Function of circle of Willis.
Nearly 400 years ago, Thomas Willis described the arterial ring at the base of the brain (the circle of Willis, CW) and recognized it as a compensatory system in the case of arterial occlusion. This theory is still accepted. We present several arguments that via negativa should discard the compensatory theory. (1) Current theory is anthropocentric; it ignores other species and their analog structures. (2) Arterial pathologies are diseases of old age, appearing after gene propagation. (3) According to the current theory, evolution has foresight. (4) Its commonness among animals indicates that it is probably a convergent evolutionary structure. (5) It was observed that communicating arteries are too small for effective blood flow, and (6) missing or hypoplastic in the majority of the population. We infer that CW, under physiologic conditions, serves as a passive pressure dissipating system; without considerable blood flow, pressure is transferred from the high to low pressure end, the latter being another arterial component of CW. Pressure gradient exists because pulse wave and blood flow arrive into the skull through different cerebral arteries asynchronously, due to arterial tree asymmetry. Therefore, CW and its communicating arteries protect cerebral artery and blood-brain barrier from hemodynamic stress.
1] Department of Anatomy and Neuroscience, Medical School of J. J. Strossmayer University in Osijek, Osijek, Croatia [2] Department of Radiology, Osijek University Medical Center, Osijek, Croatia.
Zvonimir
Z
Vrselja
Department of Biophysics, Medical Statistics and Medical Informatics, Medical School of J. J. Strossmayer University in Osijek, Osijek, Croatia.
Hrvoje
H
Brkic
Department of Hematology, Osijek University Medical Center, Osijek, Croatia.
Stefan
S
Mrdenovic
Department of Anatomy and Neuroscience, Medical School of J. J. Strossmayer University in Osijek, Osijek, Croatia.
Radivoje
R
Radic
1] Department of Chemistry and Biochemistry, Laboratory for DNA Analysis, Medical School of J. J. Strossmayer University in Osijek, Osijek, Croatia [2] Department of Pathology and Legal Medicine, Osijek University Medical Center, Osijek, Croatia.
Goran
G
Curic
D000818:Animals; D001783:Blood Flow Velocity / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D002941:Circle of Willis / Q000502:physiology*; D015444:Exercise / Q000502:physiology; D006801:Humans; D008833:Microcirculation / Q000502:physiology; D008954:Models, Biological; D063177:Pulse Wave Analysis