Role of Hormones in Human Reproductive System: Functions, Diagrams

Role of Hormones in Human Reproductive System: Hormones are defined as chemical messengers that are produced by cells or tissues of the endocrine system and travel through the blood to act on target cells or target organs. Hormones play an important role in the process of reproduction. Both in the male and female reproductive systems, hormones contribute to developing and maintaining sexual characteristics.

The hormones governing the development and control of reproductive organs and secondary sexual characteristics are called sex hormones. During puberty i.e. between the age of 9-14 years, the release of sex hormones brings sexual maturity in males and females. The sex hormones are produced in the ovaries and testes in females and males respectively. In this article, we will provide information about the role of hormones in human reproductive system supported with diagrams. Continue reading to learn more!

Sex Hormones

The hormone is a chemical messenger that is produced by cells or tissues of the endocrine system and travels through the blood to act on target cells or target organs. The hormones involved in the development and control of reproductive organs and secondary sexual characteristics are called sex hormones. Human males and females start producing sex hormones at the age of puberty (between 9-14 years).

The glands that produce sex hormones are the adrenal glands and ovaries and testes (gonads) respectively in females and males.

Male Sex Hormones

The testes are paired sex organs in males. The interstitial cells found in the areas between the sperm-producing seminiferous tubules produce androgens (a group of male hormones). The principal androgen in human males is testosterone. Besides this, a small amount of testosterone is also produced by the adrenal gland.

Female Sex Hormones

Ovaries are a set of paired glands in the pelvic region that produce several types of female sex hormones. The hormones and their site of secretion in the ovaries are discussed as follows:

• Estrogen: It is a hormone released by the granulosa cells of the ovarian follicles in response to follicle-stimulating hormone (FSH). A small amount of estrogen is also secreted by the adrenal gland.
• Progesterone: It is secreted by the corpus luteum (the tissue left behind after the rupture of a follicle during ovulation). It is secreted in response to the Luteinising Hormone (LH). It is a pregnancy-promoting steroid hormone.
• Relaxin: It is a hormone secreted by the ovaries and placenta. The corpus luteum also secretes a small amount of relaxin in the terminal stages of pregnancy.

Testosterone, human chorionic gonadotropin, and human placental lactogen are other hormones secreted by females.

Role of Hormones: Male Reproductive System

The hormones from the pituitary gland (FSH & LH) stimulate the interstitial cells of the testes to produce testosterone. There are the following reproductive functions of testosterone in males:

• Testosterone stimulates the production of sperms in the seminiferous tubules of the testes.
• Testosterone causes the growth and development of secondary male sex organs at puberty, such as prostate glands, seminal vesicles, and penis.
• Testosterone produces secondary sexual characteristics in boys at puberty, such as enlargement of Adam’s apple, deeper voice, growth of facial hairs, broadening of shoulder and chest, muscular development, etc.
• A balanced secretion of testosterone regulates the sperm count in males.
• Testosterone also stimulates the production of red blood cells in males.

Fig: Functions of Testosterone

Role of Hormones: Female Reproductive System

Functions of Estrogen
The hormones from the pituitary gland stimulate ovaries to release estrogen at the onset of puberty in girls. The reproductive functions performed by the estrogen are as follows:

• Estrogen hormone causes the growth and development of primary female sex organs called ovaries at puberty.
• Estrogens stimulate the development and maintenance of secondary sexual characteristics in females, such as high pitched voice, broadening of hips, development of breasts, etc.
• Estrogen hormone, together with the gonadotropic hormones (FSH and LH) of the anterior pituitary gland, regulates the menstrual cycle.
• Estrogen causes the proliferation (growth) of the endometrium (uterus lining) to replace the layer lost during previous menstruation.
• Estrogen hormone maintains the thickness of the vaginal wall and lubrication of the vagina.

Fig: Functions of Estrogen

Functions of Progesterone
Progesterone is a steroid hormone. The production of progesterone in the corpus luteum is stimulated by the Luteinising Hormone. Progesterone contributes to the following functions during the reproductive cycle in females:

• Progesterone inhibits the secretion of Follicular Stimulating Hormone (FSH) and hence stops the further follicles from developing. In this way, this hormone stabilises the menstrual cycle and prepares the body for pregnancy.
• Progesterone causes the blood vessels to grow into the endometrium and contribute to the thickening of the persisting uterine wall. This thickened lining facilitates the implantation of the embryo and provides nutrients to the developing embryo through the placenta.

Fig: Functions of Progesterone

Functions of Relaxin
Relaxin hormone is produced by the ovaries. The placenta produces relaxin hormone during pregnancy.

1. The Relaxin hormone relaxes the pubic ligaments and dilates the cervix to facilitate parturition.
2. It prepares the uterus for the action of oxytocin during labour.

