Connective tissue

Connective tissue is a special kind of biological tissue found between other tissues in the body. It is one of the four main types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue.

Connective tissue is made up of three main parts: elastic and collagen fibers, ground substance, and cells. It helps hold the body together and supports other tissues.

It comes from the mesenchyme, which comes from the mesoderm, one of the three embryonic germ layers in developing animals. Examples of connective tissue include the three meninges, which protect the brain and spinal cord, as well as blood and lymph, which carry important substances throughout the body.

The word "connective tissue" was first used in 1830 by Johannes Peter Müller. Connective tissue includes many kinds of cells, such as fibroblasts, adipocytes, macrophages, mast cells, and leukocytes, which help keep the body healthy.

Types

Connective tissue can be divided into two main types: connective tissue proper and special connective tissue.

Connective tissue proper includes loose connective tissue, which has space between its fibers, and dense connective tissue, which has tightly packed fibers. Dense connective tissue can be dense regular, found in tendons and ligaments, or dense irregular, which gives strength in many directions.

Special connective tissue includes supportive tissues like bone and cartilage, and fluid tissues such as blood and lymph. These are a type of fascia, with blood and lymph called liquid fascia. Other special connective tissues include fibrous, elastic, and lymphoid tissues. When wounds heal, new connective tissue called granulation tissue forms.

Membranes can be made of connective tissue or epithelial tissue. Connective tissue membranes include the meninges, which cover the brain and spinal cord, and synovial membranes, which line joint cavities.

Fibrous types

The body has special fibers that help hold everything together. These include collagen fibers, elastic fibers, and reticular fibers. Between our cells, there is a clear, sticky fluid called ground substance. This fluid helps keep the collagen fibers in place.

Some connective tissues, like adipose tissue (which is fat) and blood, don’t have a lot of collagen, but they still need it to stay in shape. One type of collagen, called Type I collagen, is very common and makes up a big part of the proteins in our bodies.

Function

See also: Epithelial-mesenchymal transition

Connective tissue has many important jobs in the body. It depends on the cells and fibers it contains.

Some types of connective tissue, like loose and dense irregular connective tissue, help move oxygen and nutrients from blood vessels to cells. They also take away carbon dioxide and waste. These tissues help organs stay strong and not tear easily.

Other types, like dense regular connective tissue, are important parts of tendons, ligaments, and other body structures.

There are special kinds of connective tissue found in embryos and in the umbilical cord that help with growth and development. The body also has many different types of cells and tissues, like fat, blood, cartilage, and bone. All of these belong to the connective tissue family. Immune cells are found in connective tissue, helping to protect the body.

Clinical significance

Many health problems are related to connective tissue. Some of these include special growths, conditions you are born with like Marfan syndrome, weakening of tissue, diseases that affect the body’s defense system, and diseases of the blood vessels. One example is scurvy, which happens when there isn’t enough vitamin C to help make collagen, a key part of connective tissue.