Comprehensive healthcare systems are structured across progressive tiers of intervention, commonly including preventative care, primary care, secondary care, tertiary care, quaternary care, and rehabilitative or palliative long-term care. Preventative and primary care form the foundation through community clinics and general practitioners, while secondary and tertiary tiers introduce specialized physicians, advanced surgical suites, and intensive care units. Quaternary care represents the ultimate apex of specialized experimental and rare medical interventions.