In a couple with infertility, with normal semen but markedly low fructose, which male reproductive structure is likely deficient?

• A. Bulbourethral glands
• B. Prostate
• C. Adenohypophysis
• D. Seminal vesicles

Answer: (D)

The key idea is that the seminal vesicles supply most of the fructose-rich fluid in semen, which provides an essential energy source for sperm to move. When semen appears normal but fructose is markedly low, it points to a problem with the seminal vesicles or their secretions. Without adequate seminal vesicle fluid, sperm have less available fuel, impairing motility and contributing to infertility.

The prostate and bulbourethral glands contribute other components to semen (like citrate and mucus, respectively) but are not the primary source of fructose. The adenohypophysis controls hormones that regulate testicular function, but a deficiency there wouldn’t specifically cause low semen fructose in an otherwise normal semen sample.