BIOL 302 – Female Reproductive System
Function: production and ovulation of oocytes and secretion of hormones
The surface of the ovary is covered by a single layer of cuboidal epithelium,
called the germinal epithelium. It is continuous with the peritoneal mesothelium.
Fibrous connective tissue forms a thin capsule, the tunica albuginea, immediately
beneath the epithelium.
The ovary is divided into an outer cortex and an inner medulla. The cortex
consists of a very cellular connective tissue stroma in which the ovarian follicles
are embedded. The medulla is composed of loose connective tissue, which
contains blood vessels and nerves.
Ovarian Follicles: consist of one oocyte and surrounding follicular cells. Follicular
development can be divided into a number of stages.
o In meiotic arrest (in prophase); can be arrested up to 50 years
o Round structure, simple squamous layer surrounding oocyte
o The nucleus of the oocyte is positioned eccentric in the cell. It appears
very light and contains a prominent nucleolus.
o First morphological stage that marks the maturation of the oocyte
o Cuboidal or columnar epithelium surrounding the oocyte
o Unilaminar: single layer of cuboidal/low columnar cells; cytoplasm has a
granular appearance, called granulosa cells
o Multilaminar: stratified layer of cuboidal cells
o Zona pellucida around oocyte becomes visible (clear line). Separates the
oocyte from granulosa cells. o Parenchymal cells of the ovary surrounding the growing follicle become
organised in concentric sheaths, the theca folliculi.
o Has completed the first round of meiotic division
o Small fluid-filled spaces become visible between the granulosa cells as the
follicle grows. These spaces enlarge and fuse to form the follicular
antrum, which is the defining feature of the secondary follicle. The oocyte
is now located eccentric in the follicle in the cumulus oophorus, where it is
surrounded by granulosa cells.
o Due to stimulus from pituitary, granulosa cells proliferate into the cumulus
oophorus (pile) and corona radiata (crown)
o The theca folliculi differentiates with the continued growth of the follicle
into a theca interna and a theca externa. Vascularization of the theca
interna improves, and the spindle-shaped cells in this layer start to produce
oestrogens. The theca externa retains the characteristics of a highly
cellular connective tissue with smooth muscle cells.
o During cyclical stages of recruitment, only about 5 from 20 primary
follicles become secondary follicles.
o Follicles that have died.
o Only one will mature to be an oocyte (Graffian) and the rest die off.
o Granulosa cells degenerate from apoptosis and no long support oocyte and
empty space will collapse and scar tissue will develop. o Basement membrane thickens, oocyte degenerates, and granulosa cells die
o Dominant follicle
o Big in size; so big it bulges to surface (called stigma).
o The stigma is characterised by a thinning of the capsule and a progressive
restriction of the blood flow to it. Prior to ovulation the cumulus oophorus
separates from the follicular wall. The oocyte is now floating freely in the
follicular antrum. It is still surrounded by granulosa cells, which form the
corona radiata. The follicle finally ruptures at the stigma and the oocyte is
released from the ovary.
o The ruptured follicle becomes the corpus luteum
o Oocyte undergoes second mitotic division and is stuck in metaphase II
until fertilization. Fertilization triggers completion of meiosis.
o This all happens in response to changes in lutenizing hormone (LH) levels. Corpus Luteum
o The corpus luteum is formed by both granulosa cells and thecal cells after
ovulation has occurred.
o The wall of the follicle collapses into a folded structure, which is
characteristic for the corpus luteum. Vascularization increases and a
connective tissue network is formed. The