Connective tissue is one of the four major tissue types and it is found in every organ system throughout the entire human body. Because its composition varies significantly according to its function and location, connective tissue includes many subtypes of tissues that make up arteries, joints, tendons, blood and even bones.
However, despite their diversity, all types of connective tissue consist of a combination between widely spaced out cells (fibroblasts, macrophages, lymphocytes etc.) that produce the extracellular matrix, which contains protein fibers (reticular, collagen and elastic fibers), ground substance and tissue fluid.
Based on composition, connective tissue is classified into two major types: loose connective tissue (further grouped into areolar, adipose and reticular tissue) and dense connective tissue (which is grouped into regular and irregular connective tissue).
The role of connective tissue is complex and involves multiple functions such as:
1. Ensuring support and protection for tissues and organs.
The most important function of connective tissue is to support all the other tissues in the body and give the body its characteristic shape. Bones form the skeleton, which supports the muscles and ensures locomotion; muscles are bound and nourished through areolar tissue and finally, cartilages provide added strength and cushion joints. Adipose tissue also has a protective role because it pads vulnerable areas of the body and keeps them warm.
2. Providing defense through the immune function.
Connective tissue contains macrophages, a type of white blood cell that protects the body from being invaded by harmful organisms and produces substances that stimulate the entire immune system.
3. Transporting nutrients and waste products.
Blood and blood vessels are the foundation of the circulatory system; together, they ensure the transport of nutrients and the elimination of waste products that result from the metabolic function of the body.
4. Energy storage and thermoregulation.
Adipose tissue is where the body can store energy as lipids through adipocytes, thus creating a valuable energy reserve. Adipose tissue also shelters the body from low temperatures and thus, helps maintain homeostasis. Specialized adipocytes form brown fat, which can actually produce heat by burning fat (this influences a person’s metabolic rate).
5. Tissue regeneration following injury or trauma.
Fibroblasts are important cells that help regenerate tissue after injury by creating new structural fibers and ground substance. Their action can sometimes result in visible scars (which are in fact an accumulation of collagen fibers).
Because of its varying composition and function, connective tissue is a complex component of the human body and one of the building blocks that helps create and sustain it.