Female Reproductive System
Female Reproductive System
The organs of the female reproductive system produce and maintain female sex cells (egg cells or ova), transporting these cells to a place where they can be fertilized by sperm, to a developing embryo. Provide a favorable environment, and transfer the embryo out. At the end of the growth period, and the production of female sex hormones. The female reproductive system includes the ovaries, fallopian tubes, uterus, vagina, accessory glands, and external organs.
- Ovaries
- Gentle track
- External genitalia
- Female sexual response and hormonal control
- Mammary gland
Ovaries
There are the two ovaries that are the primary female reproductive organs, or gonads. Each ovary is a solid, oval structure about the size and shape of an almond, about 3.5 cm long, 2 cm wide, and 1 cm thick. The ovaries are located in shallow depressions, called ovarian fossae, on each side of the uterus, in the lateral walls of the pelvic cavity. These primary female reproductive organs are held loosely in place by peritoneal ligaments.
Structure
The ovary is covered externally by a layer of simple cuboidal epithelium called the germinal (ovarian) epithelium. It is actually the visceral peritoneum that envelops the ovary. Beneath this layer is a dense connective tissue capsule, the tunica albuginea. The ovarian substance is clearly divided into an outer cortex and an inner medulla. The cortex appears more dense and granular due to the presence of multiple ovarian follicles in various stages of development. Each follicle contains an oocyte (a female germ cell). The medulla is a loose connective tissue that contains abundant blood vessels, lymphatic vessels, and nerve fibers.
Oogenesis
Female sex cells, or gametes, develop in the ovary by a form of meiosis called oogenesis. The sequence of events in oogenesis is similar to that of spermatogenesis, but the timing and end result is different. Early in embryonic development, primordial germ cells in the ovary differentiate into oogonia. They divide rapidly to form thousands of cells, still called oogonia, which contain a full complement of 46 (23 pairs) chromosomes. Oogonia then enter the developmental phase, enlarges, and becomes primary oocytes. Diploid (46 chromosomes) primary oocytes replicate their DNA and begin the first meiotic division, but this process stops in prophase and the cells remain in this suspended state until puberty. Many primary oocytes degenerate before birth, but despite this reduction, both ovaries contain approximately 700,000 oocytes at birth. This is a lifetime supply, and will not evolve further. This is quite different from males in which spermatogonia and primary spermatocytes continue to develop throughout reproductive life. By puberty, the number of primary oocytes further decreases to about 400,000.
From the onset of puberty, under the influence of follicle-stimulating hormone, several primary oocytes begin to grow again each month. It appears that one of the primary oocytes outgrows the other and initiates meiosis I again. Other cells degenerate. The giant cell undergoes asymmetric division so that almost all of the cytoplasm, organelles, and half of the chromosomes go into one cell, which becomes a secondary oocyte. The other half of the chromosome goes into a small cell called the first polar body. The secondary oocyte begins at the second meiotic division, but the process stops at metaphase. At this point, ovulation occurs. If fertilization occurs, meiosis II continues. Again this is an unequal division with all the cytoplasm going into the ovum, which contains 23 single-stranded chromosomes. A cell smaller than this division is the second polar body. The first polar body also normally divides in meiosis I to produce two smaller polar bodies. If fertilization does not occur, the second meiotic division is never completed and the secondary oocyte degenerates. Here again, there are clear differences between males and females. In spermatogenesis, four viable sperm are produced from each primary spermatocyte. In oogenesis, only one viable fertilizable cell develops from a primary oocyte. The remaining three cells are polar bodies and they degenerate.
Ovarian Follicle Development
An ovarian follicle consists of a developing oocyte surrounded by one or more layers of cells called follicular cells. At the same time that the oocyte is progressing through meiosis, similar changes are occurring in the follicular cells. The primordial follicle, which consists of a primary oocyte surrounded by a layer of flattened cells, develops in the embryo and is the stage that is present in the ovary at birth and throughout childhood.
Beginning at puberty, the follicle-stimulating hormone stimulates changes in primordial follicles. The follicle cells become cuboidal, and the primary oocyte enlarges and is now a primary follicle. Follicles continue to grow under the influence of follicle-stimulating hormone, and follicular cells proliferate to form several layers of granulosa cells surrounding the primary oocyte. Most of these primordial follicles degenerate along with the primordial oocytes within them, but usually one continues to develop each month. The granulosa cells begin to secrete estrogen and a cavity or antrum forms inside the follicle. When the antrum begins to develop, the follicle becomes a secondary follicle. The granulosa cells also secrete a glycoprotein substance that forms a clear membrane, the zona pellucida, around the oocyte. After about 10 days of development, the follicle is a mature vascular (Graafian) follicle, which forms a "blister" on the surface of the ovary and contains a secondary oocyte ready for ovulation.
