This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology and Reproduction, Subject name: Physiology
Masculine or feminine features most directly depend on 
Select and explain. 
A. Amygdala, B. Genetic makeup, C. Hypothalamic outflow, D. Serum testosterone levels
D: Serum testosterone levels
Answer: D: Serum testosterone levels 
Explanation: Ans. d (Serum testosterone levels). (Ref. Ganong, Physiology, 21st ed., 420)TestosteroneSource Testis (Leydig cells), adrenalPotency DHT> testosterone > androstenedioneTargets Skin, prostate, seminal vesicles, epididymis, liver (MH-2000)Functions1.Differentiation of wolffian duct system into internal gonadal structures. 2.Secondary sexual characteristics and growth spurt during puberty. 3.Required normal spermatogenesis. 4.Anabolic effects on muscle size, RBC production 5.Increases libido# Testosterone is converted to DHT by the enzyme 5 a-reductase, which is inhibited by finasteride. FunctionsAndrogen binding protein (ABP)Ensures that testosterone in seminifierous tubule is high.Inhibininhibits FSHTestosteroneDifferentiates male genitalia, has anabolic effects on protein metabolism, maintains gametogenesis, maintains libido, inhibits GnRH, and fuses epiphyseal plates in bone.FSHSertoli cells >> function >> sperm production (spermiogenesis)LHLeydig cell