22.2: Female Reproductive System (Internal)

Female Reproductive System (Internal)

Internal Female Genitalia

The female reproductive system includes both internal and external organs. Collectively these organs function to produce female gametes (ova), receive male gametes (spermatozoa), transport the female gametes, provide a location for fertilization to occur, protect and nourish a developing embryo, and deliver a child.

Above: Lateral view of the left side of a female pelvic cavity with the body wall open and organs shown with sagittal sections.

Above: Cadaver image of internal female genitalia, lateral view of the right side with body wall open and pelvic organs with sagittal sections.

Above: Anterior view of internal female reproductive anatomy.

Each ovary is both an exocrine (production of oocytes, immature ova) and an endocrine (production of estrogen and progesterone) organ. The gland can be divided into an outer cortex and inner medulla.

The cortex forms the outer zone of the ovary. The cortex contains follicles, the corpus luteum, and the degenerating elements of these two structures, atretic follicles and corpora albicantia (sing. corpus albicans), respectively. Follicles are epithelial structures that house developing oocytes, the germ cells. Primordial follicles are the smallest follicles, with their follicular cells forming a simple squamous layer surrounding the oocyte. A primary oocyte is housed within each follicle. Primary oocytes can undergo the process of oogenesis (meiotic division process) to become ova.

Above: Thin section of an ovary, magnified by 10x.

Above: (Left) Thin section of an ovary, magnified by 40x. Small follicles are clustered beneath the tunica albuginea, while larger follicles are located deeper in the cortex. (Right) The ovary is covered by a serosa of epithelium overlying a thin connective tissue layer. However, rather than the expected simple squamous epithelium, the epithelium of this serosa is simple cuboidal and is called by the misnomer germinal epithelium. A dense connective tissue layer, tunica albuginea, lies beneath the serosa. Small follicles are located in the cortex beneath the tunica albuginea. Tissue is magnified by 400x.

Above: (Left) Primordial follicles are the smallest follicles, with their follicular cells forming a simple squamous layer. A primary oocyte is housed within each follicle. Primary unilaminar follicles are larger than primordial follicles; their follicular cells have increased in height to form a simple cuboidal or columnar epithelium. The primary oocyte has also increased in size from that present in the primordial follicle. Follicular cells continue to increase in volume and number, becoming a stratified epithelial layer and forming a primary multilaminar follicle. Each primordial and primary follicle contains a primary oocyte. Each oocyte increases in diameter as the follicular cells increase in size and number. Tissue is magnified by 400x. (Right) Secondary follicles form as antral fluid accumulates in spaces among the proliferating follicle (granulosal) cells. (Right bottom) Tissue is magnified by 200x. (Right top) The primary oocyte remains arrested in prophase of the first meiotic division. It is surrounded by a ring of granulosal cells (the cumulus oophorus) and protrudes into the antral space. Tissue is magnified by 400x.

Atretic follicles are the degenerating remains of follicles. Approximately two million primordial follicles, containing primary oocytes, are present at birth, but only 400-450 secondary oocytes are ovulated from Graafian follicles during the reproductive life of a woman; the remaining follicles undergo atresia. The process of atresia can occur at all stages of follicular development.

An ovum is released from a follicle during the process of ovulation (usually one ovum is released every approximately 28 days during reproductive years). The now empty follicle becomes a corpus luteum. The corpus luteum actively secretes progesterone and estrogen from day 15 to day 26 of the menstrual cycle.

The medulla occupies the center of the ovary and is composed of connective tissue containing blood vessels, lymphatic vessels, and nerves that supply the ovary. The exterior of the ovary is covered by a serosa with a simple cuboidal epithelium (mesothelium) overlying a band of dense connective tissue, the tunica albuginea. The ovary is suspended from the broad ligament of the uterus by the mesovarium, through which blood vessels enter and leave the ovary.

Above: (Left) The corpus luteum is present and actively secreting progesterone and estrogen from days 15-26 of the menstrual cycle. A portion of a corpus luteum extends across the bottom of this image of the ovary. This portion of the corpus luteum represents approximately 25-30% of its total volume. Tissue is magnified by 10x. (Right) A corpus albicans is the scar tissue remains of the corpus luteum; its size decreases with age. The corpus albicans is composed of inactive fibroblasts and scar tissue, which gives the corpus alibcans its distinctive white appearance in fresh tissue and eosinophilic staining in typical slide preparations. Tissue is magnified by 100x.

