Female Reproductive System - Ovary: Structure, Function

The ovaries are small, paired, oval-shaped glands located on either side of the uterus. They produce and store the eggs and also secrete hormones which influence the menstrual cycle and pregnancy. Every month or so, one of the ovaries releases an egg during ovulation. The ovaries release an egg each menstrual cycle until one reaches menopause.

This Story also Contains

1. What is an Ovary?
2. Anatomy of the Ovary
3. Function of the Ovary
4. Ovarian Cycle
5. Common Ovarian Disorders
6. MCQs on Female Reproductive System - Ovary
7. Recommended Video On 'Female Reproductive System - Ovary'

During menopause, the ovaries stop releasing eggs. One is born with all the eggs one will ever have in your lifetime. The ovaries have thousands of ovarian follicles. The follicles are small sacs in the ovary and carry the immature eggs. The process of formation of the ovum and ovulation is under the influence of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), respectively. The ovary is an important topic in the biology subject.

What is an Ovary?

The ovary is a necessary reproductive organ responsible for the production of eggs and the secretion of hormones. Knowing its structure and function is necessary to understand its role within the female reproductive system.

In this system, the ovaries are important in the production of eggs and hormones, which contribute to the development process involved in reproduction and regulating menstrual cycles. Their function is critical for fertility and general reproductive health.

Anatomy of the Ovary

They lie on either side of the uterus and hang off the lateral wall of the pelvis. They are connected to the uterus by the ovarian ligament. The ovary is closer to the fallopian tubes, which receive the eggs when they are released. They lie within the ovarian fossa, a shallow depression on the wall of the pelvis.

Structure of the Ovary

The structure of the ovary is described below:

Cortex

• It constitutes the outermost layer of the ovary

• Contains ovarian follicles at various stages of development

• Extensive connective tissue and vessels

Medulla

• It is the central part of the ovary

• It is made of loose connective tissue

• Has blood vessels, lymphatic vessels, and nerves

Primordial Follicles

• They are the smallest and most numerous

• Completely immature, primary oocytes

• Contains a single layer of cells known as granulosa cells

Secondary Follicles

• Extensive, with multiple layers of granulosa cells

• The first appearance of a fluid-filled cavity is known as an antrum.

Graafian (Mature) Follicles

• Fully developed and ready for ovulation

• Large antrum surrounded by cumulus oophorus cells.

Function of the Ovary

The ovary performs two main functions: of development of the egg and hormonal functions to facilitate reproduction. They also function to regulate the menstrual cycle.

Oogenesis

• Oogenesis begins in fetal development and ends at menopause

• Growth and maturation of the oocyte take place within the ovarian follicles

Stages of Oogenesis

The stages of oogenesis are given below:

Primordial Germ Cells

• Predecessor of the oocyte, produced in early fetal development

Primary Oocytes

• At birth, the result of mitosis and arrest in prophase I

• They are contained within primordial follicles

Secondary Oocytes

• Secondary oocytes are formed after a stage of meiosis and are arrested at the Metaphase II stage

• They are suspended in metaphase II until the time of fertilisation.

Mature ovum

• If fertilisation occurs, the ovum finishes the second meiotic division and an ovum forms.

• The mature ovum fuses with sperm and results in a zygote, to form an embryo.

Hormone Secretion

The hormonal control is explained below-

Estrogen and Production of Progesterone

• The hormones are secreted by the ovarian follicles and the corpus luteum

• Both are secreted by the anterior pituitary under the influence of GnRH secreted by the hypothalamus.

• Causes the development of the endometrial lining during the follicular phase.

• Maintenance of secondary sex characteristics.

Progesterone

• Preparation of the endometrium for implantation during the luteal phase.

• Maintenance of pregnancy via supporting the uterine lining.

Ovarian Cycle

The ovarian cycle is comprised of phases that prepare the body for a potential pregnancy. It is regulated by the hormones. It is important to understand these phases and their regulation to understand the female reproductive system.

Phases of the Ovarian Cycle

The phases of the ovarian cycle are:

Menstrual Phase

• This phase is characterised by the shedding of the endometrial layer.
• The endometrium layer, along with the unfertilised egg, is discarded by the uterus.

Follicular Phase

• Starting from day one of menstrual bleeding, it continues until ovulation, so it roughly extends to 14 days.

• Many follicles within the ovaries begin to grow due to follicle-stimulating hormone.

• One follicle starts and continues to mature while the rest start degenerating.

• The maturing follicle results in the formation of increased production and release of estrogen.

• Mounting estrogen levels stimulate an increase in the thickness of the lining of the uterus, endometrium, in anticipation of the implantation of a fertilised egg.

Ovulation

• Usually, one day, approximately day 14 of the menstrual cycle

• A marked rise in the concentration of Luteinizing Hormone

• The ovum is released, and if fertilised, travels into the uterus

• LH surge is the reliable index for ovulation.

Luteal Phase

• From ovulation to before menstruation starts (for about 14 days)

• The ruptured follicle develops as the corpus luteum. Corpus luteum secretes progesterone, and to some level, estrogen too.

• Progesterone sustains the developed, thickened endometrium, in readiness for implantation.

