Male Reproductive System and Testosterone
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Questions and Answers

What is the primary function of the arterio-venous exchange (counter-current exchange) in the testes?

  • To regulate blood pressure within the testicular artery.
  • To re-circulate testosterone and regulate testicular temperature. (correct)
  • To remove waste products from the interstitial cells.
  • To facilitate the transport of nutrients to the seminiferous tubules.

How does the relaxation of the dartos muscle in the scrotum contribute to thermoregulation?

  • It decreases scrotal size, reducing the surface area for heat loss.
  • It increases wrinkling, trapping heat within the scrotum.
  • It constricts blood vessels, reducing blood flow to the testes.
  • It increases scrotal size, increasing the surface area for heat loss. (correct)

Which of the following is an anabolic effect of testosterone?

  • Decreased red blood cell production.
  • Increased bone mineralization. (correct)
  • Decreased sebaceous gland secretion.
  • Increased deposition of subcutaneous fat.

How does testosterone influence lipid profiles and cardiovascular health?

<p>It increases LDL and decreases HDL, increasing cardiovascular risk. (B)</p> Signup and view all the answers

Besides the testes, where else is testosterone primarily synthesized in males?

<p>Adrenal cortex (A)</p> Signup and view all the answers

Which cells within the testes are responsible for the production of testosterone?

<p>Interstitial cells (Leydig cells) (A)</p> Signup and view all the answers

Which of the following physiological responses is NOT directly facilitated by androgens such as testosterone?

<p>Deposition of subcutaneous fat on the hips and thighs (A)</p> Signup and view all the answers

What is the role of erythropoietin in relation to testosterone's anabolic effects?

<p>Stimulating red blood cell production. (D)</p> Signup and view all the answers

What is the primary function of Leydig cells within the testes?

<p>To secrete testosterone, a male steroid hormone (D)</p> Signup and view all the answers

Which of the following is NOT a direct effect of testosterone secretion at puberty?

<p>Increased production of follicle-stimulating hormone (FSH) (B)</p> Signup and view all the answers

What role do Sertoli cells play in spermatogenesis?

<p>Secreting inhibin to regulate FSH levels and nourishing developing sperm (B)</p> Signup and view all the answers

How do testosterone and inhibin regulate the Hypothalamic-Pituitary-Gonadal (HPG) axis?

<p>By inhibiting the hypothalamus and/or pituitary gland (D)</p> Signup and view all the answers

What is the role of gonadotropin-releasing hormone (GnRH) in the male reproductive system?

<p>Controls the release of LH and FSH from the anterior pituitary (A)</p> Signup and view all the answers

If a male patient has a tumor that causes excessive inhibin secretion, what would be the likely effect on his hormone levels?

<p>Decreased FSH secretion (D)</p> Signup and view all the answers

Where does the maturation and storage of sperm cells primarily occur after they are produced in the seminiferous tubules?

<p>Epididymis (A)</p> Signup and view all the answers

A researcher is studying the effects of a drug that selectively blocks the action of LH. What direct effect would be expected in male subjects?

<p>Decreased testosterone production by Leydig cells (C)</p> Signup and view all the answers

Which of the following best describes the primary mechanism by which the hypothalamus controls the anterior pituitary gland?

<p>Secretion of releasing and inhibitory hormones into the hypothalamo-hypophyseal portal system. (C)</p> Signup and view all the answers

A researcher is investigating a new drug that selectively inhibits the enzyme aromatase in the testes. What effect would this drug likely have on testosterone levels and spermatogenesis?

<p>Increased testosterone levels and impaired spermatogenesis. (D)</p> Signup and view all the answers

What is required for normal spermatogenesis?

<p>High intratesticular testosterone, FSH, and lower testis temperature. (C)</p> Signup and view all the answers

If the hypothalamus is damaged, which of the following hormonal changes would you expect to observe?

<p>Decreased secretion of releasing and inhibitory hormones. (C)</p> Signup and view all the answers

A patient is diagnosed with a condition causing significantly elevated levels of inhibin. How would this likely affect the hypothalamic-pituitary-testicular axis?

<p>Decreased GnRH secretion and reduced spermatogenesis. (D)</p> Signup and view all the answers

Which of the following is the correct sequence of hormonal control in the male reproductive system, starting from the hypothalamus?

<p>GnRH → LH → Testosterone → Sperm production (D)</p> Signup and view all the answers

A man is experiencing infertility due to a genetic defect that impairs the function of Sertoli cells. How does this condition primarily affect his fertility?

<p>Impaired sperm maturation and nourishment. (C)</p> Signup and view all the answers

Why is lower testis temperature essential for normal spermatogenesis?

<p>To optimize enzymatic activity involved in sperm production. (B)</p> Signup and view all the answers

During spermatogenesis, which cells are the first to become haploid?