Structure	Location	Function
broad ligament	flat sheet of peritoneum covering internal genitalia anteriorly and posteriorly	provides support for internal genitalia, holding the organs in place
cervix	"neck" between the vagina and the uterus; cervical canal provides passage into the uterus	passage for menstrual fluid to exit the uterus; passage of spermatozoa into the uterus; expands for childbirth
endometrium	inner lining of the uterus; two layers	tissue builds up to prepare for embryo implantation; supports development of an embryo/fetus; built up tissue sheds during menstruation
fimbriae	finger-like projections of the uterine tube extending toward the ovaries	"wave" the egg down the uterine tubes toward the uterus
myometrium	Middle tissue layer of the uterus	three layers of smooth muscle; responsible for labor contractions during childbirth
ovarian ligament	pair of ligaments (right and left) between the ovaries and the uterus	attaches the ovaries to the uterus
ovaries	paired organs with passageways to the uterus by way of uterine tubes; suspended by suspensory ligament and attached to the uterus by ovarian ligament	primary reproductive organ; produces hormones (estrogen and progesterone), storage and development of ova
perimetrium	outer tissue layer of the uterus	continuous with the visceral peritoneum (serosa)
suspensory ligament	pair of ligaments (right and left) between the ovaries and the pelvic wall	supports and holds ovaries in place
urethra	tube between the urinary bladder and the external urethral orifice	removal of urine
uterine tube (fallopian tube)	pair (right and left) of tubes between the uterus and the ovaries; three parts: infundibulum (expansion near ovary, ciliated epithelium moves ova down the tube), ampulla (widened area of tube; where fertilization usually occurs), isthmus (last point of tube; narrow; connects to uterus)	transport of ova and developing embryo to the uterus; site of fertilization; passage for spermatozoa to ova; embryo can implant in uterine tube - called ectopic pregnancy (dangerous condition; endangers mother's life)
uterus	organ located between the bladder and the rectum; dome-shaped fundus; main region called the body	implantation of embryo; development of placenta; fetal development; muscular contractions result in childbirth; buildup and shedding of endometrial lining results in menstruation
vagina	passage from external genitalia to the cervix; lined with stratified squamous epithelium; walls have rugae for stretch/expansion	copulation, childbirth, passageway for menstruation

Above: (Top left) Path of sperm and location of fertilization are shown. (Bottom left) Diagram show the events occurring following fertilization to implantation of the embryo in the uterus. (Right) Internal female genitalia during pregnancy. A specialized organ, the placenta, forms during pregnancy to facilitate transfer of nutrients and waste to and from, respectively, the fetus. The expansion of the uterus during pregnancy causes the other abdominal organs to shift. Vaginal childbirth necessitates passage of the of the fetus through the cervix and vagina.

Fertilization requires spermatozoa to travel through the uterus and to the uterine tube (aka fallopian tube) to reach an ovum (if present). If an ovum is present and spermatozoa are present, a single sperm cell can break through outer layers of the ovum to fertilize it producing a zygote (fertilized ovum). Fertilization occurs in the uterine tube. A zygote begins dividing as it travels through the uterine tube to the uterus. By the time it reaches the uterus, it is a ball of cells called a blastocyst. Implantation of the embryo in the endometrium of the uterus typically occurs 7 to 9 days after fertilization.

Clinical Application: Menstruation

Ova are released from ovaries with the intent for possible fertilization. If a released ovum is not fertilized, the ovum will exit through the vagina and the inner lining of the uterus will be flushed out. This process is called menstruation and occurs about every 28 days. At the beginning of the menstrual cycle, the inner lining of the uterus sheds if the previously released ovum was not fertilized by spermatozoa and implanted to the endometrium. The shedding of endometrium causes vaginal bleeding and is commonly referred to as the “period.” After shedding, the endometrium regrows and thickens in preparation for the next ovum that might be fertilized and implanted in the uterus. This cycle of menstruation is controlled by luteinizing hormone (LH) and follicle- stimulating hormone (FSH) which are produced by the pituitary gland.

Attributions (All Female Reproductive Sections)

• "Anatomy 204L: Laboratory Manual (Second Edition)" by Ethan Snow, University of North Dakota is licensed under CC BY-NC 4.0
• "Digital Histology" by Department of Anatomy and Neurobiology and the Office of Faculty Affairs, Virginia Commonwealth University School of Medicine and the ALT Lab at Virginia Commonwealth University is licensed under CC BY 4.0
• "Female Areola.jpg" by Electric one is licensed under CC BY-SA 3.0
• "Female Reproductive System" by Dongho Kim is licensed under CC BY-NC-SA 4.0
• "Medical gallery of Blausen Medical 2014" by Blausen.com staff is licensed under CC BY 3.0
• "Wiki Images" by https://www.scientificanimations.com/wiki-images/ is licensed under CC BY-SA 4.0