Ovaries (Latin: ovarium) are women's leading hormonal endocrine glands, part of the endocrine system, where ovocytes are maturing, the egg is produced and sex hormones - estrogens and progestogens - are secreted. The ovaries release the ovocyte that travels through the fallopian tube ending up in the uterus. The hormones affect the menstrual cycle and fertility.
Ovaries, female gonads, have almond shapes, and they are pair organs located on both sides of the body. Their length is 3-5 cm, width 1.5-3 cm, thickness 0.7-1.5 cm, and weight 5-8 grams. Ovaries are located in the small pelvis, almost vertically against the pelvis's lateral side across the sacroiliac joint, in the peritoneal cavity.
As for the uterus, the ovaries are located along the lateral wall of the uterus in a region known as the ovarian fossa. The ovaries are connected to the uterus via the fallopian tubes. The ovaries are somewhere white in color. Ovaries have two poles, two surfaces, and two margins.
The ovarian poles:
- Superior pole - also called the tubal pole. It is located by the infundibulum of the fallopian tubes. This pole is covered by the fimbriae of the fallopian tube. It is attached to the suspensory ligament of the ovary.
- Inferior pole - also called the uterine pole. It is located more inferiorly than the other pole and towards the uterus. The inferior pole is attached by the ligament of the ovary.
The ovarian surfaces:
- Medial surface - facing the small pelvis cavity. Fimbriae of the fallopian tubes are lying against this surface.
- Lateral surface - towards the pelvis lateral wall, which is spread out with parietal peritoneum.
The ovarian margins:
- Anterior margin - mesovarium. Meosvarium is a part o the broad ligament of the uterus covering the ovaries to their anterior up till the posterior part of the broad ligament. In the middle of the margin is the hilum of the ovary, through which blood vessels, nerves, and lymphatic vessels go.
- Posterior margin - it is free, without any connections, and is exposed to the peritoneal cavity.
Fixating structures of the ovaries
The ovaries are fixated in the small pelvis with the help of ligaments.
The ligament of the ovary
The ligament of the ovary connects the inferior pole of the ovary to the cornu of the uterus, below the place where the fallopian tube enters the uterus. The ligament lies between layers of the broad ligament of the uterus. The ligament of the ovary has the consistency of a cord.
The ligament has connective tissues, elastic fibers, blood vessels, and smooth muscle cells within it. The elastic fibers and smooth muscle cells allow the ligament to change its length slightly. As the urinary bladder volume increases, the uterus is bent back; the ligament of the ovary stretches so that the ovary can stay in its location.
The suspensory ligament of the ovary
The suspensory ligament of the ovary is a fold of the peritoneum laterally from the broad ligament of the uterus. The ligament stretches from the lateral wall of the pelvis to the superior pole of the ovary. Within the ligament are the ovarian artery, the ovarian vein, the ovary plexus from the celiac plexus.
Mesovarium is a duplication of the posterior fold of the broad ligament of the uterus. From the posterior surface of the broad ligament of the uterus to the mesovarium or anterior margin of the ovary. Between its folds are nerves, blood vessels, lymphatic vessels.
The ovaries are located in the peritoneal cavity, but the peritoneum is not covering them. The peritoneum is attached to the ovaries in the form of a mesovarium. The ovaries have four layers. The outer layer or the surface is formed by cuboidal epithelial cells known as the germinal epithelium. The layer below it is made of collagenous connective tissues, which is known as tunica albuginea.
The parenchyma itself is divided into an ovarian cortex and an ovarian medulla—no distinct border between these. Within the ovarian cortex connective tissues, the follicles of the ovary are located. In the ovarian medulla lies loose connective tissue, blood vessels, lymphatic vessels, and nerve branches. The most middle part is called the stroma. The stroma is made of loose connective tissues supplied with blood vessels. The stroma is also what fills the space between ovarian follicles.
The ovaries have two main functions: the production and maturation of ovocytes and the secretion of hormones. The production of the ovocyte is a process with different types of follicles and ovocytes along the way. The hormones secreted by the ovaries take part in the ovocyte production, endometrial lining.
