genital tubercle
Summary
The genital tubercle is an embryonic structure that appears around week 4 of gestation and gives rise to external genitalia in both males and females. It differentiates into the penis/clitoris under hormonal influence, with testosterone/DHT promoting male development and absence of these hormones leading to female development.
Detail
The genital tubercle is a small protrusion that develops from the ventral aspect of the cloacal membrane during the 4th week of embryogenesis. It consists of mesenchymal tissue covered by ectoderm and contains the corpus cavernosum primordia. Under the influence of testosterone (converted to dihydrotestosterone by 5α-reductase), the genital tubercle elongates to form the penis, with the urethral folds fusing to create the penile urethra. In the absence of androgens (typical female development), the tubercle remains small and develops into the clitoris, while the urethral folds remain unfused, forming the labia minora. The tubercle is part of the broader external genitalia development that also involves the labioscrotal swellings (future scrotum/labia majora). Disruptions in this process can lead to ambiguous genitalia, hypospadias, or other disorders of sexual development. The timing is critical - masculinization must occur between weeks 8-12 of gestation for normal male external genital development.
Sources
- Langman's Medical Embryology
- Moore's The Developing Human
- First Aid for the USMLE Step 1
- Williams Textbook of Endocrinology
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