What is Connective Tissue?

Rheumatology deals in conditions that affect the connective tissue of the body, so its important to understand what connective tissue is.

Connective tissue is the most diverse and large amount of tissue in the body. It is incredibly important for the body  – says the Rheumatologist you say!! – but seriously, jokes aside, it is enormously important to the functioning and health of the body.

Connective tissue is a diverse array of tissue that as the name says, connects, as well as binds, ensheathes, supports and is part of the communication and transportation in the body. Nearly every organ in the body has connective tissue as a vital part of it. It is in and around parts of the body, connecting different tissues throughout the body.

Connective tissue is made up of many different components, and in the same way that there are many different organs, so too there are different forms of connective tissue that have different functions according to their different structure and make up.

Different types of connective tissue:

There are different types of connective tissue categorised according to their microscopic structure. Different structure and composition is needed for different functions and roles in the body.

  • Connective tissue ‘proper’
    • Loose, including fat
    • Dense, including tendons and ligaments
  • Fluid Connective Tissue:
    • Blood
    • Lymph
  • Supportive Connective Tissue
    • Bone
    • Cartilage,

Lymphoid tissue
Bone marrow
Fibrous tissue, including tendons and ligaments

Are all forms of connective tissue.

Its interesting to note that there are so many different types of connective tissue and it would be easy to consider that they are completely different. At their core, all of these tissues originate from the same place in the developing embryo, a middle layer of 3 layers called the ‘mesoderm’ and they simply differentiate from there according to the function.

With particular reference to Rheumatology, joints are part of the connective tissue system, as they are made of bone, lined by cartilage on the surfaces that meet, with tendons moving them and fibrous material binding them on the outside. Muscles on the other hand are not connective tissue, they are a different type of tissue originating from a different place in the developing embryo.

What are the functions of connective tissue?

There is still much to learn about the role of connective tissue and there is ongoing research exploring the role of the extracellular matrix in cellular health, but what we do know is that:

  • It connects different tissues in the body
  • Provides a structural framework for the body
  • It holds organs in their place and it cushions, supports and protects them
  • It is thought to be where inflammation and the defence/protection of the body occurs, as the cells for inflammation live in connective tissue
  • It stores energy,
  • It is involved in transportation and intercellular communication

What makes up connective tissue?

  • Cells and extracellular matrix.

The defining property of connective tissue is that the the extracellular matrix (which is the part of the tissue surrounding the cells) is so large, and the actual cells are relatively far apart whereas in organs of specialised function such as the liver, or the thyroid, the cells are close together, like building blocks. The main component of the Extracellular matrix is water.

The main cells in connective tissue are:

Fibroblasts – these cells produce the extracellular matrix
Fat cells (aka adipocytes)
Mast cells, lymphocytes, or macrophages. These are key cells in inflammation.