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UPSC MainsZOOLOGY-PAPER-I202520 Marks
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Q12.

Draw a well-labelled diagram of testis and ovary in mammals, and discuss the functions of their hormones.

How to Approach

The question requires a comprehensive understanding of mammalian reproductive biology. Begin by drawing clear, well-labelled diagrams of both the testis and ovary. Subsequently, discuss the various hormones produced by each gonad, detailing their specific functions in regulating reproductive processes, secondary sexual characteristics, and overall physiological roles. Ensure the answer integrates anatomical structures with hormonal actions for a holistic view, using recent data or relevant examples where appropriate to enhance depth and factual accuracy.

Model Answer

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Introduction

The male and female reproductive systems in mammals are intricately designed organ systems primarily responsible for sexual reproduction, gamete production, and the secretion of vital sex hormones. These hormones play a crucial role in regulating reproductive cycles, influencing secondary sexual characteristics, and maintaining overall physiological homeostasis. The testis in males and the ovary in females are the primary gonads, serving both gametogenic and endocrine functions. Understanding their structure and hormonal contributions is fundamental to comprehending mammalian reproduction and its complexities. This answer will delineate the anatomical features of these organs through diagrams and elaborate on the diverse functions of the hormones they produce.

The mammalian reproductive organs, the testis and the ovary, are crucial for both gamete production and hormone synthesis. Their intricate structures facilitate these vital functions, which are finely regulated by a complex interplay of hormones.

Well-Labelled Diagram of Testis in Mammals

The testis is the primary male gonad, typically located within the scrotum. A transverse section (T.S.) of a mammalian testis reveals its complex internal structure, optimized for spermatogenesis and hormone production.

[Diagram of Testis - An aspirant should draw a clear, well-labelled diagram here. Key labels to include are: Tunica albuginea, Seminiferous tubules, Germinal epithelium, Spermatogonia, Primary spermatocytes, Secondary spermatocytes, Spermatids, Spermatozoa, Sertoli cells, Leydig cells (Interstitial cells), Rete testis, Vasa efferentia, Epididymis (Head, Body, Tail), Blood vessels.]

Description of Key Structures in Testis:

  • Tunica Albuginea: A tough, fibrous capsule surrounding the testis, providing structural support and protection.
  • Seminiferous Tubules: Highly coiled tubes within the testis, lined by germinal epithelium. This is the primary site of spermatogenesis (sperm production).
  • Sertoli Cells (Nurse Cells): Large, pyramid-shaped cells within the seminiferous tubules that provide nourishment to developing sperm, phagocytose residual bodies, and secrete various factors including inhibin and androgen-binding protein (ABP).
  • Leydig Cells (Interstitial Cells): Located in the interstitial spaces between the seminiferous tubules, these cells are responsible for synthesizing and secreting androgens, primarily testosterone.
  • Rete Testis: A network of tubules that collect sperm from the seminiferous tubules.
  • Vasa Efferentia: Ducts that connect the rete testis to the epididymis.
  • Epididymis: A coiled tube located on the posterior aspect of the testis where sperm mature and are stored.

Well-Labelled Diagram of Ovary in Mammals

The ovary is the primary female gonad, typically located in the pelvic cavity. A transverse section (T.S.) of a mammalian ovary shows various stages of follicular development and other associated structures.

[Diagram of Ovary - An aspirant should draw a clear, well-labelled diagram here. Key labels to include are: Germinal epithelium, Tunica albuginea, Ovarian cortex, Ovarian medulla, Primordial follicles, Primary follicles, Secondary follicles, Tertiary/Antral follicles, Graafian follicle, Ovum/Oocyte, Corpus luteum, Corpus albicans, Blood vessels, Nerves.]

Description of Key Structures in Ovary:

  • Germinal Epithelium: An outer layer of cuboidal cells covering the ovarian surface.
  • Tunica Albuginea: A dense connective tissue layer beneath the germinal epithelium.
  • Ovarian Cortex: The outer region containing ovarian follicles at various stages of development.
  • Ovarian Medulla: The inner region composed of loose connective tissue, blood vessels, lymphatics, and nerves.
  • Ovarian Follicles: Structures consisting of an oocyte surrounded by granulosa cells and theca cells, which develop from primordial to mature (Graafian) follicles.
  • Graafian Follicle: A mature follicle that ruptures to release the ovum during ovulation.
  • Corpus Luteum: Formed from the remnants of the ruptured Graafian follicle after ovulation; it secretes progesterone and estrogen.
  • Corpus Albicans: A degenerated corpus luteum if fertilization does not occur.

Functions of Testicular Hormones

The testes secrete several hormones, primarily androgens, which are crucial for male reproductive health and overall physiology. The main hormones are:

Hormone Source Key Functions
Testosterone Leydig cells (Interstitial cells)
  • Spermatogenesis: Essential for the initiation and maintenance of sperm production in the seminiferous tubules.
  • Development of Male Secondary Sexual Characteristics: Promotes growth of facial and body hair, deepening of the voice, increased muscle mass, bone density, and enlargement of male reproductive organs during puberty.
  • Libido and Sexual Function: Regulates sex drive and sexual behavior.
  • Anabolic Effects: Stimulates protein synthesis and muscle growth.
  • Erythropoiesis: Contributes to red blood cell production.
  • Regulation of GnRH and LH/FSH: Exerts negative feedback on the hypothalamus (GnRH) and anterior pituitary (LH/FSH) to regulate its own secretion.
Inhibin Sertoli cells
  • Regulation of FSH: Selectively inhibits the secretion of Follicle-Stimulating Hormone (FSH) from the anterior pituitary, thereby helping to regulate the rate of spermatogenesis.
Androgen-Binding Protein (ABP) Sertoli cells
  • Maintains high testosterone concentration: Binds to testosterone within the seminiferous tubules, maintaining a high local concentration necessary for spermatogenesis, as testosterone is relatively insoluble in water.
Anti-Müllerian Hormone (AMH) Sertoli cells (during fetal development)
  • Sexual Differentiation: In male fetuses, AMH causes the regression of the Müllerian ducts, which would otherwise develop into female reproductive organs.