The follicles of the ovary and oogenesis
In the outer side of the cortex, beneath the tunica albuginea, are immature ovocytes or primary ovarian follicles. Every newborn girl has a significant amount of these follicles, around 50 000 - 80 000, in every ovary. With every year, this number decreases, so each ovary has only about 10 000 follicles at the time of puberty.
When girls reach sexual maturity, ovaries start to work in cycles. The average cycle is 28 days (the period between the two first days of menstrual bleeding). During the reproduction period between age 13 and 50, in every cycle, only one, in rare cases, two, follicles are matured, and ovulation happens. So from puberty till the climax, approximately 400-450 follicles get complete maturation and ovulation. As the climax starts, the growth and development of ovocytes stop.
Oogenesis is the production of female gametes. Similar to spermatogenesis, oogenesis engages meiosis and produces haploid gametes. Unlike spermatogenesis, which is continuing process, oogenesis happens in a specific rhythm called the ovarian cycle. Only one functional gamete is made from the original germ cell. The other daughter cells become small polar bodies and eventually disintegrate.
Like those of the male, the female primordial germ cells arise from the embryo's yolk sac. These cells eventually differentiate into oogonia. Oogonia keep multiplying till the fifth gestation month and reach up to six to seven million, after which they stop developing with starting again shortly before birth.
Before birth, some of the oogonia transforms into primary ovocytes and continues development until meiosis I. Primary ovocytes that will not be stimulated to go through the meiosis I division are kept in small follicles called primordial follicles. The primordial follicle has a single layer of squamous follicular cells surrounding the ovocyte. Approximately three days before the menstrual period starts, the pituitary gland secrets follicle-stimulating hormone. If primary ovocytes respond to that, they will get larger, and the follicular cells will divide to produce the follicular epithelium. These new follicles are called the primary ovarian follicles.
In the primary follicles, the follicular cells differentiate into cuboidal epithelium and become stratified called granulosa cells. The stroma by the follicle turns into a fibrous capsule - theca folliculi - divides in theca interna and theca externa. The theca and granulosa cells together synthesize estrogens. Most primary follicles degenerate without further development, while some primary follicles continue growing in size as the granulosa cells secrete estrogen-rich fluid. The fluid eventually forms one big cavity called the antrum. At this point, follicles are known as the secondary ovarian follicles. This happens when menstruation ends around day 5.
Around day 10, only one follicle survives. It increases in size and bulges from the ovarian surface. This is the follicle that will ovulate. The ovocyte in this secondary follicle is connected to the follicular wall with the help of a mound of granulosa cells called cumulus oophorus. The ovocyte and the corona radiata, the inner part of the cumulus oophorus cells, are separated by a thin gel-like layer of proteins and polysaccharides - zona pellucida.
Under the stimulation of follicle-stimulating hormone from the anterior pituitary, the follicular cells secrete increasing estrogen amounts as the follicles grow. The follicular cells produce estrogen from its precursor testosterone, supplied by a layer of cells immediately outside the follicle called the theca interna.
Now the primary ovocyte can complete its division through meiosis I. This division does not form two complete cells. Only one of the cells gets a significant amount of cytoplasm - the secondary ovocyte. The other smaller cell forms are called the first small polar body, which eventually fragments and disappears. The second ovocyte begins meiosis II, but it is arrested in it and is in this state unless fertilization happens.
If fertilization happens, meiosis II is completed, an ovum is formed, and a second polar body is formed. If fertilization does not occur, the ovocyte dies without finishing meiosis II.
The term ovum can be used only when the secondary ovocyte has undergone meiosis II. Meiosis II occurs when the sperm cell has penetrated the ovocyte. Only within matured ovocyte or ovum, after the second polar body has been released, the fusion of two nuclei can happen to form a zygota.
Ovulation is the release of an ovocyte that usually happens around the tenth to the fourteenth day following the first day of the menstrual cycle. One follicle has matured fully to become a vesicular ovarian follicle which is 1 cm in diameter. Other secondary follicles regress during menstrual cycle and become atretic. The vesicular ovarian follicle is so large that it forms a bulge on the surface of the ovary.
Under the stimulation of luteinizing hormone, this follicle ruptures and extrudes the secondary ovocyte, now can be called the egg, into the peritoneal cavity near the fallopian tube's opening in the process of ovulation. The ovocyte is caught by the fimbriae of the fallopian tube and enters the fallopian tube. After the ovulation, the corpus luteum forms.
