How are cells organized into tissues and organs in multicellular organisms?

In multicellular organisms, the organization of cells into tissues and organs is a highly regulated process driven by cell differentiation and intercellular communication.12

From Cells to Tissues

Cells become specialized through a progressive sequence of commitments, often influenced by cytoplasmic determinants and inductive signals from neighboring cells. To form tissues, these specialized cells must recognize and adhere to one another and to the extracellular matrix. This is facilitated by specialized proteins in the plasma membrane and various cell junctions:21

• Adhering junctions: Such as desmosomes, which anchor cells together to distribute mechanical stress.3
• Tight junctions: Which create leakproof seals between cells to separate internal and external fluids.4

A tissue is defined as a group of structurally and functionally similar cells and their intercellular material. In animals, these are broadly classified into four types: epithelial, muscle, nerve, and connective tissues.56

From Tissues to Organs

An organ is a higher level of organization consisting of a group of different tissues that function together as a distinct structural unit. For example, the heart is composed of all four basic tissue types working in concert to pump blood. These organs are further integrated into organ systems, which perform complex physiological functions necessary for the organism's survival.6