Connective tissue is a concept of medical histology which is a science that deals with research and education of the body tissues in addition to its structure and function. This concept is usually taught to second year medical students within the framework of a course about histology. In this article, I will give an overview of the types of connective tissues and its structure and function in the human body.
Connective tissue is a type of tissue in the body which has several functions such as giving support to other tissues in the body such as occurs with bone tissue which supports the muscles of the body and gives it attachment points. Also connective tissue has a function that is related to the immune system such as that which occurs with white blood cells, part of the blood that is considered as a liquid connective tissue. This is in addition to the lymph in the body which is also a liquid connective tissue.
Bone which is a type of connective tissue has in addition to its being a framework to support the body especially the muscles is the site of the production of red blood cells and white blood cells. The basic structure of all connective tissues in the body includes a cellular component and an extracellular matrix. The matrix of the connective tissue is located between its cells. The extracellular matrix in turn is composed of two components. These are: protein fibers and ground substance.
The ground substance is the material between the cells and the protein fibers. The extracellular matrix is usually formed by specialized cells in the specific connective tissue. For example, the type of cells which is called fibroblasts is present in several types of connective tissues and is specialized in secreting the fibers and the ground substance in certain types of connective tissues. Also in the bone tissue a type of cells which is called osteoblasts is responsible for secreting the extracellular matrix in this connective tissue. This is in addition to its other function that is related to the deposition of calcium salts on the bone tissue.
In addition, in cartilage which is another form of connective tissue a special type of cells which are called chondroblasts is specialized in the secretion of extracellular matrix of the cartilage connective tissue. These blast cells have the ability to differentiate into mature type of cells that is characteristic of that connective tissue. Once the blast cells are differentiated they cannot differentiate anymore but they retain their ability to secrete the extracellular matrix material.
Connective tissue differs than epithelial tissue by their rich vascular supply which is absent in the case of epithelial tissues. Cartilage is an exception since it does not have a blood supply. Connective tissue however has nerve supply similar to that in epithelial tissues. Cells of connective tissue include the blasts cells which have already been discussed. In addition, macrophages are also part of the connective tissues especially in the lungs and the spleen. They are derived from precursor cells which are called monocytes.
The blood is considered as a type of connective tissue in which the extracellular matrix in this case is the blood plasma. Plasma cells are also part of a connective tissue. They are derived from immune cells which are called B lymphocytes. most plasma cells reside in connective tissues although they can circulate also in the blood. Adipose cells or adipocytes are a type of connective tissue cells which specialize in storing lipids in the form of triglycerides. These cells are found underneath the skin and around other organs in the body such as the heart and the kidney.