<p>Secondary spermatocytes (A)</p> Signup and view all the answers

What cellular process accurately describes spermiogenesis?

<p>The conversion of spermatids to spermatozoa. (C)</p> Signup and view all the answers

How do the dartos and cremaster muscles work to regulate testicular temperature?

<p>Maintain proper temperature for sperm storage and development (B)</p> Signup and view all the answers

Which combination of hormones is essential for facilitating spermatogenesis?

<p>Gonadotropin releasing hormone (GnRH) &amp; Testosterone (B)</p> Signup and view all the answers

Which hormone is primarily responsible for the development of secondary sex characteristics in males?

<p>Testosterone (A)</p> Signup and view all the answers

Which hormone directly stimulates the release of testosterone from Leydig cells?

<p>Luteinizing hormone (B)</p> Signup and view all the answers

Which type of cells are the primary responders to testosterone within the testes, supporting spermatogenesis?

<p>Sertoli cells (D)</p> Signup and view all the answers

Which of the following is NOT considered an anabolic effect of testosterone?

<p>Broader shoulder and narrower hip (A)</p> Signup and view all the answers

What is the primary role of Follicle Stimulating Hormone (FSH) in male reproductive function, in conjunction with high intratesticular testosterone?

<p>Supporting normal spermatogenesis. (C)</p> Signup and view all the answers

Which of the following mechanisms is most critical for maintaining optimal spermatogenesis within the testes?

<p>High intratesticular testosterone concentration and lower testis temperature. (C)</p> Signup and view all the answers

How does the hypothalamic-pituitary-testicular axis primarily regulate testosterone production?

<p>Through negative feedback, where high testosterone levels inhibit GnRH and LH secretion. (A)</p> Signup and view all the answers

The anabolic effects of testosterone primarily lead to which physiological change?

<p>Growth and development of muscle mass and bone density. (C)</p> Signup and view all the answers

What is the expected outcome of disrupting the negative feedback loop within the hypothalamic-pituitary-testicular axis?

<p>Uncontrolled fluctuation of testosterone levels due to lack of regulation. (D)</p> Signup and view all the answers

What is the primary function of Sertoli cells within the seminiferous tubules?

<p>Secreting testicular fluid and androgen-binding protein (ABP) to support spermatogenesis. (A)</p> Signup and view all the answers

Which of the following best describes the role of LH (Luteinizing Hormone) in spermatogenesis?

<p>Stimulates Leydig cells to secrete testosterone. (A)</p> Signup and view all the answers

How does androgen-binding protein (ABP) contribute to spermatogenesis?

<p>It binds to testosterone, maintaining a high concentration within the testes. (B)</p> Signup and view all the answers

What is the ploidy of a primary spermatocyte?

<p>Diploid (2n) (C)</p> Signup and view all the answers

The process of spermiogenesis involves:

<p>The differentiation of spermatids into spermatozoa. (A)</p> Signup and view all the answers

How many chromosomes are present in a human spermatid?

<p>23 (C)</p> Signup and view all the answers

Which of the following sequences represents the correct order of cell types during spermatogenesis?

<p>Spermatogonium → Primary Spermatocyte → Secondary Spermatocyte → Spermatid → Spermatozoa (A)</p> Signup and view all the answers

What is the duration of the entire spermatogenesis process in humans?

<p>64-72 days (B)</p> Signup and view all the answers

What is the role of GnRH (Gonadotropin-releasing hormone) in the hormonal control of spermatogenesis?

<p>Stimulates the anterior pituitary to release FSH and LH. (A)</p> Signup and view all the answers

A researcher is studying a cell from the seminiferous tubules and observes that it contains 23 chromosomes, each with a pair of duplicate chromatids. This cell is most likely a:

<p>Secondary spermatocyte (D)</p> Signup and view all the answers

Which of the following is an endocrine function of the testes?

<p>Secretion of testosterone (B)</p> Signup and view all the answers

Spermatogonia undergo mitosis to produce which two cell types?

<p>Type A cell and Type B cell (B)</p> Signup and view all the answers

If a disruption occurred during meiosis I, preventing the proper separation of homologous chromosomes, what would be the most likely outcome?

<p>Secondary spermatocytes would have an abnormal number of chromosomes. (A)</p> Signup and view all the answers

A male patient has a mutation that impairs the function of Sertoli cells. Which of the following would be a likely consequence of this mutation?

<p>Impaired spermatogenesis (B)</p> Signup and view all the answers

During spermatogenesis, at what stage does a cell transition from diploid to haploid?

<p>End of Meiosis I (D)</p> Signup and view all the answers

Flashcards

HPG Axis

Axis involving hypothalamus, pituitary gland, and gonads (testes).

Seminiferous Tubules

Tightly packed structures within the testes where sperm formation occurs.

Leydig Cells

Cells between seminiferous tubules that secrete testosterone.

