Connective tissue is tissue that supports, binds, or separates more specialized tissues and organs of the body. Connective tissue serves as packing, holds the cells of organs together, passes on nutrients to other tissues from the blood, and may be active in fighting disease-causing organisms. The cells in connective tissue are always well spaced in a thick, fluid base substance, or matrix, in which there may also be long, thin threads called fibers.
Types of connective tissue proper
The most common type of connective tissue is areolar tissue. It forms a layer beneath the skin and the lining of the gut, and is also a packing material between muscles and other organs. It consists of a jelly-like matrix in which there are several kinds of cells and interlacing bundles of fibers. The fibers are of two kinds, white and yellow. The white fibers are very resistant to stretching but the yellow fibers can be stretched and are called yellow elastic fibers. Some of the cells are able to consume and destroy germs and so play a valuable part in the body's defensive system against disease.
Some tissues consist almost entirely of white fibers. Examples of this white fibrous tissue are tendons, which join muscle to bones, ligaments, which bind bones together at joints, and the protective covering of organs such as muscles.
Yellow elastic tissue is made up mainly of yellow elastic fibers. The ligaments that hold the bones of the backbone together are yellow elastic tissue.
Reticular tissue is a connective tissue which occurs as thin sheets. It surrounds nerve and muscle fibers and also forms the basement membrane of epithelia.
Some connective tissue cells are able to store fat. Such adipose tissue is situated mainly in the deep layers of the skin and the mesentery (the thin sheet of tissue which holds the intestine in place).
Types of specialized connective tissue
Bone and cartilage, which are skeletal tissues, are often included with connective tissues as they have many similarities but the ground substance in them is solid whereas in connective tissue it is fluid. Blood is also considered to be a specialized type of connective tissue.