After the ovulation happens, usually during the middle of the cycle, the ex-vesicular follicle's wall deflates. Blood from the blood vessels in the ruptured connective tissue enters into the center of the follicle and, together with the follicle's leftovers, forms the corpus hemorrhagicum. A blood clot develops and is absorbed, leaving only connective tissues.
After a while, corpus hemmorrhagicum changes into corpus luteum, which differentiates into an active endocrine gland over a couple of days. Its yellow name is because a yellow lipid accumulates in the theca interna cells. These cells are now called lutein cells. The corpus luteum secretes progesterone that stimulates the uterus to be ready for a possible pregnancy. The corpus luteum has two types:
- If fertilization happens, menstruation or fake corpus luteum develops. It functions till the ovary cycle's second half until the 27th day of the cycle. Afterward, it gets absorbed, and connective tissue appears.
- If fertilization does not happen, corpus luteum graviditatis or real corpus luteum develops. It is secreting very actively during the first four months of the pregnancy. After the pregnancy, it gets absorbed, and a scar appears. In the scar, calcium salt can settle, forming corpus albicans that can stay in the ovary until five years.
In both cases, the absorption leaves small scars. Ovaries work in a cycle with 2 phases. The first phase is during the first half of the cycle and is called the follicular phase, while the second phase starts on the second half or 14th day of the cycle and is called the corpus luteum phase.
The ovaries secrete the steroids - estrogen, progesterone, androgens - and the peptides - inhibin, activin, relaxin. Estrogen and progesterone play an essential part in keeping the uterus endometrial lining and are a part of the negative feedback regulation of pituitary hormone release. The function of peptide hormones is not yet completely understood.
Theca cells secrete androgens due to the luteinizing hormone from the pituitary gland, while granulosa cells convert androgens to estrogens.
Estrogens affect secondary sex characteristics, bone, metabolism, and the brain. The estrogens are needed for the development of the secondary sexual features of women. The growth of the breast ducts and pigmentation of the areoles is stimulated by the estrogens during puberty and pregnancy.
The estrogens keep the structure of the vaginal mucosa and stimulate cervical mucus production. They also take part in the development of the ovarian follicles and stimulation of endometrial cell proliferation. The estrogen's effect on the brain is to increase libido. Also, bone health depends on the estrogens, especially during puberty.
Progesterone is secreted by the corpus luteum, its lutein cells. It is pregnancy's main hormone until week eight, when the placenta takes over. Progesterone is needed for maintaining the pregnancy. Progesterone provides the right structure of the uterus for implantation of the embryo. Progesterone is known to raise body temperature.
Even though androgens are thought to be male sex hormones, they still have functions in women. Androgens have a part in the production of estrogens. Aromatase, an enzyme, converts androgens to estrogens in the ovaries and fat tissue. Androgens help the development of pubic and axillary hair, controlling libido. If a woman has too much androgens, it can cause masculinization and problems with the menstrual cycle.
Ovarian peptide hormones
Inhibin and activin are produced by Sertoli cells in the testis in men, but in women, they are made by the ovaries. The ovaries also secrete relaxin.
Inhibin is a glycoprotein that can inhibit follicle-stimulating hormone. Inhibin is secreted by the granulosa and theca cells. Inhibin could also be involved in the selection of follicles. Increased inhibin levels can be seen in early menopause.
Activin is a growth factor beta-peptide. Endometrium produces great amounts of activin. During the menstrual cycle it allows the development of endometrium.
Relaxin stimulates follicular development and ovocyte maturation, as well as helps the implantation of the embryo.
The menstrual cycle
The menstrual cycle can be described as hormonal and physiological changes that start with the endometrium's shedding, including the release of the matured ovocyte from the follicle. The menstrual cycle is the basic unit of reproductive time. On average, the cycle lasts 28 days. The cycle's length can vary within individuals but is quite regular for an individual. During puberty and the perimenopausal period, the cycle can be longer. The two main phases are the follicular phase and the luteal phase. Two different phases, the menstrual phase, and the ovulation, overlap or are a part of the two main phases.