Besides these, some other sex hormones are produced in small quantities in females that perform the following reproductive functions:

• Testosterone is found in small amounts in females and affects fertility, menstruation, and red blood cell production in females. High level of testosterone in females causes the growth of facial hairs and irregular menstrual cycles. In severe conditions, it may cause infertility in females.
• Human chorionic gonadotropin (hCG) is a hormone that is produced by the placenta during pregnancy. It stimulates the progesterone released from the corpus luteum and maintains the level of progesterone in females throughout the gestation period.
• Human placental lactogen is a polypeptide hormone secreted by the placenta that enters the maternal circulation and disappears immediately after delivery. It stimulates the growth of mammary glands.

Role of Luteinizing Hormone in Menstrual Cycle

The five hormones regulate the menstrual cycle in females. These are Gonadotropin Releasing Hormone (GnRH), Follicle Stimulating Hormone (FSH), Luteinising Hormone (LH), estrogens, and progesterone.

• GnRH is released from the hypothalamus and stimulates the release of the FSH and LH from the anterior pituitary.
• FSH causes the ovarian follicle and its eggs to mature, and the maturing follicle synthesises estrogens.
• The threshold level of estrogen triggers the release of LH that stimulates the ovulation and conversion of rupture follicles into the corpus luteum, which synthesises and releases progesterone.
• Estrogen causes the growth of the endometrium to replace the layer lost during previous menstruation.
• Progesterone causes the growth of blood vessels in the endometrium and inhibits the secretion of FSH and LH.

Hormonal Control of Reproductive Systems in Both Male and Female

Hormones of the hypothalamus, pituitary gland, and gonads control the functioning of reproductive systems in males and females.

Hormonal control of Reproductive system in Males

• Hypothalamus secretes Gonadotropin Releasing Hormone (GnRH) to stimulate the pituitary gland to secrete Follicle Stimulating Hormone and Luteinising Hormone (FSH & LH).
• FSH stimulates the Sertoli cells (cells of seminiferous tubules) for spermatogenesis.
• LH stimulates the interstitial cells (lying between the seminiferous tubules) to secrete steroid hormone, testosterone, essential for the development of secondary sexual characters and sperm production.
• Reproductive hormone concentrations are regulated by the negative feedback mechanism. The high concentration of testosterone inhibits the secretion of GnRH from the hypothalamus.
• As a result, the hypothalamus secretes GnIH (Gonadotropin Inhibiting Hormone) that reduces the secretion of FSH and LH from the pituitary.
• Testosterone, if excess, can also directly inhibit the secretion of FSH and LH from the pituitary gland.

In this way, the function of male reproductive systems and secretion of male sex hormones is being regulated.

Fig: Hormonal Control of Male Reproductive System

Hormonal control of Reproductive system in Females

• The mature follicle ruptures to liberate the ovum. This is called ovulation. The stimulus is a surge of Luteinising Hormone secreted by the pituitary gland.
• The granulosa cells of developing ovarian follicles synthesise estrogens, and the corpus luteum synthesises progesterone.
• The synthesis of estrogen is stimulated by Follicle Stimulating Hormone, which is, in turn, controlled by the hypothalamic Gonadotropin Releasing Hormone.
• The high levels of estrogens suppress the release of GnRH, providing negative feedback control of hormone levels.
• On the other hand, progesterone production is stimulated by the Luteinising Hormone, which is also stimulated by hypothalamic GnRH.
• High levels of progesterone also control themselves by the negative feedback loop with progesterone that further inhibits the release of GnRH from the hypothalamus.

In this way, the functioning of the female reproductive system and the secretion of female sex hormones are being regulated.

Fig: Hormonal Control of Female Reproductive System

Summary: Role of Hormones in Reproduction

Hormones are the chemical messengers which coordinate and control the activities of living organisms. Sex hormones are responsible for driving sexual development and sexual reproduction. At the age of puberty, the release of sex hormones brings sexual maturity in males and females. Human males produce a sex hormone named testosterone that controls and regulates the functioning of male reproductive organs and thereby brought sexual maturity to males.

Likewise, in females, estrogen and progesterone primarily control the functioning of female reproductive organs and are responsible for sexual maturity in females. This article covers a detailed study about sex hormones and their functioning.

FAQs on Role of Hormone in Reproduction

Frequently asked questions related to the role of hormones in reproductive functions are listed as follows:

Q.1: What hormones are involved in the female reproductive system?
Ans: Estrogen and progesterone are the two hormones that are primarily involved in the female reproductive system.

Q.2: What are the two main functions of the testis?
Ans: The two main functions of testes are the production of sperms and the production of the male sex hormone called testosterone.

Q.3: What are the roles of hormones in the male reproductive system?
Ans: Follicular Stimulating Hormone, Luteinising Hormone, and testosterone are involved in the reproductive development of males. FSH stimulates sperm production. LH stimulates the production of testosterone which in turn, develops secondary sexual characteristics in males.

Q.4: What is the main function of the human reproductive system?
Ans: The main function of the human reproductive system is to ensure the continuity of life of a species on the Earth by the means of sexual reproduction.

Q.5: What are the two main roles of ovaries?
Ans: The two main functions of ovaries are the production of eggs and the production of female sex hormones namely estrogens and progesterone.

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