Female Reproductive System
The female reproductive system consists of the paired ovaries and oviducts (or uterine tubes), the uterus, the
vagina, and the external genitalia
Beginning at menarche, when the first menses occurs, the reproductive system undergoes monthly changes in
structure and function that are controlled by neurohormonal mechanisms
Ovaries:
o Each ovary is covered with simple cuboidal epithelium
This overlies that tunica albuginea
o Its cortex has many ovarian follicles
o The internal medulla contains loose connective tissue and blood vessels entering the organ through the hilum.
Early development of the ovary:
o Primordial germ cells migrate from the yolk sac to the gonadal primordial where they divide and differentiate as
oogonia.
o Primary oocytes are arrested at prophase of meiosis and are surrounded by follicular cells to form an ovarian
follicle.
o By 7th month of development, most oogonia have transformed into primary oocytes within follicles.
o Many primary oocytes are lost through a slow continuous degenerative process called atresia which continues
through a woman’s reproductive life.
o At puberty the ovaries contain around 300,000 oocytes.
o During each menstrual cycle, only 1 oocyte resumes meiosis, thus only about 450 oocytes are liberated from
ovaries by ovulation while all others degenerate through atresia.
Ovarian follicles:
o Consists of 1 oocyte surrounded by 1 or more layers of epithelial cells within a basal lamina.
o The follicles formed during fetal life are called primordial follicles and consist of a primary oocyte enveloped by a
single layer of flattened follicular cells.
o
, Follicular growth and development:
o Beginning in puberty with the release of FSH from pituitary, a small group of primordial follicles each month
begins a process of follicular growth.
o Oocyte differentiation includes the following:
Growth of the cell and nuclear enlargement
Mitochondria becoming more numerous and uniformly distributed
RER becoming much more extensive and Golgi complexes enlarging and moving peripherally
Formation of specialized secretory granules called cortical granules containing various proteases.
o Follicular cells undergo mitosis and form a simple cuboidal epithelium around the growing oocyte thus the follicle
will now be called a uni-laminar primary follicle.
, o These follicular cells continue to proliferate, forming a stratified follicular
epithelium called the granulosa (these cells communicate through gap
junctions). Follicular cells are now termed granulosa cells and the follicle
is called a multilaminar primary follicle.
o Zona pellucida: between the oocyte and the first layer of granulosa cells
and has extracellular accumulates and contains 4 glycoproteins secreted
by the oocyte.
Its components ZP3 and ZP4 are important sperm receptors binding specific
proteins on the sperm surface and inducing acrosomal activation.
Stromal cells outside each growing primary follicle differentiate to form
follicular theca:
1. Theca interna:
o Typical steroid-producing cells secreting androstenedione.
This hormone is then converted to estradiol by the enzyme aromatase in
the granulosa cells. It is FSH-dependent.
This estrogen returns to the thecae and stroma around the follicle, then
distributed into the body.
2. Theca externa:
o Is more fibrous
o Has fibroblasts and smooth muscle merging with surrounding stroma.
As primary follicles grow, small spaces appear between the granulosa layers
as the cells secrete follicular fluid (liquor folliculi).
1. When all these spaces merge they form the antrum
2. Such follicles with an antrum are called vesicular or antral follicles.
The granulosa cells that immediately surround the zona pellucida make up the corona radiate and accompany the
oocyte when it leaves the ovary at ovulation.
Mature or graafian follicle (preovulatory follicle) has a big antrum and very thin granulosa layer. It also has thick
thecal layers and normally develops from a primordial follicle over a period of around 90 days.
Follicular atresia:
o Process where follicular cells and oocytes die and are disposed of by phagocytic cells.
o Atresia involves detachment of the granulosa cells, autolysis of oocyte and collapse of the zona pellucida.
o It is most prominent just after birth when levels of maternal hormones decline rapidly, and during pregnancy and
puberty.
o During a menstrual cycle, one follicle becomes dominant and develops more.
