Which portion is the narrowest portion of the fallopian tube?

Which portion is the narrowest portion of the fallopian tube?

• A. Isthmus
• B. Interstitial (intramural) portion
• C. Ampulla
• D. Infundibulum

Answer: (B)

The segment being tested is the one that passes through the thick muscular wall of the uterus. The interstitial (intramural) portion runs inside the myometrium and opens into the uterine cavity at the uterotubal junction. Because it is surrounded by a dense layer of uterine muscle, its lumen is the most constricted of all the fallopian-tube segments, making it the narrowest part. In contrast, the ampulla is the widest portion where fertilization typically occurs, the infundibulum is the funnel-shaped end with fimbriae, and the isthmus is near the uterus but not embedded in the thick uterine wall, so it is less constricted than the interstitial portion.

The segment being tested is the one that passes through the thick muscular wall of the uterus. The interstitial (intramural) portion runs inside the myometrium and opens into the uterine cavity at the uterotubal junction. Because it is surrounded by a dense layer of uterine muscle, its lumen is the most constricted of all the fallopian-tube segments, making it the narrowest part.

In contrast, the ampulla is the widest portion where fertilization typically occurs, the infundibulum is the funnel-shaped end with fimbriae, and the isthmus is near the uterus but not embedded in the thick uterine wall, so it is less constricted than the interstitial portion.