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Collagen Fibers Hold Us Together: Function, Structure and Types

Hannah Robinson, Wendy McDougal
  • Author
    Hannah Robinson

    Hannah is an award-winning STEM teacher and curriculum developer. She is a fully credentialed teacher of AP Biology, AP Computer Science, Chemistry, Earth Science, and Engineering, with 20 years’ experience. She has a Master’s Degree in Curriculum and Instruction from Grand Canyon University and has a Biochemistry and Physiology Degree. She has lead hikes for the National Parks Service, and is the author of two books on Ecotravel.

  • Instructor
    Wendy McDougal

    Wendy has taught high school Biology and has a master's degree in education.

Understand what collagen fibers are by learning the definition of collagen. Know where collagen fibers are found, and the various types of collagen fibers and common diseases. Updated: 11/15/2021

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Collagen Fibers

Leo is a service dog trained to detect a health crisis in a person with a collagen disorder. He is about to meet the girl he will assist, and we will see who this is in a minute. First, we will explore collagen's function in our body so we can understand the situation.

Leo the collagen disorder service dog

Picture of dog in a field with a harness on the dog

Pull at your ear lobes, puff out your cheeks, or hang onto the bars of a climbing frame, and you are feeling what collagen fibers do. Collagen is the most common protein in the human body and other mammals, and forms something called connective tissue. Collagen fibers are made of bundles of protein strands that lie on a bed of extra-cellular material outside the cells called a matrix, like spaghetti strands in a lot of thick sauce. Collagen is the most important structural fiber that holds us together. Some collagen fibers are strong and connect muscles to bones as tendons and bind joints as ligaments, while others are stretchy and wrap around things like muscles and the lens of our eye. The soft part of our ear is made of cartilage which contains collagen fibers, our long bones are made of minerals that grow from growth plates which are made of collagen tissue, and skin is held together by a stretchy lower layer called the dermis, which is criss-crossed by collagen fibers that start to sag with age.

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  • 0:30 Definition of Collagen
  • 1:47 Collagen in Connective Tissue
  • 3:20 Types of Collagen
  • 4:02 Skin Damage, Aging & Collagen
  • 5:03 Collagen-Related Diseases
  • 5:53 Lesson Summary
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Lip collagen supplement

Makeup jar labelled lip collagen

Collagen Function

The function of collagen fibers is to provide mechanical strength to keep the body together, including when we move. Although bones provide protection and leverage, collagen provides structural support between the bones, holds the organs in place without friction, and connects every single part of the body so it doesn't fall apart.

Collagen Anatomy

Collagen fibers are like super-coiled ropes of triple-ply wool. At the tiniest level, three protein strands are wound around each other into what is called a triple helix. This winding occurs inside the cell's Golgi body after the protein is made.

Triple helix of collagen protein strands

Triple helix in three colors

When this short triple helix leaves the cell, it is made into longer fibers. The triple helices are stacked, overlapped, and connected together into bundles called microfibrils (micro means small). You can see the bands of overlapped stacks in an electron micrograph.

Type I Collagen cibers from tunneling electron microscope TEM

Black and white image with banded stripes

The microfibrils are made even stronger by lining up and cross-linking the bundles into a long, parallel fiber called a macrofibril (macro means large). The macrofibril is what we call the collagen fiber. We can see the macrofibrils clearly under an optical microscope when we look at the beautiful parallel strands and matrix of a tendon.

Beautiful strong Type I tendons showing collagen macrofibrils, 400x

Red threads in wavy parallel loose arrangement

Types of Collagen Fibers

There are four main types of collagen fibers, and other types as well. You hang onto climbing bars using Type I collagen fibers in tendons and ligaments, the strongest and most fibrous type. When you pull at your ear lobe you can feel the looseness of Type II collagen fibers and matrix. Type III wraps around the muscles you use on the climbing bars so they slide over each other freely. When you puff out your cheeks, you can feel the elastic network of Type IV collagen holding your cheeks together.