The female reproductive system consists of the paired ovaries and oviducts (or uterine tubes), the uterus, the
vagina, and the external genitalia
Beginning at menarche, when the first menses occurs, the reproductive system undergoes monthly changes in
structure and function that are controlled by neurohormonal mechanisms
Ovaries:
o Each ovary is covered with simple cuboidal epithelium
This overlies that tunica albuginea
o Its cortex has many ovarian follicles
o The internal medulla contains loose connective tissue and blood vessels entering the organ through the hilum.
Early development of the ovary:
o Primordial germ cells migrate from the yolk sac to the gonadal primordial where they divide and differentiate as
oogonia.
o Primary oocytes are arrested at prophase of meiosis and are surrounded by follicular cells to form an ovarian
follicle.
o By 7th month of development, most oogonia have transformed into primary oocytes within follicles.
o Many primary oocytes are lost through a slow continuous degenerative process called atresia which continues
through a woman’s reproductive life.
o At puberty the ovaries contain around 300,000 oocytes.
o During each menstrual cycle, only 1 oocyte resumes meiosis, thus only about 450 oocytes are liberated from
ovaries by ovulation while all others degenerate through atresia.
Ovarian follicles:
o Consists of 1 oocyte surrounded by 1 or more layers of epithelial cells within a basal lamina.
o The follicles formed during fetal life are called primordial follicles and consist of a primary oocyte enveloped by a
single layer of flattened follicular cells.
o
, Follicular growth and development:
o Beginning in puberty with the release of FSH from pituitary, a small group of primordial follicles each month
begins a process of follicular growth.
o Oocyte differentiation includes the following:
Growth of the cell and nuclear enlargement
Mitochondria becoming more numerous and uniformly distributed
RER becoming much more extensive and Golgi complexes enlarging and moving peripherally
Formation of specialized secretory granules called cortical granules containing various proteases.
o Follicular cells undergo mitosis and form a simple cuboidal epithelium around the growing oocyte thus the follicle
will now be called a uni-laminar primary follicle.
, o These follicular cells continue to proliferate, forming a stratified follicular
epithelium called the granulosa (these cells communicate through gap
junctions). Follicular cells are now termed granulosa cells and the follicle
is called a multilaminar primary follicle.
o Zona pellucida: between the oocyte and the first layer of granulosa cells
and has extracellular accumulates and contains 4 glycoproteins secreted
by the oocyte.
Its components ZP3 and ZP4 are important sperm receptors binding specific
proteins on the sperm surface and inducing acrosomal activation.
Stromal cells outside each growing primary follicle differentiate to form
follicular theca:
1. Theca interna:
o Typical steroid-producing cells secreting androstenedione.
This hormone is then converted to estradiol by the enzyme aromatase in
the granulosa cells. It is FSH-dependent.
This estrogen returns to the thecae and stroma around the follicle, then
distributed into the body.
2. Theca externa:
o Is more fibrous
o Has fibroblasts and smooth muscle merging with surrounding stroma.
As primary follicles grow, small spaces appear between the granulosa layers
as the cells secrete follicular fluid (liquor folliculi).
1. When all these spaces merge they form the antrum
2. Such follicles with an antrum are called vesicular or antral follicles.
The granulosa cells that immediately surround the zona pellucida make up the corona radiate and accompany the
oocyte when it leaves the ovary at ovulation.
Mature or graafian follicle (preovulatory follicle) has a big antrum and very thin granulosa layer. It also has thick
thecal layers and normally develops from a primordial follicle over a period of around 90 days.
Follicular atresia:
o Process where follicular cells and oocytes die and are disposed of by phagocytic cells.
o Atresia involves detachment of the granulosa cells, autolysis of oocyte and collapse of the zona pellucida.
o It is most prominent just after birth when levels of maternal hormones decline rapidly, and during pregnancy and
puberty.
o During a menstrual cycle, one follicle becomes dominant and develops more.
