Understanding Connective Tissue

Cartilage, rather than bone, forms the fetal skeleton and is softer and more flexible than bone. Unlike cartilage, bone has both vascular and nervous networks running through it.

Connective tissue has three main components: fibers, ground substance, and cells (fibroblasts, adipocytes, macrophages, mast cells, and leukocytes). Typically, connective tissue contains a relatively low proportion of cells, and a very high proportion of ground substance and fibrous proteins, such as collagen. Blood and lymph is sometimes considered a component of connective tissue as well.

Connective tissue binds, supports, and fills spaces in the body. It consists of cells surrounded by an extracellular matrix. The make-up of this matrix is essential to defining the properties of the given connective tissue type. The extracellular matrix of blood is aqueous and filled with platelets and protein factors, while the matrix of bone is composed of hydroxyapatite crystal.

Osteoblasts contribute to the ossification process by working to build bone. They cannot do so as individual cells, but rather need to be arranged into osteons in the bone to function. Osteoblasts are regulated by a number of factors depending on the body's need for bone creation or resorption, including being inhibited by PTH.

Cells are also a critical component of connective tissue and are typically suspended in the ground substance. Cells that are a part of connective tissue include fibroblasts (cells that produce fibers), mast cells (involved in histamine-mediated inflammatory response), and adipocytes (fat cells). Staining methods can show these cell types within the connective tissue. Other connective tissue cells include osteocytes (bone cells), and chondrocytes (cartilage cells).

Blood, bone, tendons, ligaments, and cartilage are all types of connective tissue. Bone and cartilage provide the framework for the body, as well as protect the internal organs of the body. Blood is responsible for transportation of oxygen and other nutrients throughout the body. Tendons transfer the force created by muscle tissue to the bones, allowing for movement.

Connective tissue is not responsible for communicating pain to the brain, as the sensation of pain is created by signals from the nervous system. The four types of tissue are connective, epithelial, muscular, and neural.

The connective tissue is found throughout the body in between other tissues and cell types. Connective tissue functions to both connect and separate the different tissue types.

Cartilage also performs a structural function, but it is more flexible than bone. Furthermore, it doesn't have nerves or blood vessels. This explains why a broken bone heals quite well (sometimes the broken bone becomes stronger than it was before) while cartilage does not heal/regenerate nearly as fast. They both secrete matrices, and are made up of collagen and calcium salts.

Collagenous fibers connect tissue types and bind elements of the musculoskeletal system to one another. Types of collagenous fibers in connective tissue include blood vessels, ligaments, and tendons. Stratified epithelium is comprised of layers of epithelial cells, which function as a covering/lining to a body structure that is subject to lots of friction.

In the human body, not all types of connective tissue contain fibers. Examples of non-fibrous connective tissues are blood, adipose tissue, and bone which are made of plasma and cells, fat, and mineralized extracellular matrix, respectively.