The Evolution of the Suspensory System of the Liver: A Narrative Review
Authors: Arnould Beryl , Taylor Hannah , Décarie Pascale , Venne Gabriel 
Published: May 2022

Introduction & Objective

It is known that the viscera in the body of vertebrates participate in the major vital functions of the body, however the role of visceral mobility in the proper functioning of the musculoskeletal system remains insufficiently investigated. In order to understand the potential influence of viscera on the musculoskeletal system, we need to clarify how the suspensory system of viscera has evolved within the outer body of species at different evolutionary timepoints. More importantly, we need to determine how the suspensory system of high‐density organs, which are more prone to influencing the outer body due to their mass, adapted to different types of locomotion. This narrative review was undertaken to reconstruct the theoretical evolution of the liver and related peritoneal ligaments, to investigate its adaptation to bipedal locomotion.

Materials & Methods

The primary focus of this review was the evolution of the peritoneal suspensory ligaments of the liver through documented species at specific evolutionary timepoints: annelid, agnathans, gnathostomes and tetrapods (amphibians to quadrupedal and bipedal mammals). Keyword searches in SCOPUS, PubMed, Google Scholar, and McGill Library databases were conducted in addition to manual searches of other relevant journals, textbooks and dissection manuals.

Results

Qualitative studies on the gross anatomy of the liver and the suspensory peritoneal ligaments of species at different evolutionary time points were identified. A theoretical timeline of the evolution of the suspensory system of the liver was assembled.

Marine species, which rely on lateral undulation, and terrestrial quadrupeds both possess a highly mobile liver and few reliably seen ligaments of suspension. This is concluded to be due to environmental demands and consequent locomotive requirements, such as running, hopping, and leaping. The human liver, in contrast, is securely attached to the diaphragm and the body walls in the upper right quadrant of the abdominal cavity via consistently present ligaments.

Conclusion

This study suggests that locomotive methods led to the adaptation of ligaments that suspend high‐density organs within the body, such as the liver. Compared to other mammals, the human liver has been securely suspended to the diaphragm via peritoneal ligaments and attached to the body walls in response to two‐legged locomotion.

Significance/Implication

This study provides a theoretical timeline of the evolution of the suspensory system of the liver related to locomotion types. Like the musculoskeletal system, it appears that the visceral suspensory ligaments adapted to the different locomotion types found over the evolutionary timeline. Over time, as species adapted, more numerous ligaments provided further attachment. This adaptation is suggestive of potential mechanical influence between the musculoskeletal system and viscera, or vice‐versa. This raises questions regarding the implication of high‐density organs on some musculoskeletal disorders.

To better understand the potential mechanical influence of the human liver on the musculoskeletal system, the suspensory system of the liver and anatomical variations needs to be clearly described.