Sertoli Cells

Cells within the seminiferous tubules that secrete inhibin and feed sperm cells.

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Testosterone (T)

Male steroid hormone secreted by Leydig cells, crucial for male development and function.

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Inhibin

Peptide hormone secreted by Sertoli cells that inhibits FSH secretion.

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LH and FSH

Tropic hormones (LH and FSH) stimulate testicular function.

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Spermatogenesis

The process of sperm cell development within the testes.

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Hormone

A chemical substance secreted in small amounts from an endocrine gland directly into the bloodstream, causing physiological responses at target tissues.

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Hypothalamus' control of the anterior pituitary

The hypothalamus controls the anterior pituitary by secreting releasing and inhibitory hormones into the hypothalamo-hypophyseal portal system.

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Hypothalamic-Pituitary-Testicular Axis

A regulatory system involving the hypothalamus, pituitary gland, and testes that controls male reproductive functions.

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Testicular Steroidogenesis

The synthesis of steroid hormones, like testosterone, in the testes.

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Conversion of Testosterone (T)

Testosterone is converted into other hormones with various effects within the body.

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Hormonal Support for Spermatogenesis

High levels of testosterone within the testes and FSH are necessary for normal sperm production.

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Androgenic and Anabolic Effects of Testosterone

Testosterone has effects that promote male characteristics and muscle growth.

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Counter-current exchange (testosterone)

Recirculation of testosterone via exchange between spermatic arteries and systemic veins.

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Testicular Temperature Regulation

Keeps the testes cooler than body temperature for spermatogenesis.

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Dartos Muscle

Muscle relaxation leads to increased scrotal surface area to promote heat loss.

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Cremaster Muscle

Muscle relaxation allows the scrotum to descend further from the body core, promoting cooling.

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Anabolic effects of Testosterone

Promotes bone and muscle growth.

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Testosterone & Red Blood Cells

Increase in red blood cell production via erythropoietin stimulation.

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Androgenic effects of Testosterone

Development of reproductive organs, increased hair growth, broader shoulders, and narrower hips.

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Interstitial cells

Cells in the testes that secrete testosterone.

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Testosterone Conversion

Testosterone is converted to dihydrotestosterone (DHT) or estradiol, influencing different physiological effects.

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Hormonal Support & Temperature

High intratesticular testosterone and FSH are necessary; lower testis temperature is crucial for normal sperm development.

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Spermatids

Haploid cells formed during spermatogenesis.

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Dartos and cremaster muscle function

To maintain proper temperature for sperm storage and development.

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Hormones facilitating spermatogenesis

Follicle-stimulating hormone (FSH), Gonadotropin releasing hormone(GnRH), and Testosterone

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Secondary sex characteristics in males

The development of male characteristics such as facial hair and muscle growth.

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Hormone involved in testosterone release

Luteinizing hormone

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Anabolic effects of testosterone EXCEPT

Increased growth in bone

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Spermatogonium

Immature male gamete.

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Spermatozoa

Mature male gamete.

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Primary Spermatocyte

Diploid cell that undergoes meiosis I in spermatogenesis.

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Secondary Spermatocyte

Haploid cell resulting from meiosis I, which then undergoes meiosis II.

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Sex Chromosome

Determines sex. XX = Female, XY = Male.

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Testicular fluid

A transport medium for sperm

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Androgen Binding Protein (ABP)

Binds testosterone to maintain high concentration for spermatogenesis.

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Follicle-Stimulating Hormone (FSH)

Hormone that stimulates Sertoli cells to produce ABP.

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Luteinizing Hormone (LH)

Hormone that stimulates Leydig cells to produce testosterone.

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Gonadotropin-Releasing Hormone (GnRH)

Hormone that stimulates the release of FSH and LH.

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Study Notes

  • This lecture discusses male production within the context of a Master of Nursing Science (Pre-registration) Programme, NURS6210 Physiology II, for Year 1 Term 2.
  • The lecture date is set for Jan 10, 2025 (Friday) from 11:30 to 12:15.

Learning Objectives

  • Understand the hypothalamic-pituitary-testicular axis and its feedback control.
  • Describe the testis and the process of spermatogenesis.
  • Understand testicular steroidogenesis and the conversion of testosterone (T).
  • Understand hormonal support and the importance of lower testis temperature for spermatogenesis, including the roles of high intratesticular testosterone and Follicle Stimulating Hormone (FSH).
  • Understand the androgenic and anabolic effects of testosterone.

Hormones

  • Hormones are chemical substances secreted in small amounts from an endocrine gland.
  • They go directly into the bloodstream in response to a stimulus.
  • Hormones cause physiological responses at target tissues.

