Connective Tissue and Collagen Basics

These are notes taken from the site:

Connective Tissue

The human body is composed of just four basic kinds of tissue: nervous, muscular, epithelial, and connective tissue

Connective tissue is the most abundant, widely distributed, and varied type. It includes fibrous tissues, fat, cartilage, bone, bone marrow, and blood. As the name implies, connective tissues often bind other organs together, hold organs in place, cushion them, and fill space.


Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals.

It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content.

Types and associated disorders

Collagen occurs in many places throughout the body. Over 90% of the collagen in the body is of type one.

So far, 28 types of collagen have been identified and described. The five most common types are:

  1. Collagen I: skin, tendon, vascular ligature, organs, bone (main component of the organic part of bone)
  2. Collagen II: cartilage (main component of cartilage)
  3. Collagen III: reticulate (main component of reticular fibers), commonly found alongside type I.
  4. Collagen IV: forms bases of cell basement membrane
  5. Collagen V: cells surfaces, hair and placenta

Collagen-related diseases most commonly arise from genetic defects or nutritional deficiencies that affect the biosynthesis, assembly, postranslational modification, secretion, or other processes involved in normal collagen production.


Collagen is one of the long, fibrous structural proteins whose functions are quite different from those of globular proteins such as enzymes. Tough bundles of collagen called collagen fibers are a major component of the extracellular matrix that supports most tissues and gives cells structure from the outside, but collagen is also found inside certain cells

Collagen has great tensile strength, and is the main component of fascia, cartilage, ligaments, tendons, bone and skin. Along with soft keratin, it is responsible for skin strength and elasticity, and its degradation leads to wrinkles that accompany aging. It strengthens blood vessels and plays a role in tissue development. It is present in the cornea and lens of the eye in crystalline form.

Additional Function

Collagens interact with other extracellular matrix proteins and play important roles in regulating the activities of the cells with which they interact. Cells associate with collagen via cell surface receptors, and through such interactions collagens may have a profound impact on cell proliferation, migration, and differentiation.

Here are links to several informative posts:

You can find all posts about collagen using the tag:

Below is  a more technical description of connective tissue:

The extracellular matrix

The extracellular matrix is a meshwork of proteins and carbohydrates that binds cells together or divides one tissue from another.

The extracellular matrix is the product principally of connective tissue , one of the four fundamental tissue types

In the connective tissue, matrix is secreted by connective tissue cells into the space surrounding them, where it serves to bind cells together.

The extracellular matrix forms the basal lamina, a complex sheet of extracellular matrix molecules that separates different tissue types, such as binding the epithelial tissue of the outer layer of skin to the underlying dermis, which is connective tissue.

Connective tissue is distinguished from the other types in that the extracellular material (matrix) usually occupies more space than the cells do, and the cells are relatively far apart

The matrix of connective tissue typically consists of fibers and a featureless ground substance. The most abundant fiber in connective tissues is a tough protein called collagen. Tendons, ligaments, and the white stringy tissue (fascia) seen in some cuts of meat are composed almost entirely of collagen, as is leather, which consists of the connective tissue layer (dermis) of animal skins. Collagen also strengthens bone and cartilage

The ground substance may be liquid, as in blood; gelatinous, as in areolar tissue; rubbery, as in cartilage; or calcified and stony, as in bone. It consists mainly of water and small dissolved ions and organic molecules, but the gelatinous to rubbery consistency of some tissues results from enormous protein-carbohydrate complexes in the ground substance.


Collagens are the principal proteins of the extracellular matrix. They are structural proteins that provide tissues with strength and flexibility, and serve other essential roles as well. They are the most abundant proteins found in many vertebrates. There are at least nineteen collagen family members whose subunits, termed α chains, are encoded by at least twenty-five genes

Some collagens, most notably collagen types I, II, III, and V, assemble into large, ropelike macrofibrils once they are secreted into the extracellular matrix.

Type IV collagen, which is found in the basal lamina, does not assemble into a fibril since its subunits retain their propeptides following secretion from a cell. Its triple helix has a series of interruptions in the GLY–X–Y repeating motif, preventing the subunits from binding quite as tightly, and giving the molecule more flexibility. Type IV collagen forms a scaffold around which other basal lamina molecules assemble

The fibrillar collagens are also associated with a class of collagen molecules that themselves do not form fibrils but that appear to play an important role in organizing the highly ordered arrays of collagen fibrils that occur in some connective tissues. Examples of this collagen class include type IX and type XII collagen.


Another good general biology resource in outline format:

These pages represent an online biology textbook.

It has always seemed to me that the many parts that make up the subject of biology are related to each other more like the nodes of a web than as a linear collection of independent topics. So I believe that the power of hypertext will be better suited to learning about biology than is the linear structure of a printed textbook.

One thought on “Connective Tissue and Collagen Basics

  1. Pingback: Collagens in Energy Metabolism and Metabolic Diseases | EDS Info (Ehlers-Danlos Syndrome)

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