Ovaries

What happens as a result of an LH surge?

A surge of LH from the anterior pituitary triggers the PRIMARY OOCYTE TO RESUME THE FIRST MEITOIC DIVISION. With the completion of this division and extrusion of the first polar body, the oocyte is now a SECONDARY OOCYTE. The secondary oocyte enters meiosis II, but then pauses in metaphase, until fertilization triggers completion of meiosis II. The LH surge also launches the release of the secondary oocyte from the mature follicle (OVULATION), about 24 hrs following the surge. The secondary oocyte (and its corona radiata cells) leave the ruptured follicle at the ovarian surface. They enter the fimbriated end of the oviduct.

What is ovulation?

OVULATION is the process by which the oocyte is released from the mature follicle.

What is the four layers of the ovary is the prominent source of ovarian carcinoma?

The germinal epithelium.

Describe primary unilaminar follicles.

UNILAMINAR PRIMARY FOLLICLES are not dependent on FSH. Local factors stimulate the development of 20-30 primordial follicles into PRIMARY FOLLICLES every month. UNILAMINAR PRIMARY FOLLICLES are composed of a SINGLE LAYER OF CUBOIDAL FOLLICULAR CELLS surrounding a PRIMARY OOCYTE. An amorphous ZONA PELLUCIDA is sometimes visible. Basal lamina is present at interface of follicular cells with STROMA OOCYTE ENLARGES from 30um to ~ 50-80um.

What physiological activity occurs when the follicle is fully mature?

When the follicle is fully mature, a surge of LH causes the PRIMARY OOCYTE to complete the first meiotic division just prior to ovulation. It extrudes the FIRST POLAR BODY and becomes a SECONDARY OOCYTE. THEREFORE ONLY GRAAFIAN FOLLICLES (mature follicles) CONTAIN SECONDARY OOCYTES. = TQ.

What happens to the theca folliculi in the secondary follicles?

THECA FOLLICULI further differentiate into 2 layers: 1. THECA INTERNA: cells are highly-vascularized, steroid-secreting cells. 2. THECA EXTERNA: composed of fibrous connective tissue and smooth muscle; cells are non-secretory. THECA INTERNA cells are, like granulosa cells, responsive to LH. In response to LH stimulation, theca interna cells secrete androgen precursors to estrogens. These precursors enter the GRANULOSA CELLS, where they are converted to estradiol.

What is the definition of menopause?

The absence of menses for 1 year.

Describe the medulla of the ovary.

The central portion of the ovary. Consists mainly of loose connective tissue and blood vessels.

Describe the secondary follicles.

The characteristic feature of the SECONDARY or ANTRAL FOLLICLE is the presence of a fluid-filled cavity called the ANTRUM or FOLLICULAR CAVITY. In the early secondary follicle, the ANTRUM begins forming as fluid-filled spaces among the granulosa cells. The fluid in the antrum is called LIQUOR FOLLICULI. Liquor folliculi contains steroid-binding proteins and numerous hormones, including progesterone, estradiol, inhibin, follistatin and activin.

What is the CORONA RADIATA?

Cumulus oophorus cells that immediately surround the oocyte and contact the ZONA PELLUCIDA are referred to as the CORONA RADIATA.

What is the function of progesterone?

1. Prepares internal sex organs, primarily the uterus, for pregnancy by promoting secretory changes in the endometrium. 2. Progesterone also prepares the mammary gland for lactation by promoting lobular proliferation.

What are the functions of estrogens?

1. Promote growth and maturation of internal and external sex organs and development of typical female secondary sexual characteristics at puberty. 2. Promote mammary gland development and function by stimulating ductal and stromal growth and accumulation of adipose tissue.

What are the two functions of the ovaries?

1. Gametogenesis, the production of female gametes. 2. The production of steroid hormones, principally estrogen and progesterone. This is the endocrine function of the ovaries.

What are the four layers of the ovary going from the outside in?

1. Germinal epithelium. 2. Tunica albuginea. 3. Cortex. 4. Medulla.

What are the 5 types of ovarian follicles?

1. PRIMORDIAL FOLLICLES: Earliest stage of follicle developmentally. 2. PRIMARY FOLLICLES: (2 types) -Unilaminar (single layer of follicular cells) -Multilaminar 3. SECONDARY (ANTRAL) FOLLICLES. 4. MATURE (GRAAFIAN) FOLLICLES.

Note. Make sure you know all of the learning objectives.

Basic structure and subdivisions of the female reproductive system, with emphasis on the ovary. Structure and function of different subdivisions of the ovary. Structure and function of different types of ovarian follicles and their associated cell types. Fundamentals of different stages of oocyte division/ differentiation, and which types of oocytes are found in which types of ovarian follicles. Fundamentals of hormonal control of follicle development and ovulation. Structure and function of corpora lutea and corpora albicans.

What characterizes the primordial follicles?

Characterized by a single layer of squamous FOLLICULAR EPITHELIAL CELLS in close apposition to the OOCYTE (which does not yet have a distinct zona pellucida). Oocytes display a prominent, acentric, vesicular-appearing nucleus (aka germinal vesicle).

Describe ovarian follicles.

Consist of FOLLICULAR CELLS surrounding a single OOCYTE. Follicles provide the microenvironment for the developing oocyte. In a mature, cycling ovary, follicles at all stages of development can be found. There are 5 distinguishable types of ovarian follicles in the ovarian cortex.

Describe the tunica albuginea of the ovary.

Dense layer of CONNECTIVE TISSUE that lies between the germinal epithelium and the cortex.

Describe the germinal epithelium of the ovary.

