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Questions and Answers
What is the primary role of Sertoli cells in the testes?
What is the primary role of Sertoli cells in the testes?
Which hormone is primarily responsible for stimulating testosterone secretion from Leydig cells?
Which hormone is primarily responsible for stimulating testosterone secretion from Leydig cells?
What is the significance of dihydrotestosterone (DHT) in male development?
What is the significance of dihydrotestosterone (DHT) in male development?
How does testosterone affect the hypothalamic-pituitary-gonadal axis?
How does testosterone affect the hypothalamic-pituitary-gonadal axis?
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What role does aromatase play in male physiology?
What role does aromatase play in male physiology?
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What is the main contribution of seminal vesicles to semen?
What is the main contribution of seminal vesicles to semen?
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What is the effect of follicle-stimulating hormone (FSH) in the testes?
What is the effect of follicle-stimulating hormone (FSH) in the testes?
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What is the temperature required for optimal spermatogenesis in the testes?
What is the temperature required for optimal spermatogenesis in the testes?
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Which of the following statements about Sertoli cells is most accurate?
Which of the following statements about Sertoli cells is most accurate?
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What is the primary direct function of dihydrotestosterone (DHT) during puberty?
What is the primary direct function of dihydrotestosterone (DHT) during puberty?
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Which of the following accurately describes the role of testosterone in male reproductive physiology?
Which of the following accurately describes the role of testosterone in male reproductive physiology?
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What is the primary mechanism of the feedback loop involving testosterone in the hypothalamic-pituitary-gonadal axis?
What is the primary mechanism of the feedback loop involving testosterone in the hypothalamic-pituitary-gonadal axis?
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Identify the role of the aromatase enzyme in male physiology.
Identify the role of the aromatase enzyme in male physiology.
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What is the primary source of testosterone in young adult males?
What is the primary source of testosterone in young adult males?
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What is the impact of DHT on male secondary sex characteristics?
What is the impact of DHT on male secondary sex characteristics?
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Which factor is essential for Sertoli cells to initiate and maintain spermatogenesis?
Which factor is essential for Sertoli cells to initiate and maintain spermatogenesis?
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Which of the following accurately represents the secretion pattern of gonadotropin-releasing hormone (GnRH)?
Which of the following accurately represents the secretion pattern of gonadotropin-releasing hormone (GnRH)?
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What contribution do seminal vesicles make to semen volume?
What contribution do seminal vesicles make to semen volume?
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Study Notes
Physiology of Testes
- Testes contain seminiferous tubules lined with Sertoli cells and interstitial Leydig cells.
- Sertoli cells nourish developing sperm and secrete growth factors.
- Sertoli cells create a blood-testis barrier.
- Sertoli cells secrete androgen-binding protein (ABP).
- Leydig cells synthesize and secrete testosterone (T).
- Maintaining a temperature 2°C below body temperature is crucial for spermatogenesis.
- Testosterone production: ~7 mg/day
- Testosterone is mostly bound to albumin and sex hormone-binding globulin (SHBG).
- Cholesterol is converted into pregnenolone.
Endocrine Roles
- Testosterone (T) is produced primarily in the testes.
- Luteinizing hormone (LH) stimulates Leydig cells to produce testosterone.
- Testosterone and follicle-stimulating hormone (FSH) initiate and maintain spermatogenesis.
- Dihydrotestosterone (DHEA) is a more potent form of testosterone created from T.
- DHT is produced by 5-alpha reductase and can be found in skin, prostate, and other genital tissues.
- Aromatase converts testosterone to estradiol (E2) in some tissues.
- These hormones mediate development of male secondary sexual characteristics and spermatogenesis.
Androgen Actions
- Testosterone and DHT bind to intracellular androgen receptors.
- This binding alters transcription, stimulating growth and function of accessory reproductive organs.
- Testosterone promotes development of male internal genitalia, spermatogenesis, muscle mass, and libido.
- DHT contributes to development of external genitalia, prostate enlargement, facial hair, and acne.
Hypothalamic-Pituitary-Gonadal Axis
- Gonadotropin-releasing hormone (GnRH) is released in pulses every 3 hours from the hypothalamus.
- GnRH stimulates the release of LH and FSH from the pituitary.
- LH stimulates Leydig cells to produce testosterone (T).
- FSH stimulates Sertoli cells to support spermatogenesis.
- The production of T and FSH follows a negative feedback loop, where testosterone and inhibin regulate GnRH and LH release.
Ducts and Accessory Glands
- Seminal vesicles contribute about 12 volume units to semen.
- The prostate releases about 20% of semen volume.
- Semen contains sperm, mucus, water, buffers, nutrients (fructose, citric acid, vitamin C, carnitine), enzymes, and zinc.
- Prostaglandins from the seminal vesicles might help with sperm transport or fertilization.
Sperm
- Average sperm concentration is 100 million/mL.
- Low fertility: 20-50 million/mL; infertility: <20 million/mL.
Pathophysiology (e.g., Androgen Insensitivity Syndrome)
- Androgen insensitivity syndrome (AIS) : mutations in the androgen receptor cause XY individuals to present as females, or with ambiguous genitalia.
- Differently mutated androgen receptor forms lead to various clinical presentations.
- Actions of estradiol in males: necessary for fertility, bone density, etc.
Related Conditions
- Hypogonadism: impaired testicular function; categorized into primary (hypergonadotropic), involving reduced T levels with elevated FSH/LH, and secondary (hypogonadotropic).
- Klinefelter syndrome (XXY) is a common example of primary hypogonadism, characterized by reduced testosterone and elevated FSH/LH.
- 5-alpha reductase type 2 deficiency: the body cannot convert testosterone into DHT, can lead to ambiguous genitalia at birth and is often assigned female at birth (but not always).
Prostate Cancer
- Prostate cancer is often related to mutations in the androgen receptor, marked by elevated PSA levels.
- Prostate-specific antigen (PSA) is a marker used to monitor prostate cancer.
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Description
This quiz covers the crucial roles of the testes, focusing on the structure and functions of Sertoli and Leydig cells, as well as testosterone production and its regulation. Examine the endocrine interactions involving luteinizing hormone, follicle-stimulating hormone, and the conversion of testosterone to dihydrotestosterone. Test your knowledge on spermatogenesis and hormonal influences in male physiology.