Hypothalamus and Pituitary Control

  • The hypothalamus controls the anterior pituitary via hypothalamic-releasing and hypothalamic-inhibitory hormones.
  • These hormones enter the primary capillary plexus of the hypothalamo-hypophyseal portal system.
  • They travel through portal veins to act on specific receptors on different pituitary cells.
  • This causes the pituitary cells to secrete their respective hormones.

Hypothalamic-Pituitary-Gonadal (HPG) Axis

  • The male testis consists of tightly packed seminiferous tubules.
  • Sperm formation (spermatogenesis) occurs within these tubules.
  • Leydig cells between the tubules secrete testosterone (T).
  • Sertoli cells secrete inhibin, a peptide hormone, and feed the maturing sperm.
  • Secretion of testosterone (T) starts at puberty and initiates spermatogenesis.
  • It induces the development of male accessory organs, stimulates protein synthesis, induces male secondary sexual characteristics, and increases sex drive.
  • Testicular function is stimulated by luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the anterior pituitary.
  • These tropic hormones are under hypothalamic control via pulsatile release of gonadotropin-releasing hormone (GnRH).
  • Testosterone (T) and inhibin inhibit the hypothalamus and/or the pituitary glands.

Hormones in Male Reproductive System

  • Gonadotropin-releasing hormone (GnRH) is released by the hypothalamus.
  • The anterior pituitary releases gonadotropic hormones: FSH and LH.
  • FSH stimulates spermatogenesis in Sertoli cells
  • LH stimulates androgen (testosterone) secretion in Leydig cells.
  • Testosterone affects primary and secondary sexual characteristics.

Male Reproductive Hormones Control

  • GnRH, released from the hypothalamus, controls the pituitary gland, which in turn has a negative feedback effect on the hypothalamus.
  • FSH stimulates the testes.
  • LH is a luteinizing hormone.

Spermatogenesis

  • Spermatogenesis is the origin and development of sperm cells within the testes.
  • Sperm cells are produced within the seminiferous tubules, located in the testes.
  • Mature sperm are transported through the seminiferous tubules and stored in the epididymis for maturation.
  • Spermatogenesis is a process where spermatogonia develop into spermatozoa and takes 64 to 72 days.
  • Mitosis of spermatogonium takes 16 days.
  • Each spermatogonium produces two daughter cells.
  • One remains and the basement membrane, the other becomes a primary spermatocyte.
  • Meiosis I takes 24 days.
  • The primary spermatocyte becomes two secondary spermatocytes.
  • The end result of meiosis II is 4 haploid spermatids, each containing 23 chromosomes.
  • Each Spermatid matures into a single spermatozoon.
  • Humans have 23 pairs of chromosomes; the 23rd pair determines sex (X/Y for male, X/X for female).

Testes Functions

  • Sertoli cells support spermatogenesis and secrete testicular fluid and androgen-binding protein (ABP).
  • Leydig cells secrete testosterone, which can convert to dihydrotestosterone (DHT) or estradiol.
  • FSH stimulates an increase in production of adrogen binding protein.
  • LH facilitates the production of testosterone.

Hormonal Control of Spermatogenesis

  • Hypothalamus releases Gonadotropin releasing hormone
  • GnRH causes the Anterior pituitary to release FSH and LH
  • FSH and LH act of the Testes
  • Sertoli cells produce Androgen binding protein
  • Leydig cells produce Testosterone
  • These become DHT and Estradiol

Local Testosterone Levels

  • Leydig cells, which secrete testosterone, are located near seminiferous tubules.
  • Androgen binding protein (ABP) helps maintain high concentration of testosterone within the testes, which is essential for spermatogenesis.
  • Re-circulation of testosterone occurs through counter-current arterio-venous exchange.

Testicular Temperature

  • Normal spermatogenesis requires a lower temperature of 33-34°C.
  • During fetal development, the testes undergo testicular descent to move away from the body's core.
  • Arterio-venous exchange helps maintain the temperature.
  • Dartos muscle relaxes, increasing scrotal size, and therefore surface area, for heat loss

Other effects of Testosterone & Dihydrotestosterone

  • Anabolic effects:
    • Increases growth in bone (↑ mineralization).
    • Increases muscle (↑ protein formation).
    • Increases red blood cells.
    • Increases sebaceous gland secretion leading to acne.
    • Increases Low-density lipoprotein (LDL), but decreases High-density lipoprotein (HDL), increasing cardiovascular disease risk.
  • Androgenic effects:
    • Increases sex drive/libido.
    • Develops reproductive organs.
    • Increases hair in pubic, axillary & facial areas.
    • Broader shoulder and narrower hip.

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NURS6210 Physiology II - Male Reproduction Lecture Slides (PDF)

Description

Explore the male reproductive system, focusing on the roles of arterio-venous exchange, dartos muscle relaxation, and testosterone's anabolic effects. Investigate testosterone's influence on lipid profiles, synthesis locations, and Leydig cell function. Also, understand how testosterone and inhibin regulate the HPG axis.

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