Ovary: Structure, Hormones and Functions

When we talk about the role of the ovaries in a human female, what is the first thing that comes to your mind? You must be thinking about the production of ovum as we all know of the ovaries to be the primary reproductive organs in human females. Each ovary produces a single ovum in alternate months that serves as the female gamete.

But did you know that the ovaries also function as endocrine glands that pour hormones directly into the blood circulation? 

The changes that girls undergo during puberty, the cyclic changes in the body during every menstrual cycle and the changes experienced by a woman during pregnancy - any idea what influences these major changes in the body? The answer to this lies in the sex hormones such as oestrogen and progesterone that are secreted by the female ovaries. So you can imagine what an important role the ovaries play, not only as gonads but also as endocrine glands, in human females. 

But how do these hormones influence these dramatic changes in the body? Come let us learn more about their roles and functions in this article.

Table of contents

• Structure of ovary
• Hormones of ovary
• Function of ovary
• Practice problems
• FAQs

Structure of Ovary

Females have a pair of ovaries located in the upper-pelvic cavity in the lower abdomen. Each ovary has a point from where blood vessels and nerves enter and exit and this point is known as Hilum. The ovary is connected to the pelvic wall and uterus by ligaments.

Each ovary is composed of an outermost layer known as the germinal epithelium that is formed of simple cuboidal cells. Beneath the germinal epithelium lies the tunica albuginea which is a poorly differentiated capsule of dense fibrous connective tissue. 

Inside tunica albuginea, ovarian stroma is present that encloses two zones. 

• Peripheral cortex-It is a region present inner to the tunica albuginea. It is made up of ovarian follicles surrounded by dense irregular connective tissue with collagen fibres and stromal cells, which are fibroblast-like cells. The cortex is denser in composition and contains both young and mature follicles. It also contains a large mass of yellow cells, known as corpus luteum which is the remnant of a mature Graafian follicle after it has ruptured to release the ovum during ovulation. The degenerating corpus luteum, present as the corpus albicans, is also found in the ovarian cortex.
• Inner medulla - It is a region present inner to the ovarian cortex. The border line between the cortex and medulla is indistinct. Lymphatic vessels, nerves and blood vessels are present in the medulla. It is made up of more loosely structured connective tissue.

Hormones of Ovary

The ovarian or graafian follicles are responsible for the synthesis of oestrogen. The corpus luteum produces a variety of hormones like progesterone, relaxin, inhibin, and activin. Oestrogen and progesterone are steroid hormones.

Oestrogen

Estradiol is the principal oestrogen. Oestrogen stimulates the development of growing ovarian follicles and the maturation of ova in the ovaries. It also regulates the development of mammary glands in females.

It controls female sexual behaviour and also helps in the development of female secondary sexual characters. It helps in growth, development and function of females secondary sex organs such as development of epithelium of the uterus. 

Progesterone

Progesterone is secreted by the corpus luteum of the ovary. It supports pregnancy and stimulates the development of the uterine endometrium. It also acts on the mammary glands and stimulates the milk secretion. 

Relaxin

It is secreted by the corpus luteum during the later stages of pregnancy. It helps to loosen ligaments of the pubic symphysis which in turn helps in widening the cervix during parturition or childbirth.

Inhibin and Activin

Inhibin and activin are secreted by the granulosa cells of the ovary and the corpus luteum. They are antagonistic in function. Inhibin inhibits GnRH (Gonadotropin releasing hormone) production from the hypothalamus which in turn inhibits FSH (Follicle stimulating hormone) production from the anterior lobe of the pituitary gland. 

Activin stimulates the production of GnRH and FSH.

Practice Problems of Ovary

Q1. Which of the following statements is incorrect for ovary:

I) Muscles connect the ovary to the uterus and pelvic wall.

II) Ovary has a stroma with an outer cortex and inner medulla.

III) Each ovary is about 2-4 cm in length.

IV) A thick epithelial covering encloses the stroma of the ovary. 

V) Ovary secretes several steroid hormones.

1. I, IV, and V only
2. I and IV only
3. I, II, and III only
4. IV only

Solution: A pair of ovaries are the main and primary female reproductive organs and the size of each ovary is about 2 to 4 cm in length . Each ovary is connected to the pelvic wall and uterus with the help of ovarian ligaments. The surface of the ovary is covered by the thin layer of germinal epithelium tissue which encloses the internal ovarian stroma which is basically divided into an outer zone named cortex and an inner zone known as medulla.

Thus, statements I and IV are incorrect and the correct option is b.

Q2. In human ovary:

1.  germinal epithelium is absent
2.  tunica albuginea is absent
3. tunica albuginea is present beneath germinal epithelium
4. germinal epithelium is present beneath tunica albuginea 

Solution: The surface of the ovary is covered by the thin layer of germinal epithelium tissue while tunica albuginea is located immediately beneath the germinal epithelium. It is a whitish capsule of the dense irregular connective tissue. Thus, the correct option is c.

Q3. How does relaxin help during child birth?

Answer: Relaxin helps to loosen the ligaments of the pubic symphysis during childbirth. This allows the cervix to soften and dilate to allow passage to the foetus.

Q4. Match the following:

1. A - II, B - I, C - III
2. A - I, B - III, C - II
3. A - III, B - I, C - II
4. A - III, B - II, C - I

Solution: Activin helps to stimulate the release of GnRH (Gonadotropin releasing hormone) from the hypothalamus and FSH (Follicle stimulating hormone) from the anterior lobe of pituitary gland. Inhibin does just the opposite and inhibits the release of FSH and GnRH.

Oestrogen is responsible for the development of growing ovarian follicles and the maturation of ova in the ovaries. It controls female sexual behaviour and also helps in the development of female secondary sexual characters and secondary sex organs such as development of epithelium of the uterus.

Thus, the correct option is c.

FAQs of Ovary

Question1. What does relaxin do in males?

Answer: Relaxin is produced by the prostate gland in males. It stimulates sperm motility and enhances sperm penetration into oocytes.

Question2. Why is progesterone level high during pregnancy?

Answer: In the event of successful fertilisation of the egg and the implantation of the fertilised egg, pregnancy ensues in a human female. This results in persistence of the corpus luteum which does not degenerate and continues to release progesterone in the female body to stimulate the development of the uterine endometrium. Thus, progesterone levels are high during pregnancy.

Question3. What are the consequences of high oestrogen levels in humans?

Answer: If oestrogen levels become high in the body, a human female may suffer from irregular or unusually heavy periods, development of fibroids, perpetual fatigue, etc.

In case of males, it may result in erectile dysfunction (inability to maintain erection), infertility or development of breasts.

Question4. Is activin produced only in human females?

Answer: Activin is produced in both human males and females. The Sertoli cells in the testes of males and the granulosa cells and corpus luteum in the ovaries of females, are responsible for the release of activin in the human body.

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