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What Are Fibroblasts? - Definition & Explanation

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  • 0:00 What Is a Fibroblast?
  • 0:39 Proteins and Ground Substance
  • 3:15 Adaptability
  • 4:30 Lesson Summary
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Lesson Transcript
Instructor: Stephen Christensen
In this lesson, you will learn about fibroblasts. You will discover what substances they produce and why they are so important to every organ system in your body.

What Is a Fibroblast?

A fibroblast is a cell that manufactures and maintains connective tissue, the structural framework that supports the organs of all animals. Fibroblasts secrete fibrous proteins and ground substance, which together form the extracellular matrix that is the basis of connective tissue. Ground substance is composed of varying amounts of water and specialized molecules that help determine how firm or soft the extracellular matrix will be. Thus, fibroblasts give connective tissue its strength, form, and the ability to adhere to other tissue types.

Proteins and Ground Substance

Beneath a microscope, fibroblasts are fairly nondescript. Fibroblasts that are actively producing connective tissue are a bit larger than inactive, or 'resting,' fibroblasts, but even active fibroblasts are visually uninteresting. However, few cells have functions that are as fascinating as fibroblasts, nor are many cells as adaptable to different situations.

Depending on where they are and what type of connective tissue they're building, fibroblasts can secrete several different types of fibrous proteins:

Collagen is a tough, strong fiber that provides tensile and compressive strength to your organs and tissues. Collagen is the most abundant protein in the human body. If you removed the cells from one of your organs, a collagen 'skeleton' of that organ would be left behind. Collagen is the major constituent of your tendons and ligaments, and much like the tough backing on a carpet, it provides support for your skin. When you have an injury to your skin, collagen is the stuff that forms the scar. Due to the many tasks required of connective tissue, your fibroblasts 'know' how to make at least a dozen different types of collagen.

Elastin is a stretchy and resilient protein. Like a rubber band, elastin helps tissues return to their previous shape after they've been stretched. In sun-damaged skin, elastin fibers become weak and disorganized, allowing the skin to droop and sag.

Reticular fibers are a delicate form of collagen that gently cradles cells in organs where blood or other fluids must be able to percolate freely. Your liver, spleen, and lymph nodes are loaded with reticular fibers.

Fibronectin is secreted from fibroblasts in a water-soluble form but is quickly assembled into an insoluble meshwork that serves several functions: other cells use the fibronectin matrix to migrate through a tissue; fibronectin helps 'glue' connective tissues to surrounding tissue types; and fibronectin is necessary for cellular growth and specialization in many tissues.

Fibroblasts don't secrete finished collagen, elastin, fibronectin, or reticular fibers. Rather, they produce smaller, folded molecules that are modified to form the extracellular matrix after they're released. The ground substance secreted by a fibroblast has a lot to do with the type of connective tissue it produces, too. Bone, cartilage, fat, and blood are all special forms of connective tissue. What makes them radically different is the composition of their ground substance.

Adaptability

Scientists have learned that fibroblasts in muscle, lung, heart, tendons, and even around the bases of your teeth make collagen that is specifically needed in those areas of your body. If you remove these fibroblasts from your tissues and grow them in a test tube, the next few generations of fibroblasts continue to make the same type of connective tissue they made when they were in your body. This suggests that fibroblasts have a sort of genetically programmed 'memory.'

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