• If fertilisation doesn't occur, the corpus luteum degenerates and progesterone levels drop.

• This decline in hormone levels triggers the menstruation of the uterine lining.

Regulation of the Ovarian Cycle

The ovarian cycle is under the control of hormonal signals from the hypothalamus and pituitary gland.

Hypothalamus

• It releases Gonadotropin-Releasing Hormone GnRH).

• GnRH acts on the anterior pituitary gland, causing the release of FSH and LH.

Pituitary Gland

• FSH stimulates the growth of follicles in the ovary.

• LH surge causes ovulation and the development of the corpus luteum.

Feedback Loops

• Positive Feedback: Increasing levels of estrogen in the follicular phase cause GnRH release, resulting in an LH surge and ovulation

• Negative Feedback: In the luteal phase, a high level of progesterone and estrogen has negative inhibition on GnRH, FSH and LH to ensure no other follicles mature.

Common Ovarian Disorders

Common ovarian disorders include ovarian cysts, polycystic ovary syndrome (PCOS), and ovarian cancer. These conditions can affect hormonal balance, fertility, and cause symptoms like irregular periods, pelvic pain, or hormonal imbalances.

Polycystic Ovary Syndrome (PCOS)

The details of the disorder are given below:

Symptoms

• Irregular menstrual cycles

• Acne and oily skin

• Weight gain and inability to lose weight

• Infertility

Causes

• Hormonal imbalance (hyperandrogens)

• Insulin resistance

• Genetic

Treatment

• Diet and exercise

• Medicines to treat irregular menses (oral contraceptive pills)

Ovarian Cysts

The details of the disorder are given below:

Types

• Functional cysts (follicular cysts, corpus luteum cysts)

• Pathological cysts (dermoid cysts, endometriomas, cystadenomas)

Symptoms

• Pelvic pain

• Bloating and abdominal discomfort

• Pain during intercourse

• Irregular menstrual cycles

Management

• Watchful waiting (monitoring small, asymptomatic cysts)

• Medications (hormonal contraceptives to prevent future cysts)

• Surgery (laparoscopy or laparotomy for large or persistent cysts)

Ovarian Cancer

The details of the disorder are given below:

Risk Factors

• Age (most common in women over 50)

• Family history of ovarian or breast cancer

• Genetic mutations (BRCA1 and BRCA2)

• Hormone replacement therapy

• Endometriosis

Symptoms

• Abdominal bloating or swelling

• Pelvic pain

• Difficulty eating or feeling full quickly

• Urinary symptoms (urgency or frequency)

Diagnosis

• Pelvic examination

• Imaging tests (ultrasound, CT scan)

• Blood tests (CA-125)

• Biopsy and histopathological analysis

MCQs on Female Reproductive System - Ovary

Q1. Corpus luteum secretes a hormone called

Option 1: Prolactin

Option 2: Progesterone

Option 3: Aldosterone

Option 4: Testosterone

Correct answer: (2) Progesterone.

Explanation:

The hormone estrogen is released into the bloodstream by follicular cells, which function as endocrine cells.
Conical, yellowish cells called corpus luteum, which degenerate into corpus albicans, are another component of the ovary's cortex.
Progesterone, estrogen, and relaxin are secreted by the corpus luteum, which also serves as an endocrine cell.

The Corpus luteum functions as endocrine cells and secretes progesterone, estradiol, and relaxin.

Hence, the correct answer is the option (2) Progesterone.

Q2. Primary follicles covered with ___ cells are called secondary follicles.

Option 1: Granulosa cells

Option 2: Theca

Option 3: Both a & b

Option 4: None of the above

Correct answer: (3) Both a & b.

Explanation:

The development of oocytes in females begins with the oogonium, which starts division but gets arrested at prophase I of meiosis, resulting in the formation of a primary oocyte. This primary oocyte is surrounded by a single layer of granulosa cells, forming the primary follicle. As the oocyte matures, the primary follicle is further surrounded by more granulosa cells, and a new layer called the theca forms around it. This combination of the oocyte, granulosa cells, and theca layer is referred to as the secondary follicle. The secondary follicle is a more advanced stage, offering protection and support for the developing oocyte, preparing it for potential maturation and ovulation.

Hence, the correct answer is option (3) Both a & b.

Q3. Gamete mother cells in females are known as?

Option 1: Spermatogonia

Option 2: Oogonium

Option 3: Both a & b

Option 4: None of the above

Correct answer: (2) Oogonium.

Explanation:

Gamete mother cells in females are termed oogonia. These cells, located in the ovaries, are crucial for the creation of female gametes, also known as egg cells or ova. They are diploid and undergo oogenesis.

Key Notes:

1. Definition: Oogonia are precursor cells in female ovaries, responsible for producing gametes via oogenesis.
2. Location: Found in ovaries during early development, especially fetal stages in mammals.
3. Development: Oogonia multiply through mitosis during fetal growth. Some transform into primary oocytes, initiating meiosis but halting at prophase I until puberty.
4. Function: Oogonia are vital for forming ova, which are later released during ovulation.

Hence, the correct answer is option (2) Oogonium.

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