Functions of Ovarian Hormones

The ovaries are endocrine glands that produce several steroid hormones, mainly estrogens and progestins, which are vital for female reproductive cycles, pregnancy, and secondary sexual characteristics.

Hormone Source Key Functions
Estrogen (primarily Estradiol) Granulosa cells of developing follicles, Corpus luteum
  • Development of Female Secondary Sexual Characteristics: Promotes breast development, widening of hips, and growth of uterine lining during puberty.
  • Menstrual Cycle Regulation: Stimulates the proliferation of the uterine endometrium during the follicular phase, preparing it for potential implantation.
  • Ovulation: High levels of estrogen (specifically estradiol) trigger a positive feedback loop leading to the LH surge, which induces ovulation.
  • Bone Health: Plays a role in maintaining bone density and preventing osteoporosis.
  • Cardiovascular Health: Contributes to cardiovascular protection.
Progesterone Corpus luteum
  • Maintenance of Pregnancy: Essential for maintaining the uterine lining (endometrium) in a secretory phase, making it receptive for implantation and supporting the early stages of pregnancy.
  • Inhibits Uterine Contractions: Relaxes uterine smooth muscle, preventing premature contractions.
  • Mammary Gland Development: Promotes the development of mammary glands in preparation for lactation.
  • Negative Feedback: Inhibits the release of GnRH, LH, and FSH, preventing the development of new follicles during pregnancy and the luteal phase.
Relaxin Corpus luteum (during pregnancy)
  • Facilitates Childbirth: Softens the pubic symphysis and dilates the cervix, aiding in parturition.
Inhibin Granulosa cells
  • Regulation of FSH: Inhibits the secretion of FSH from the anterior pituitary, helping to regulate follicular development.

Conclusion

The mammalian testis and ovary are highly specialized organs that intricately combine gamete production with endocrine functions, forming the cornerstone of sexual reproduction. Their well-defined anatomical structures facilitate complex processes like spermatogenesis and oogenesis, while the hormones they secrete—testosterone and estrogen/progesterone, respectively—orchestrate a wide array of physiological changes. These hormones regulate reproductive cycles, govern the development of secondary sexual characteristics, and are vital for fertility and the maintenance of pregnancy. A balanced interplay of these hormones, under the control of the hypothalamic-pituitary-gonadal axis, is essential for reproductive health and the continuation of species.

Answer Length

This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.

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Additional Resources

Key Definitions

Spermatogenesis
The process by which male primordial germ cells (spermatogonia) develop into mature spermatozoa (sperm) in the seminiferous tubules of the testes. This complex process involves mitotic divisions, meiotic divisions, and spermiogenesis (differentiation of spermatids into spermatozoa).
Oogenesis
The process of formation and maturation of female gametes (ova or eggs) within the ovaries. It begins during fetal development, pauses at puberty, and continues cyclically until menopause, involving meiosis and follicle development.

Key Statistics

Globally, approximately 15% of couples experience infertility, with male factors contributing to 40-50% of cases and female factors to another 40-50%, often linked to hormonal imbalances or structural issues in the gonads. (Source: World Health Organization, 2023)

Source: World Health Organization (WHO)

The average human male produces about 1,500 sperm cells per second (over 100 million per day), highlighting the continuous and high-volume production capacity of the testes under adequate hormonal stimulation. (Source: Human Reproduction Update, 2022)

Source: Human Reproduction Update

Examples

Hormone Replacement Therapy (HRT)

In post-menopausal women, estrogen levels significantly decline, leading to symptoms like hot flashes, bone loss (osteoporosis), and vaginal dryness. Hormone Replacement Therapy (HRT), involving estrogen and sometimes progesterone, is used to alleviate these symptoms and reduce the risk of osteoporosis by replenishing ovarian hormones.

Androgen Deficiency in Aging Males (ADAM)

As men age, testosterone levels can gradually decline, a condition sometimes referred to as 'andropause' or ADAM. Symptoms can include reduced libido, decreased muscle mass, increased body fat, and fatigue. Testosterone replacement therapy can be administered to mitigate these effects, demonstrating the wide-ranging influence of testicular hormones.

Frequently Asked Questions

▶What role do the pituitary hormones play in regulating testicular and ovarian functions?

The anterior pituitary gland secretes Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH). In males, FSH stimulates Sertoli cells for spermatogenesis, while LH stimulates Leydig cells to produce testosterone. In females, FSH promotes follicular growth, and LH triggers ovulation and the formation of the corpus luteum.

▶How do oral contraceptives work to prevent pregnancy?

Oral contraceptives typically contain synthetic forms of estrogen and progesterone. These hormones exert negative feedback on the hypothalamus and pituitary, inhibiting the release of FSH and LH. This prevents follicular development and ovulation, thus preventing pregnancy.

Topics Covered

Human BiologyZoologyReproductive SystemEndocrinologyAnatomy
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