Testosterone

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Flashcards

Testosterone

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Questions

USMLE® Step 1 style questions USMLE

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A researcher studies the development of the male genitalia in utero. Which of the following hormones is directly responsible for the differentiation of the epididymis during the intrauterine period?  

External References

First Aid

2024

2023

2022

2021

Burns

testosterone/methyltestosterone for p. 675

5 α-reductase

testosterone conversion p. 646

Hypogonadism

testosterone/methyltestosterone p. 675

Hypothalamus p. 507

exogenous testosterone effect p. 646

Libido

testosterone and p. 646

Luteinizing hormone (LH)

testosterone p. 675

Testosterone p. 646, 676

androgen insensitivity syndrome p. 656

cryptorchidism p. 669

Klinefelter syndrome p. 655

Leydig cell secretion p. 647

pharmacologic control p. 673

Sertoli cells p. 646

SHBG effect on p. 351

signaling pathways for p. 351

spermatogenesis p. 646

Testosterone-secreting tumors p. NaN

Testosterone synthesis p. 195

Transcript

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When someone mentions testosterone, it might conjure up images of a burly alpha male.

That’s because testosterone, the primary male hormone, is an androgen, andro meaning male and gen meaning “to produce”, which means testosterone helps generate the characteristics associated with male sexuality.

The effects of testosterone are first seen in the fetus.

During the first six weeks of development, the reproductive tissues of males and females are identical,

but in week seven, genes in the sex-determining region of the Y chromosome initiate the development of testicles.

Once they form, the fetal testicles secrete testosterone which guides development of the male urogenital tract and external genitalia,

as well as testicular descent through the inguinal canal which happens in the last two months of fetal development.

The fetal ovaries also secrete testosterone but at much lower levels, and this largely explains the differences in fetal development between boys and girls.

In puberty, the hypothalamic-pituitary axis takes center stage in regulating testosterone levels and gonadal function - which are the testes in young men.

The hypothalamus secretes gonadotropin-releasing hormone which moves through the bridge between the hypothalamus and the pituitary gland, called the hypothalamo-hypophyseal portal system, and gets to the anterior lobe of the pituitary.

In response, the anterior pituitary secretes luteinizing hormone and follicle-stimulating hormone - two gonadotropic hormones which get secreted into the blood and reach the gonads.

Leydig cells, slowly turn cholesterol into testosterone through a number of steps, and the first step of this process is stimulated by luteinizing hormone.

Two important intermediate molecules in that process are dehydroepiandrosterone, also called DHEA, and the molecule that it gets converted into - androstenedione.

Summary

Testosterone is the primary male sex hormone and an anabolic steroid. In men, it plays a key role in the development of male reproductive tissue and secondary sexual characteristics. It is produced mainly in the testes and is responsible for several functions, including sexual differentiation during fetal life, and the development of primary sexual characteristics like an enlarged penis and testes, as well as secondary characteristics like a male pattern of hair growth, voice changes, and various anabolic effects.

Sources

  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Biological Actions of Androgens" Endocrine Reviews (1987)
  6. "The benefits and risks of testosterone replacement therapy: a review" Therapeutics and Clinical Risk Management (2009)
  7. "Testosterone, Bone and Osteoporosis" Frontiers of Hormone Research (2008)
Elsevier

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