Type I

Type I is the most common type of collagen fiber. The fiber bundles of Type I are organized into dense parallel threads that produce biomaterial that is stronger than steel. Tendons connecting muscle to bones (shown in the image above), ligaments binding bones to bones at joints, the ligament that keeps each tooth from falling out, the fibrous cartilage shock-absorbing disks between our vertebra (shown below/at side), and the collagen in bone are all Type I.

The wavy lines of Type I collagen fibers with dark cell blobs in the fibrocartilage between vertebrae, 100x

Wavy lines of fibers dotted with small darker dots of cells

Type II

Type II collagen is much looser packed and found in two sub-types of cartilage. Hyaline cartilage has a tough matrix found in the rings around our windpipe, the smooth surfaces on our knee joints, and the shape of our middle nose. The second sub-type is elastic cartilage that is found in our ear lobes and lower end of our nose.

Hyaline (nose) cartilage has some Type II collagen in a flexible matrix, 100x

Pink matrix interspersed with circular pattern

Type III

Type III collagen is often associated with Type I collagen, and is a very different stretchy collagen fiber called a reticular fiber. Reticule means a net in Latin. So reticular fibers have short branches going up, down, and sideways, like a net. Type III stretchy fibers are wrapped around the outside of muscle fibers and organs in an elastic sleeve to reduce friction and keep them separated from other parts. These fibers also hold our artery walls together flexibly, absorbing the pulse of pressure created by our heart beat.

Black-stained Type III collagen fibers hold cells together with stretchy four-way fibers, 400x

Black short thick threads around red cells

Type IV

Type IV is a non-fibrous structure made of short triple helix sections joined into a net, unlike the coiling of micro or macrofibrils in Types I-III. The structure is similar to a strong elastic version of tennis court netting or a fishing net. You can find Type IV underneath the skin in what is called the dermis, which is the layer below the waterproof keratin layer we see as skin. Type IV is made by epithelia, which are cells that form the body's covering and lining layers. These layers include the lining of lungs, the lining of our cheeks, and even the filtration system of the kidneys.

3-D Bioprinted skin with lower red layer (dermis) of collagen Type I and IV under the blue-green cells of the keratin top layer (epidermis), 50x

Red layer under spongy blue and green layer

Aging and Collagen Related Diseases

Sailors in ancient times noticed they had bad gums and their teeth fell out. This was because Vitamin C from fresh fruit is necessary for the body to make collagen. Due to Vitamin C deficiency, the lining of their mouth and the ligaments of their teeth degraded as the collagen aged and was not replaced. Although we are unlikely to have Vitamin C deficiency today, collagen breaks down over time in noticable ways.

Aging and Other Collagen Changes

Over time, beautifully arranged linear collagen fibers start to break down. The body may repair the fibers but produces a more muddled arrangement that has less elasticity and strength. So the the skin of an older person tends to sag and wrinkle compared with the elasticity of a baby. Smoking has been found to reduce the production and repair of Type I and III collagen under the skin by about one fifth. So smokers tend to have wrinklier, less elastic skin as they get older. The sun also speeds up the breakdown of collagen under the skin, which gets replaced by non-collagen fibers, increasing wrinkles and skin damage. New studies have found that dietary supplements of soluble collagen can assist the skin repair process as people age.

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Frequently Asked Questions

What is the function of collagen fibers?

Collagen fibers provide the strength, structural support, and connecting threads needed by the body to stay together. Different collagen fiber types have different functions, and these include linear strength of tendons, flexible strength of ear lobes, stretchy sleeves around blood vessels, and filtration nets for kidneys and under the skin.

What are the four types of collagen fibers?

Type I collagen fiber is the most common type, and is found in skin, tendons, and ligaments.

Type II collagen fiber is more elastic and softer, found in nose and ears.

Type III collagen is found with Type I collagen, and is more elastic. This is found around blood vessels, muscles, and organs holding them together.

Type IV collagen is a net that helps the body filter, such as in the kidneys, and keep layers together such as under the skin

What are collagen fibers composed of?

Collagen fibers are made of triple helices of protein fibers. These are made strong by building up the helices into bundles called microfibrils, and then grouping these bundles into macrofibrils, which are the strong collagen fibers that we can see under the optical microscope.

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