tissue sheath. This layer
then differentiates into 2 layers (theca
interna, theca externa). This region is
vascularized and involved in hormone
- theca externa - stromal cells forming
the outer layer of the theca folliculi
surrounding the developing follicle. Consisting
of connective tissue cells, smooth muscle and
- theca interna - stromal cells forming
the inner layer of the theca folliculi
surrounding the developing follicle. This
vascularized layer of cells respond to LH
(leutenizing hormone) synthesizing and secreting
androgens which are processed into
- tunica albuginea - dense connective
tissue layer lying between germinal epithelium
and cortical region of ovary.
- uterus - site of embryo implantation
and development. Uterine wall has 3 layers;
endometrium, myometrium, and perimetrium.
- zona pellucida - extracellular layer
lying directly around the oocyte underneath
follicular cells. Consists of glcosaminoglycans
and glycoproteins (ZP1, ZP2, ZP3).
There are several different nomenclatures for
the stages of follicle maturation.
- primordial follicle
- small follicle
- type 1, 2, 3 (25cells)
- primary follicle
- preantral follicle
- type 4 (26-100 cells), type 5 (101-300 cells)
- secondary follicle
- small and large antral follicle
- type 6 (3001-500 cells), type 7 (501-1000
- preovulatory follicle
- Graafian follicle
- type 8 (>1000 cells)
At any one time the majority of follicles are
destined not to complete maturation and at any
stage (from type 4-7) degeneration of the follicle
can occur. This process is called ATRESIA.
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