The menstrual phase
This phase is a part of the follicular phase. The menstrual phase and the follicular phase starts on day one of the menstrual cycle. The endometrium shedding begins on day one. The endometrium lining that was developed during the previous cycle is shedded through the vagina together with small amounts of blood. The bleeding or the menstrual phase lasts four to seven days. This phase usually is painful, which is caused by vasospasms.
The follicular phase
The follicular phase starts on day one of the menstrual cycles and lasts till ovulation. Changes in the uterus and follicle maturing are happening during this phase. Ovarian follicles secrete estrogens that make the endometrium proliferate and gain an extensive blood supply. It is known as the decidualization of the endometrium. Selected follicles are maturing, so during ovulation, the ovocyte can be released. The developing follicle is secreting increased amounts of estrogen.
During ovulation, as mentioned before, the ovocyte is released from the ovary. Luteinizing hormone stimulates the release of prostaglandins and inflammatory cytokines that allows the rupture of the follicle and release of the ovocyte.
The luteal phase
In the luteal phase, the primary hormone is progesterone. This phase follows ovulation, and corpus hemmorrhagicum and corpus lutem are formed. If fertilization happens, the corpus luteum persists and keeps secreting progesterone. If fertilization does not occur, the corpus luteum degenerates, a decrease in progesterone is seen, which causes the shedding of the endometrium and the start of menstrual bleeding.
Vasculature and innervation of the ovaries
The ovaries receive their blood supply through two arteries - the ovarian branch of the uterine artery that goes through the mesovarium and the ovarian artery that goes through the suspensory ligament. The ovarian arteries start by branching off the anterolateral side of the abdominal aorta at the level of L2.
They are bilateral arteries below the renal arteries. They cross the ureters in front of them and reach the ovaries through the suspensory ligament of the ovary, and enters the ovaries through their superior poles. Before reaching the ovary, ovarian arteries branch to the fallopian tube. Afterward, the ovarian artery and its tubal branches form an anastomosis with their corresponding uterine artery branches and give off multiple small arteries that enter the ovaries.
The ovarian veins start as a pampiniform plexus located in the mesovarium. Then they blend to form two left and two right ovarian veins. These veins also go within the suspensory ligament of the ovary. Both veins on each side converge together and form one left and one right ovarian vein during their path. These veins then go superomedially, crossing ureters as arteries do. The left ovary vein ends in the renal vein, while the right ovary vein ends into the inferior vena cava.
The ovarian artery is innervated by the postganglionic nerve fibers of the aortic ganglia located at the beginning of the ovarian arteries. The fibers are responsible for vasoconstriction. The aortic ganglia synapses with preganglionic fibers of the lesser splanchnic nerves.
Pelvic splanchnic nerves send preganglionic fibers to the inferior hypogastric plexus, which postganglionic fibers are responsible for the parasympathetic innervation of the ovaries. Postganglionic fibers move alongside the uterine arteries and are accountable for vasodilatation.
Even if the ovaries were not innervated, they would still perform ovulation as hormones regulate ovulation.
The lymphatic drainage has three ways to leave the ovaries. One way is superiorly alongside the ovarian artery draining the lymph into the para-aortic lymph nodes. Drainage can also happen inferiorly via the inguinal canal to the superficial inguinal node's medial group. The third way is that lymph gets drained horizontally to the other ovary crossing the uterine fundus.
The most common ovary diseases
Ovarian diseases can happen to young and older women, with more cases in young. Ovarian disorders are considered to be endocrine diseases due to the organs' functions. The most common ovarian conditions are endometriosis, ovarian cysts, ovarian epithelial cancer, ovarian germ cell tumors, polycystic ovarian syndrome, and disorders of the menstrual cycle.
Endometriosis can be a painful disorder when tissue typically found in the uterus grows outside the uterus. Most commonly, endometriosis affects ovaries, fallopian tubes, or peritoneal spaces. Despite that the tissue grows outside the uterus, the endometrium still thickens, breaks down, and causes menstrual bleeding; only in these cases, the blood stays inside the body. There is no specific cause for endometriosis, but the possible ones are:
- retrograde menstruation - menstrual blood containing endometrium flow backward to the fallopian tubes or the pelvic cavity
- transformation of peritoneal cells - possible that hormones stimulate the conversion of peritoneal cells into endometrial-like cells
- surgery - after C-section or hysterectomy, endometrial cells can attach to the surgical scar
- endometrial cell transport - endometrial cells travel through the blood vessels or lymphatic vessels
- immune system disorders.
