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Cells, Tissues and Organs
Cells form tissues and organs whose functions depend on constant cooperation across the body.
#Different scales describe the same living body
OpenStax describes body organisation from chemical building blocks through cells, tissues, organs and organ systems to the whole person. Molecules form structures within cells; cells perform the processes on which tissues and organs depend. These levels help organise an explanation, rather than representing separate bodies.
A discussion of a molecule, a cell or an organ is therefore working at a particular scale. Moving between scales helps connect a biological mechanism with the part of the body it affects. This page introduces that vocabulary; it does not interpret a person's scan, laboratory result or tissue sample.
Evidence: OpenStax Anatomy and Physiology 2e: body organisation
#Tissues organise cells for particular functions
OpenStax groups human tissues into four broad types. Epithelial tissue covers surfaces, lines passages and forms some glands. Connective tissue supports and connects body structures. Muscle tissue contracts to produce movement. Nervous tissue carries signals that allow communication between parts of the body.
An organ brings different tissue types together in one structure. Naming an organ does not mean all its cells do the same job. These broad categories are a starting point for learning; they do not classify a personal tissue finding as healthy or diseased.
Evidence: OpenStax Anatomy and Physiology 2e: tissue types / OpenStax Anatomy and Physiology 2e: body organisation
#Organ systems overlap in their work
OpenStax defines an organ system as organs working together to meet major bodily needs. It also notes that assigning an organ to just one system can be imprecise because many organs contribute to more than one. For example, its system overview connects circulation with delivering oxygen and nutrients, and respiration with oxygen supply and carbon dioxide removal.
The body is not a set of isolated boxes. Understanding a system involves its connections with others as well as the structures usually listed under its name. This general account does not identify which organ or system is responsible for an individual's symptoms.
Evidence: OpenStax Anatomy and Physiology 2e: body organisation
Source note
The sections above were checked against the linked sources. No clinical review has been performed. This is general research education, not a clinical guideline.