CONNECTIVE TISSUES EXAMPLES BONES and CARLILAGE

connective tissue serves a connecting function. It supports and binds other tissues in the body. Unlike epithelial tissue, which has cells that are closely packed together, connective tissue typically has cells scattered throughout an extracellular matrix of fibrous proteins and glycoproteins attached to a basement membrane. The primary elements of connective tissue include a ground substance, fibers, and cells.

The ground substance acts as a fluid matrix that suspends the cells and fibers within the particular connective tissue type. Connective tissue fibers and matrix are synthesized by specialized cells called fibroblasts. There are three main groups of connective tissues: loose connective tissue, dense connective tissue, and specialized connective tissue.

Loose Connective Tissue

In vertebrates, the most common type of connective tissue is loose connective tissue. It holds organs in place and attaches epithelial tissue to other underlying tissues. Loose connective tissue is named so because of the "weave" and type of its constituent fibers. These fibers form an irregular network with spaces between the fibers. The spaces are filled with ground substance. The three main types of loose connective fibers include collagenous, elastic, and reticular fibers.

• Collagenous fibers are made of collagen and consist of bundles of fibrils that are coils of collagen molecules. These fibers help to strengthen connective tissue.

• Elastic fibers are made of the protein elastin and are stretchable. They help to give connective tissue elasticity.
• Reticular fibers join connective tissues to other tissues.

Loose connective tissues provide support, flexibility, and strength required to support internal organs and structures such as blood vessels, lymph vessels, and nerves.

Dense Connective Tissue

Another type of connective tissue is dense or fibrous connective tissue, which can be found in tendons and ligaments. These structures help attach muscles to bones and link bones together at joints. Dense connective tissue is composed of large amounts of closely packed collagenous fibers. In comparison to loose connective tissue, dense tissue has a higher proportion of collagenous fibers to ground substance. It is thicker and stronger than loose connective tissue and forms a protective capsule layer around organs such as the liver and kidneys.

Dense connective tissue can be categorized into dense regular, dense irregular, and elastic connective tissues.

• Dense regular: Tendons and ligaments are examples of dense regular connective tissue.
• Dense irregular: Much of the dermis layer of the skin is composed of dense irregular connective tissue. The membrane capsule surrounding several organs is also dense irregular tissue.
• Elastic: These tissues enable stretching in structures such as arteries, vocal cords, the trachea, and bronchial tubes in the lungs.

Specialized Connective Tissues

Specialized connective tissues include a number of different tissues with specialized cells and unique ground substances.

Some of these tissues are solid and strong, while others are fluid and flexible.

Adipose

Adipose tissue is a form of loose connective tissue that stores fat. Adipose lines organs and body cavities to protect organs and insulate the body against heat loss. Adipose tissue also produces endocrine hormones.

Cartilage

Cartilage is a form of fibrous connective tissue that is composed of closely packed collagenous fibers in a rubbery gelatinous substance called chondrin. The skeletons of sharks and human embryos are composed of cartilage. Cartilage also provides flexible support for certain structures in adult humans including the nose, trachea, and ears.

Bone

Bone is a type of mineralized connective tissue that contains collagen and calcium phosphate, a mineral crystal. Calcium phosphate gives bone its firmness.

Blood

Interestingly enough, blood is considered to be a type of connective tissue. Even though it has a different function in comparison to other connective tissues, it does have an extracellular matrix. The matrix consists of the plasma with red blood cells, white blood cells, and platelets suspended in the plasma.

Lymph

Lymph is another type of fluid connective tissue. This clear fluid originates from blood plasma that exits blood vessels at capillary beds. A component of the lymphatic system, lymph contains immune system cells that protect the body against pathogens.

Animal Tissue Types

In addition to connective tissue, other tissue types of the body include:

• Epithelial Tissue: This tissue type covers body surfaces and lines body cavities providing protection and allowing for the absorption and secretion of substances.
• Muscle Tissue: Excitable cells capable of contraction allow muscle tissue to generate body movement.
• Nervous Tissue: This primary tissue of the nervous system allows for communication between various organs and tissues. It is composed of neuronsand glial cells.