There are also risk factors for the development of endometriosis:
- the period starting at an early age
- later menopause
- short menstrual cycles (<27 days)
- heavy menstrual bleeding (> 7 days)
- low body mass index
- never giving birth
- endometriosis in relatives
- reproductive tract abnormalities
Endometriosis is usually painful, but apart from that, women can also experience dysmenorrhea (painful periods), pain during intercourse, pain while urinating or during bowel movements, excessive menstrual bleeding, infertility, fatigue, diarrhea, constipation, bloating.
Treatment for endometriosis usually is medication and surgery. Pain medication with nonsteroidal anti-inflammatory drugs, hormone therapy using hormonal contraceptives, gonadotropin-releasing hormone agonists and antagonists, progestin therapy, aromatase inhibitors. As for surgery, it can be conservative in removing the endometriosis implants while saving the uterus and ovaries. Sometimes hysterectomy with removal of ovaries is needed.
Ovarian cysts are sacs filled with fluid in the ovary or on its surface. Cysts can be found in many women. Most of the time, they are painless, harmless, and without causing discomfort.
Risk factors for the development of cysts are:
- hormonal problems
- severe pelvic infection
- previous ovarian cyst.
Ovarian cysts usually develop due to the menstrual cycle; they are called functional cysts and are the most common type. Typically, follicles form in the ovaries, but if the normal follicle keeps growing, it turns into a cyst. Functional cysts can be divided into a follicular cyst and a corpus luteum cyst. Other types of cysts are not related to the menstrual cycle, like dermoid cyst (contains different tissue - hair, teeth, skin), cystadenomas (filled with water or mucous), endometriomas (during endometriosis).
Cysts are usually painless and can go away by themselves. If the cyst is larger, women can experience pelvic pain, fullness in the abdomen, bloating, in rare cases, fever and vomiting.
Treatment can be started just with a follow-up once a while. From medication, hormonal contraceptives can be used. Surgery might be done for cysts that are not functional, are large, and cause pain.
Ovarian epithelial cancer
Ovarian epithelial cancer is one of the most common ovarian cancer. It develops outside the ovaries and, overtime spreads and can affect other organs. Risk factors for developing cancer:
- age (>50 years)
- family history of ovarian cancer, breast cancer, colon cancer, rectal cancer, or uterine cancer
- the woman herself has breast cancer
- BRCA1/BRCA2 mutation
- Lynch syndrome
- estrogen hormone replacement therapy
Ovarian cancer does not have any early symptoms. Symptoms appear only in the late stages. Possible symptoms: bloatedness, pain in the abdomen or pelvis, trouble eating, feeling full before eating. Treatment is surgery, chemotherapy.
Ovarian germ cell tumor
Most of these tumors are benign; malignant germ cell tumors are rare. Germ cell tumors usually start in the ovarian cells that produce ovocytes.
No specific cause is known, but some suggest congenital disabilities affecting the nervous system, genitals, and urinary tract. Ovarian germ cell tumors are more found in teens or young girls. It has unspecific symptoms:
- swelling in the abdomen
- pain, pressure, fullness in the abdomen
- bleeding from the vagina.
Treatment is with surgery and chemotherapy.
Polycystic ovarian syndrome
Polycystic ovarian syndrome is a hormonal disorder affecting women of reproductive age. In this syndrome, ovaries have many follicles filled with fluid causing failure in ovocyte release. The cause is unknown, but risk factors are excess insulin, low-grade inflammation, hereditary, excess androgens. If a woman has the polycystic ovarian syndrome, the first symptoms will often appear around the first menstrual period. Symptoms can also develop later.
To diagnose the polycystic ovarian syndrome, two of the following signs need to be present:
- irregular periods - infrequent, irregular, prolonged
- excess androgen - increased levels of male hormones
- polycystic ovaries
The polycystic ovarian syndrome can result in:
- sleep apnea
- gestational diabetes
- type 2 diabetes
- depression, anxiety
- abnormal uterine bleeding
- endometrial cancer
Treatment can start with lifestyle changes, like losing weight, more physical activities. For regulation of the menstrual cycle, doctors may prescribe combined contraceptive hormonal pills, progestin therapy. To help women ovulate - metformin, gonadotropins, clomiphene. For excessive hair growth - birth control pills, spironolactone, electrolysis.