Ovulation
Ovulation, signaled by a luteinizing hormone from the anterior pituitary, occurs when a mature follicle on the surface of the ovary ruptures and releases the secondary oocyte into the peritoneal cavity. The ovulated secondary oocyte, which is ready for fertilization, is still surrounded by the zona pellucida and a few layers of cells called the corona radiata. If it is not fertilized, the secondary oocyte degenerates within a few days. If a sperm passes through the corona radiata and zona pellucida and enters the cytoplasm of the secondary oocyte, a second meiotic division again forms a polar body and a mature ovum.
After ovulation and in response to luteinizing hormone, the part of the follicle in the ovary enlarges and transforms into the corpus luteum. The corpus luteum is a glandular structure that secretes hormones like progesterone and some estrogen. Its fate depends on whether fertilization occurs. If fertilization does not occur, the corpus luteum remains active for about 10 days. It then begins to degenerate into the corpus Albicans, which is essentially scar tissue, and its hormone production stops. If fertilization occurs, the corpus luteum remains intact and continues its hormonal functions until the placenta develops enough to secrete the necessary hormones. Again, the corpus luteum eventually degenerates into the corpus Albicans, but it remains active for a long time.
Genital Tract
Fallopian Tubes
There are two uterine tubes, also called fallopian tubes or fallopian tubes. Each ovary has a tube associated with it. The end of the tube near the ovary expands to form a funnel-shaped infundibulum, surrounded by finger-like extensions called fimbriae. Because there is no direct connection between the infundibulum and the ovary, the oocyte enters the peritoneal cavity before entering the fallopian tube. At ovulation, the fimbriae increase their activity and create a current in the peritoneal fluid that helps propel the oocyte into the fallopian tube. After entering the fallopian tube, the oocyte is moved by the rhythmic beating of the cilia on the epithelial lining and the peristaltic action of the smooth muscles in the wall of the tube. The journey through the fallopian tubes takes about 7 days. Since the oocyte is only fertilized for 24 to 48 hours, fertilization usually takes place in the fallopian tube.
Uterus
The uterus is a muscular organ that receives the fertilized oocyte and provides a suitable environment for the developing embryo. Before the first pregnancy, the uterus is about the size and shape of a pear, with the narrow part in the inferior direction. After childbirth, the uterus usually enlarges, then shrinks back after menopause.
The uterus is lined with the endometrium. During menstruation, the stratum function of the endometrium ceases. The deep stratum basale provides the basis for functional remodeling.
Vagina
The vagina is a fibromuscular tube, about 10 cm long, that extends from the cervix to the outside of the uterus. It is located in females between the rectum and the urinary bladder. Because the vagina tilts upward and the cervix tilts upward, the cervix enters the vagina at almost a right angle. The vagina serves as a passageway for menstrual flow, receives an erect penis during intercourse, and is the birth canal during childbirth.
External Genitalia
The external genitalia is accessory structures of the female reproductive system that lie outside the vagina. They are also called vulva or pudendum. The external genitalia includes the labia majora, mons pubis, labia Maura, clitoris, and glands within the vestibule.
The clitoris is an organ, similar to the male penis, that responds to sexual stimulation. Behind the clitoris, the urethra, vagina, paraurethral glands, and more vestibular glands open into the vestibule.
Female Sexual Response & Hormone Control
Female sexual responses include arousal and orgasm, but not ejaculation. A woman can get pregnant without orgasm.
Follicle-stimulating hormone, luteinizing hormone, estrogen, and progesterone play an important role in regulating the functions of the female reproductive system.
At puberty, when the ovaries and uterus mature enough to respond to hormonal stimulation, certain stimuli trigger the hypothalamus to release the gonadotropin-releasing hormone. This hormone enters the bloodstream and travels to the anterior pituitary gland where it stimulates the release of follicle-stimulating hormone and luteinizing hormone. These hormones, in turn, affect the ovaries and uterus and start the monthly cycle. A woman's reproductive cycle lasts from menstruation to menopause.
The monthly ovarian cycle begins with the development of the follicle during the follicular phase, continues with the development of the ovum during the ovulatory phase, and ends with the development and rupturing of the corpus luteum during the luteal phase.
The uterine cycle coincides with the ovulation cycle. The uterine cycle begins with menstruation during the menstrual phase, continues with the repair of the endometrium during the proliferative phase, and ends with the development of glands and blood vessels during the secretory phase.
Menopause is when a woman's reproductive cycle stops. This stage is marked by decreased levels of ovarian hormones, increased levels of pituitary follicle stimulating hormone, and low levels of luteinizing hormone. Changing hormone levels are dangerous and responsible for the symptoms associated with menopause.
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- Reproductive Systems
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- Compatibility model of Female Reproductive System
- Anatomy and physiology of Female Reproductive System
- Comparative Female Reproductive System
- Reproductive Systems of Animals
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- Reproductive System slides
- Female Reproductive System presentations
- Female Reproductive System Notes
- Female Reproductive System lectures