Connective tissue (CT) is a fibrous tissue. It is one of the four traditional classes of tissues (the others being epithelial, muscle, and nervous tissue). It is the most diverse tissue and is found throughout the body. In fact, the entire framework of the skeleton, along with the different specialized connective tissues from the crown of the head to the toes, determine the body's form, and act as an entity to carry out all body processes.
CT has three main components: cells, fibers, and extracellular matrix (Figure 2), all immersed in the body fluids. Fibroblasts are the cells responsible for the production of connective tissue. Together, the interaction of the fibers, extracellular matrix, and body water form the whole of the pliable connective tissue. Cells are distributed throughout an extracellular fluid. Ground substance is a clear, colorless, viscous fluid containing glycosaminoglycans and proteoglycans to fix the body water and the collagen fibers (Figure 3) in the intercellular spaces. Ground substance slows the spread of pathogens. Not all types of CT are fibrous; examples include adipose tissue and blood. Among other functions, adipose tissue gives "mechanical cushioning" to the body. Although there is no dense collagen network in adipose tissue, groups of adipose cells are kept together by collagen fibers and collagen sheets, keeping fat tissue under compression in place (e.g., the sole of the foot). The matrix of blood is plasma. Both the ground substance and proteins (fibers) create the matrix for CT.
Connective tissues make up a variety of physical structures, including tendons and the connective framework of fibers in muscles, capsules, ligaments around joints, cartilage, bone, adipose tissue, blood, and lymphatic tissue. CT is classified into three subtypes: Embryonic CT, Proper CT, and Special CT. The Proper CT subtype includes dense regular CT, dense irregular CT, and loose CT. The Special CT subtype includes cartilage, bone, adipose tissue, blood, hematopoietic tissue (tissue that makes blood cells), and lymphatic tissue. Functions of connective tissue include: storage of energy, protection of organs, providing structural framework for the body, and connection of body tissues.