Figure 1. Organ Anatomy by Structural Resolution.

Organ complexity can be arranged into 4 primary structural resolutions, macrostructure, mesostructure, microstructure, and nanostructure. As an example, the kidney macrostructurally (resolution >1cm), is an organ with three major tubular structures connecting to the body’s vascular supply and renal network. Mesostructural elements (1mm-1cm) help transport key products to and from the functional kidney units. On the microstructural level (1μm-1mm) are a network of complex structures that make up the kidney’s functional unit: the nephron made up of the proximal and distal convoluted tubules, the loop of Henle, and the collecting duct. Finally, the kidney nanostructure (1nm -1μm), can be characterized, with its unique extracellular matrix (ECM) components, diffusion channels, and enzymes (the SEM image is reprinted under creative commons license from reference¹⁵. Copyright 2018, Springer Nature).