Inguinal canal is an oblique passage through the lower part of anterior abdominal wall. It is present in both males and females. In males, it allows structures to pass to and from the testis to the abdomen. In females, it allows the passage of round ligament of uterus from the uterus to labium majus. In addition to the above primary structures, it transmits the ilioinguinal nerve in both males and females.
Structure of inguinal canal:
Inguinal canal is about 1.5 inches long in adults. It extends from deep inguinal ring, downward and medially, to the superficial inguinal ring. The deep inguinal ring is an oval opening in fascia transversalis, while the superficial inguinal ring is a triangular defect in the aponeuorsis of external oblique muscle.
The inguinal canal lies immediately above and parallel to the inguinal ligament. However, in infants, the deep inguinal ring lies almost posterior to the superficial, so that the canal is shorter. As a result of growth in following years, the deep inguinal ring moves laterally and the canal elongates.
Walls of inguinal canal:
- Anterior wall: The anterior wall is formed along its entire length by the aponeuorsis of external oblique muscle. In its lateral part, it is reinforced by the origin of internal oblique from the inguinal ligament. No such reinforcement exists in the medial part. Therefore, the anterior wall is strongest in its lateral part. It is important to appreciate that the strongest (lateral) part of the anterior wall lies opposite to the weakest part of the posterior wall.
- Posterior wall: The posterior wall of inguinal canal is formed along its entire length by the fascia transversalis. The medial part of this wall is reinforced by the conjoint tendon (the common tendon of insertion of internal oblique and transversus abdominis). There is no such reinforcement on the lateral side of the wall. Consequently, the posterior wall is strongest in its medial part, which lies opposite the weakest part of the anterior wall.
- Floor of inguinal canal (inferior wall): The floor of the canal is formed by the inguinal ligament. This ligament is in fact the rolled-under inferior edge of aponeuorsis of external oblique muscle. The medial part of this wall is formed by the lacunar ligament.
- Roof of inguinal canal (superior wall): The roof of the canal is formed by the lowest fibers of internal oblique and transversus abdominis muscles.
Functions of inguinal canal:
- In males, the inguinal canal allows structures of the spermatic cord to pass to and from the testis to the abdomen. This allows the testes to leave the abdominal cavity. The importance of this phenomenon can be appreciated by reminding the fact that spermatogenesis takes place only if the testes leave the abdominal cavity to go to a cooler environment in the scrotum.
- In the females, the inguinal canal is smaller as compared to males. It transmits the round ligament of uterus to pass from the uterus to labium majus.
- In both males and females, the inguinal canal also transmits the ilioinguinal nerve.
Inguinal canal as a potential weakness in abdominal wall:
- The presence of inguinal canal in lower part of anterior abdominal wall presents a potential weakness the structure of the wall. However, it is interesting to consider how the design of this canal tries to reduce the weakness.
- The canal is oblique in its form. This causes the weaker parts of it to lie at some distance apart, thus reducing chances of any type of damage.
- The weak inguinal canal can be exploited during forceful activities like coughing, sneezing, straining, parturition, defecation etc. To prevent this, the arching lowest fibers of internal oblique and transversus abdominis muscles contract and flatten out the arched roof so that it is lowered towards the floor. In this condition, the canal is virtually closed.
- In situations where great straining efforts are necessary, the subject naturally tends to assume the squatting position. In this position, the lower part of anterior abdominal wall, containing the inguinal canal, is protected by the thighs.