Erroneous name (no germ cells) given to the single layer of CUBOIDAL epithelium that covers the cortex. The germinal epithelium is separated from the underlying tunica albuginea by a basement membrane. Actually mesothelium (continuation of visceral peritoneum). Also known as OVARIAN SURFACE EPITHELIUM.

What do FSH and Estrogen do to the granulosa cells?

FSH and estrogen stimulate GRANULOSA CELLS to express receptors for LH and to convert androgens (produced by theca interna cells) into estrogens. GRANULOSA CELL LAYERS increase in thickness. Their MICROVILLI penetrate the ZONA PELLUCIDA of the oocyte.

How are secondary follicles formed?

FSH binds to receptors on the granulosa cells of multilaminar primary follicles. Stimulates development of PRIMARY FOLLICLES into SECONDARY FOLLICLES. Thus secondary follicles ARE DEPENDENT ON FSH.

What happens to granulosa and theca interna cells after ovulation?

GRANULOSA CELLS enlarge to become GRANULOSA LUTEIN CELLS, which secrete progesterone and some estrogens. THECA INTERNA CELLS also enlarge under the influence of LH and are now known as THECA LUTEIN CELLS, and also secrete progesterone and some estrogens. THECA LUTEIN CELLS form an interdigitating layer surrounding the GRANULOSA LUTEIN CELLS. Note: The granulosa lutein cells are larger and more numerous than theca lutein cells.

How is the corpus luteum formed?

Following ovulation, the CORPUS LUTEUM forms from the remnants of the Graafian follicle. First the CORPUS HEMORRHAGICUS forms as ruptured blood vessels leak into the remnant of the follicular cavity. Continued high levels of LH (luteinization) cause the corpus hemorrhagicus to convert into the corpus luteum. The CORPUS LUTEUM functions as a temporary endocrine gland. The corpus luteum becomes highly vascularized to subserve its ENDOCRINE FUNCTION. It secretes primarily PROGESTERONE to control the luteal phase of the menstrual cycle. It stimulates the growth and secretory activity of the endometrium.

What is the STRATUM GRANULOSUM?

Granulosa cells form a relatively uniform layer, called the STRATUM GRANULOSUM (MEMBRANA GRANULOSA).

What happens if fertilization and implantation does not occur following ovulation?

If fertilization and implantation do not occur, the corpus luteum remains active for only about 14 days. It then degenerates (undergoes involution), leaving a white scar of connective tissue, called the CORPUS ALBICANS.

Note.

Most types of follicles can be seen in a normal cycling ovary.

Describe primary multilaminar follicles.

Primary multilaminar follicles also not dependent on FSH. Develop from unilaminar primary follicles by PROLIFERATION OF FOLLICULAR CELLS (dependent on ACTIVIN produced by primary oocyte). The follicle is now called a MULTILAMINAR PRIMARY FOLLICLE, and the FOLLICULAR CELLS are also called GRANULOSA CELLS from this stage onward. GRANULOSA CELLS are separated from stromal cells by a BASEMENT MEMBRANE. This basement membrane is around the granulosa cells. A distinctive ZONA PELLUCIDA is now visible around the oocyte and thus below the granulosa cells.

What is the CUMULUS OOPHORUS?

Region of granulosa cells associated with the oocyte is called the CUMULUS OOPHORUS -- projects into the antrum. So it is a subregion of the stratum granulosum.

Describe the stroma cells in the primary multilaminar follicles.

STROMAL CELLS begin to organize in concentric layers around the enlarging follicle at this stage to form the THECA FOLLICULI, which in later stage follicles can be distinguished as 2 layers: THECA INTERNA: Highly vascularized cellular layer. Cells have LH receptors and ultrastructural features of steroid-secreting cells (produce androstenedione, which enters the granulosa cells, where it is converted to estradiol). THECA EXTERNA: mostly fibrous connective tissue. These stroma are outside of the follicle and just surround it like interstitium.

What is another name for the antral follicles?

Secondary follicles.

Describe the changes that have resulted in the formation of the mature follicle.

The mature follicle is very large, extending through the thickness of the ovarian cortex and causing a surface bulge. FOLLICLE GROWS TO 2-2.5 CM IN DIAMETER by the time of ovulation. Granulosa cells continue to develop and produce LIQUOR FOLLICULI. ANTRUM has coalesced into a single cavity

What type of oocytes are in the primordial follicles? Describe these oocytes.

The oocytes in primordial follicles are PRIMARY OOCYTES. During embryonic development, OOGONIA, (progenitors of primary oocytes) migrate into the ovary and undergo mitotic divisions. When they have undergone their final mitotic division they become PRIMARY OOCYTES. Primary oocytes enter prophase of the first meiotic division, and then meiosis is arrested. Since completion of the first meiotic division will not occur until just before ovulation, PRIMARY OOCYTES REMAIN ARRESTED IN PROPHASE OF MEIOSIS I FOR 12-50 YEARS.

What suspends the ovaries?

The ovaries are suspended in the broad ligament of the uterus and by a fold of peritoneum called the mesovarium, which also conveys blood vessels to the ovary.

Describe the cortex of the ovary.

The peripheral portion of the ovary; boundary not well-defined. Contains OVARIAN FOLLICLES in a connective tissue STROMA. = TQ. On a slide with see ovarian follicles in different stages of development. Stroma also contains smooth muscle cells and multipotential cells (will form thecal layers around follicles).

What is the most abundant type of follicle and where is it located in the ovary?

The primordial follicles. Located just beneath the tunica albuginea.

What is the zona pellucida?

The zona pellucida is an acellular layer formed from 3 glycoproteins secreted by the oocyte.