The narrowest part of the fallopian tube is the

Appeared in: RRB Staff Nurse Mumbai-2015

Explanation

The fallopian tube is divided into four parts: interstitial, isthmus, ampulla, and infundibulum.
The interstitial portion, also called the intramural part, is the segment that passes through the muscular wall of the uterus.
Due to its location within the dense myometrium, this section is the most constricted and has the narrowest lumen, approximately 1 mm in diameter.
This makes it the narrowest part of the entire fallopian tube.

Option B: The isthmus is a narrow segment of the fallopian tube, but it is located just outside the uterus and is wider than the interstitial portion (approximately 2.5 mm lumen).
Option C: The infundibulum is the funnel-shaped, distal end of the fallopian tube that opens into the peritoneal cavity to catch the egg. It is one of the wider parts, not the narrowest.
Option D: The ampulla is the longest and widest part of the fallopian tube. Its dilated structure is where fertilization most commonly occurs.

Visual 1: Diagram - An illustration of the female reproductive system, clearly labeling the four parts of the fallopian tube (interstitial, isthmus, ampulla, infundibulum) to show their relative positions and sizes from the uterus to the ovary.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Anatomy of the Fallopian Tube as background academic context rather than a clinical decision trigger.
An ectopic pregnancy in the interstitial portion (interstitial pregnancy) is particularly dangerous. Due to the narrowness and high vascularity of the surrounding myometrium, rupture can lead to massive, life-threatening hemorrhage.
Tubal ligation, a permanent method of contraception, is often performed at the isthmus because it is easily accessible and its narrow lumen is simple to block or sever.
What if? If a patient has salpingitis (infection of the fallopian tubes), the narrow interstitial and isthmic portions are most susceptible to blockage from inflammation and scarring, which is a common cause of infertility.

How to Approach the Question

This is a factual recall question based on anatomy.
First, identify the key terms in the question: 'narrowest part' and 'fallopian tube'.
Recall the four anatomical segments of the fallopian tube.
Mentally visualize or sketch the tube's path from the uterus outwards: Interstitial (inside uterine wall) -> Isthmus (narrow part outside uterus) -> Ampulla (wide part) -> Infundibulum (funnel end near ovary).
Based on this structure, deduce that the part passing through the uterine muscle (interstitial) must be the most constricted.
Compare this with the options provided to select the correct answer.

Concept Tested & Keywords

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Practise the full RRB Staff Nurse Mumbai-2015

Attempt every question from this paper in a timed mock, then review the full solution for each one.