Functional tissue units (FTUs) form the fundamental building blocks of human organs, serving as pivotal components for modeling the body's healthy physiological functions as well as the changes occurring during various disease states. A comprehensive study recently cataloged 22 anatomically based FTUs from ten healthy human organs as part of the Human Reference Atlas (HRA) project, which aims to create detailed maps of the human body at the cellular level.
The research, involving numerous experts and institutions, has provided definitions, dimensions, blood vessel connections, and cellular compositions of these FTUs. The HRA, which consists of 17 consortia, is dedicated to creating freely available maps of the healthy human anatomy. At the highest level of organization, human anatomy is partitioned down from organ systems to tissues, and finally to functional tissue units.
According to the researchers, FTUs are defined as “a three-dimensional block of cells centered around a capillary, such as each cell within this block being within diffusion distance from any other.” The updated definition allows for the incorporation of nested FTUs, highlighting the complexity of organ function whereby multiple FTUs collaborate for overall efficiency. This hierarchical organization is exemplified by the kidney nephron, which comprises smaller FTUs working together for renal filtration.
Indeed, the catalog presents 22 FTUs collected from the kidney, liver, lung, pancreas, spleen, skin, thymus, and more. Each FTU's characteristics, such as size, vascular connections, and types of cells involved, were systematically documented and organized. For example, the kidney nephron is composed of seven distinct FTUs, each contributing independently yet integrally to the nephron's overall function.
Healthcare researchers are particularly excited about the HRA initiative because its systematic approach paves the way for significant advancements in the fields of biology and medicine. The catalog allows for cross-comparison between FTUs within various organs, granting scientists insights necessary for enhanced research and education.
The initiative integrates cutting-edge data by using standardized metadata frameworks. All anatomical terms are linked to the multi-species Uber-anatomy Ontology (Uberon), and cellular data aligns with Cell Ontology to promote computational access. Not only does this accessibility facilitate clarity, but it also encourages collaboration between researchers studying distinct areas of human anatomy.
The researchers state, "This research presents the first systematic catalog of FTUs and their vascular connectivity within major organs," emphasizing its unprecedented nature. Enhanced visualizations detailing the geometry and organization of FTUs within different organs are freely available online, helping educators and students alike grasp complex physiological concepts.
Comprehensive datasets, illustrations, and crosswalk tables connecting anatomical structures to their corresponding ontologies equip users to easily navigate and utilize the presented information. Data collected exhibits the cellular diversity within each FTU, and researchers can compare and assess how FTUs function together, potentially influencing drug discovery and disease modeling.
The catalog, which is part of the HRA, has broader educational goals, aiming to provide insight about organ systems and their interactions. The combinations of varied file formats, including vector and easily downloadable formats, allow for educational applications beyond primary anatomical research, such as patient education and public awareness.
Future avenues for research will concentrate on refining the catalog with more detailed anatomical variants and exploring how FTUs fluctuate across different demographics and health conditions. The researchers envision using the catalog as part of competitions to develop algorithms for segmenting FTUs, enabling even more specific analysis as their project continues to evolve.
With its diverse applicability and systematic approach, the FTU catalog from the Human Reference Atlas not only enhances scientific knowledge but also stands as a valuable resource for future endeavors within biological research and education.