Disorders of the menstrual cycle
The most common menstrual cycle disorder is premenstrual syndrome. This syndrome can be painful and unpleasant. Women may experience:
- depression, anxiety, irritability
- vertigo, fainting
- hot flashes
- low libido.
Amenorrhea is the absence of menstrual bleeding for more than three monthly cycles. Primary amenorrhea is when menstruation does not start during puberty. Secondary amenorrhea is when at the beginning woman has had regular periods, but eventually, periods become irregular or absent.
Dysmenorrhea is when severe and frequent cramps and pain accompany period,
Menorrhagia has heavy and prolonged menstrual periods.
Summary on the ovaries
What are the ovaries and their function?
Ovaries are small, almond-shaped pair organs, a part of the female reproductive system. The ovaries are secreting hormones, estrogens, and progesterone, and producing ovocyte that, after fertilization, become an ovum.
Are ovaries important?
The ovaries are an essential part of the female reproductive system and the endocrine system. The ovaries are the place where ovocytes mature that allow further pregnancy. Hormones secreted by the ovaries are responsible for secondary sex characteristics in women, development of ovocyte, ovum and maintaining pregnancy, and preparing the uterine wall for implantation.
Where would you feel pain from your ovaries?
Because the ovaries are located in the lower abdomen, it is most likely that the pain could be felt in the lower abdomen and the pelvis.
Where is ovarian cyst pain felt?
Most ovarian cysts are small and do not cause any pain. If the cyst is bigger and causes pain, it can be felt in the lower right of the pelvis's left side.
What are the symptoms of ovary problems?
The most common symptoms are pelvic pain, pressure or swelling in the abdomen, nausea, vomiting, abnormal bleeding, bloatedness.
How do I know if my ovaries are functioning?
Blood tests like a follicle-stimulating hormone, estradiol can show if there are any problems. Also, a regular menstrual cycle and period are signs that everything is functioning fine, as well as a woman does not have issues with getting pregnant.
What are the four stages of the menstrual cycle?
The first stage is the follicular phase that starts on day one of the menstrual cycle and lasts till day fourteen when ovulation occurs together with the menstrual phase that also begins on day one and lasts for four till seven days. The third phase is ovulation that happens in the middle of the cycle. The last phase is the luteal phase lasting between ovulation until the first day of the next menstrual cycle.
How do you count your menstrual cycle?
The first day of the menstrual cycle is the first day of menstrual bleeding, so this is the best way to start counting. The day before the next menstrual bleeding is the last day of your menstrual cycle.
What is a normal menstrual cycle?
The length of the menstrual cycle differs between each woman, but the average length is 28 days. 21-40 days are also considered a regular cycle.
How many days after your period do you ovulate?
Ovulation usually happens in the middle of the cycle, so if the menstrual cycle is 28 days, then ovulation occurs around day 14.
What happens when you have polycystic ovaries?
If a woman has polycystic ovaries, she will have irregular menstrual periods or no periods at all, excessive hair growth on the face. Weight gain, infertility can also be seen.
How common is epithelial ovarian cancer?
Epithelial ovarian cancer is the most common ovarian cancer. Epithelial ovarian cancer is one of the most common gynecological malignancies, with almost half of the cases occurring in women older than 65. All in all, ovarian cancer itself is not the most common cancer in women.
Why is ovarian cancer aggressive?
Ovarian cancer is aggressive because most of the time, it is diagnosed in the late stage when it has already spread in surrounding tissue and organs. This cancer is quiet and does not show any early signs. Exactly being silent is what makes it aggressive.
How long do you live after being diagnosed with ovarian cancer?
75% of women usually live for at least one year after the diagnosis, but 50% can live up to 5 years. All of this depends on the type and stage of cancer.
Does ovarian cancer spread quickly?
Yes, ovarian cancer spreads very quickly. Even within one-year, cancer can progress from early stage to late stage. Malignant epithelial carcinoma can even spread and grow out of control within weeks or months.