Gonads

Introduction

The male sex glands or gonads are known as testes or testicles; in females, it is known as ovaries. Within some lower invertebrates like hydrozoans, the gonads are temporary, but in higher invertebrates they are permanent. In organisms like worms and leeches, the gonads i.e both male and female gonads are present in a single individual. Usually, there are paired gonads which are responsible for the production of both, hormones and gametes which are necessary for reproduction. But in some species like male lizards, female crocodiles, female bats, etc only one gonad is seen.

Development of gonads

After the process of fertilization in which the fusion or union of male and female gametes, the zygote is formed. This zygote then grows to form a human embryo, but during the growth for the first 2 months of gestation, they are developed identically which means there the embryo is not differentiated into male or female because gonads are not developed yet. During the 4th to 5th week, the gonads initially appear as a pair of longitudinal gonadal or genital ridges. They are termed primitive gonads and are formed from the primordial germ cells that migrate from the yolk sac. These cells, during the sixth week, undergo condensation of the underlying mesenchyme. Until the 7th week of embryo development, the gonads do not acquire male or female morphological characteristics.

Testis

Testis or testicles are the organs of the male reproductive system in animals that are responsible for the production of male reproductive cells, sperms, hormones and androgens.

Structure

The testes are paired, oval-shaped organs that are present within the scrotal sac that is situated in front of the anus and behind the penis. Testes are covered with the fibrous capsule that is known as tunica albuginea. They possess lobules that contain seminiferous tubules, where sperms are produced. These tubules are lined by the Sertoli cells that function in the maturation of spermatozoa. The sperm flows through the rete testes towards the efferent tubules which further transports the sperm to the epididymis for storage as well as maturation. During ejaculation, the sperms are ejected through the epididymis to the urethra and then out from the penis.

Hormones

The major hormone that is synthesized by the testes is testosterone. This synthesis is regulated by the endocrine hormones that are released by the hypothalamus and pituitary. It is essential for the production of sperms.

Functions

• The major function of the testis is in the production and release of sperms.

• These sperms are also stored in the testis.

• They are is also responsible for the secretion of the hormone testosterone.

• The testis is also involved in the synthesis of androgens.

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Diseases

Various diseases related to testicular and scrotal disorders are −

• Epididymitis − It is related to the infection or inflammation of the epididymis that results in swelling of the scrotum or testicles, pain, fever, etc.

• Testicular torsion − It occurs when there is a twist of the spermatic cord or cut off of the blood supply to the testicles. It causes swelling in the testis and scrotum, vomiting, nausea, etc.

• Hypogonadism − It is a condition that results when the testis is unable to produce an efficient amount of testosterone which can lead to infertility, reduced sex drive, erectile dysfunction, etc.

Ovary

The ovary is an essential structure of a female reproductive structure that is responsible for the production of the ovum, hormones required during, fertilization, pregnancy and the development of an embryo.

Structure

The ovaries are paired, solid, oval-shaped glands that are located in the shallow depressions that are called ovarian fossae i.e on either side of the uterus. The outside of the ovary is covered by a layer of simple cuboidal epithelium that is known as the germinal or ovarian epithelium. It consists of multiple developing follicles out of which one eventually matures each month.

Hormones

The hormones that are secreted by the ovaries are estrogen and progesterone. They play a major role during menstruation, pregnancy, embryonic development, etc. Both the hormones are regulated by the pituitary and hypothalamus.

Function

• The ovaries play a major role in both conception and menstruation.

• They are responsible for the production of ova or eggs.

• Ovaries are involved in the synthesis of progesterone and estrogen.

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Diseases

Various diseases related to ovaries are −

• Ovarian cysts − These are small outgrowths that are developed on or inside the ovaries. It leads to pelvic pain, fullness or bloating in the lower belly, pain during menstruation, etc.

• Polycystic ovarian syndrome (PCOS) − It is a common condition that results in hormonal imbalance which causes excess hair growth, acne, infertility and irregular menstrual periods.

• Ovarian cancer − It is a type of uncontrolled growth of cells that are developed in the ovaries. Pain, bloating in the pelvis and abdomen region, loss of appetite, etc are seen during ovarian cancer.

Conclusion

The gonads that are present in both males and females are responsible for the production of male and female reproductive cells respectively. Up to 2 months of gestation the embryo is undistinguishable into male or female but during the 4th to 5th week the gonads start developing. The testis is present within the scrotal sac that is situated in front of the anus and behind the penis. The ovaries are located in the shallow depressions that are called ovarian fossae i.e on either side of the uterus. Various diseases like epididymitis, hypogonadism, etc are seen in testis and PCOS, ovarian cysts, etc are seen in ovaries.

FAQs

Q1. What is the Wolffian duct and what does it give rise to?

Ans. Wolffian duct is a paired structure that is present during embryonic conditions that give rise to the male internal genital structure like seminal vesicle, epididymis, vas deferens and ejaculatory duct.

Q2. What is the Mullerian duct and what does it give rise to?

Ans. Mullerian ducts are paired embryonic structures that give rise to the female reproductive tract including the uterus, oviduct, cervix and upper vagina.

Q3. Name the hormone that is derived from testosterone.

Ans. Dihydrotestosterone is an androgen that is derived from the hormone testosterone and it plays a role in sexual development in males.

Q4. Do females have testosterone, if yes, then who produces it?

Ans. Yes, females do have testosterone and the adrenal glands and ovaries are responsible for the production of testosterone of which the majority is converted into female sex hormone i.e oestradiol.

Q5. Define fertilization and mention the site of fertilization.

Ans. Fertilization is a process that involves the union or fusion of male and female gametes that results in the formation of the zygote. This process takes place in the fallopian tube that links an ovary to the uterus.