What is Synovial Fluid?

Brigette Banaszak, Adrianne Baron
  • Author
    Brigette Banaszak

    Brigette has a BS in Elementary Education and an MS in Gifted and Talented Education, both from the University of Wisconsin. She has taught math in both elementary and middle school, and is certified to teach grades K-8.

  • Instructor
    Adrianne Baron

    Adrianne has a master's degree in cancer biology and has taught high school and college biology.

Learn what is synovial fluid and synovial fluid function. Understand the location and composition of synovial fluid, as well as how it is produced and analyzed. Updated: 01/09/2022

What Is Synovial Fluid?

Synovial fluid is a thick fluid found in all the movable joints of the human body. A synovial fluid definition should also include the function of the fluid, which is to lubricate the joint and provide a cushion for the ends of the bones. The end of the bones in a moving joint are covered in cartilage and synovial fluid reduces the friction caused when these bones move against one another in the joint. The fluid itself is thick, pale yellow, and made up of blood plasma and hyaluronic acid. Plasma is the liquid part of blood and contains proteins, while hyaluronic acid makes the plasma viscous, which means thicker, so it can better cushion and lubricate the joint.

Synovial Fluid Location

Where is synovial fluid found? The joints in the body that are movable and contain synovial fluid are called synovial joints. The ends of the bones in these joints are covered with a thin layer of articular cartilage, designed to protect the bones from wear and tear. Lining the inside of the joint cavity is a thin synovial membrane (or synovium), which is what produces synovial fluid and encloses the entire joint.


Synovial fluid cushions and protects the cartilage-covered ends of the bones in a moving joint

Synovial fluid cushions and protects the cartilage-covered ends of the bones in a moving joint


Synovial Fluid Functions

What does synovial fluid do? Synovial fluid has several functions inside the joint:

  • Synovial fluid lubricates the joint and allows the ends of the bones to move without friction.
  • Synovial fluid contains nutrients needed for the cartilage at the ends of the bones and carries away waste from within the joint capsule.
  • Synovial fluid acts as a shock absorber within the joint.

The main function of synovial fluid is to allow the ends of the bones in a joint to move freely without rubbing against one another. In a movable joint, the ends of bones are covered with a layer of cartilage that helps to protect the bones and allows them to move as the muscles, ligaments, and tendons in and around the joint work. Without the layer of articular cartilage protecting the bones, the ends of the bones would rub against one another every time the joint moved, potentially causing the bones themselves to chip or crack. The thick synovial fluid prevents the articular cartilage on the end of one bone from touching the cartilage on the end of the next bone. This thin layer of fluid reduces friction in the joint and allows it to move freely and without resistance.

Synovial fluid carries nutrients needed to keep the cartilage covering the ends of the bones healthy. The nutrients are circulated within the joint by the thick fluid, which also carries away waste products produced as cells regenerate.

A final function of synovial fluid is to act like a shock absorber within the joint. The thick fluid helps to absorb shocks within the joint and protect the articular cartilage from damage.

Synovial Fluid Explained

I want you to think for a minute about something that you have probably encountered at some point in your life. Have you ever noticed the hinges on a door in your house squeaking? Or maybe you've heard a rubbing noise as you are driving your car? When these things happened, you likely decided to look at the door hinge or the car engine and then quickly realized that the moving parts in the hinge or engine were dry and rubbing against each other every time the door opened or the engine was running. Then, you probably used some type of lubricant in order to moisten the door hinge or add engine oil in order to moisten the engine parts.

By doing this, you made the parts smooth and moist so they could glide past each other without rubbing together and making the squeaking noise. The other thing that happened when you did this is that you decreased the amount of damage that would occur to the door hinge or engine, which helps to make them lasts longer. This is what synovial fluid does for us.

Synovial fluid is the clear, pale yellow fluid that is contained in every joint in our bodies. It is derived from plasma, which is the protein-salt solution that makes up the liquid portion of our blood. Synovial fluid contains large amounts of hyaluronic acid, which helps to make the fluid more viscous, or thicker.

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Synovial Fluid Analysis

What is a synovial fluid analysis and why would it be needed? Synovial fluid analysis occurs when a sample of synovial fluid is removed from the joint capsule and analyzed. This procedure might be ordered if the joint is red, warm, swollen, or painful. The fluid analysis can diagnose issues such as a bleeding disorder, a bacterial infection, or one of several types of arthritis.

Synovial Fluid Function

The synovial fluid in our joints is there to allow the bones that make up the joint to be able to slide past each other without causing damage to the ends of the bones. There is a thin layer of cartilage, called the articular cartilage, that is there to protect the ends of the bones. The cartilage must be maintained in order for the bones to not fracture or crack every time we move.

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Video Transcript

Synovial Fluid Explained

I want you to think for a minute about something that you have probably encountered at some point in your life. Have you ever noticed the hinges on a door in your house squeaking? Or maybe you've heard a rubbing noise as you are driving your car? When these things happened, you likely decided to look at the door hinge or the car engine and then quickly realized that the moving parts in the hinge or engine were dry and rubbing against each other every time the door opened or the engine was running. Then, you probably used some type of lubricant in order to moisten the door hinge or add engine oil in order to moisten the engine parts.

By doing this, you made the parts smooth and moist so they could glide past each other without rubbing together and making the squeaking noise. The other thing that happened when you did this is that you decreased the amount of damage that would occur to the door hinge or engine, which helps to make them lasts longer. This is what synovial fluid does for us.

Synovial fluid is the clear, pale yellow fluid that is contained in every joint in our bodies. It is derived from plasma, which is the protein-salt solution that makes up the liquid portion of our blood. Synovial fluid contains large amounts of hyaluronic acid, which helps to make the fluid more viscous, or thicker.

Synovial Fluid Function

The synovial fluid in our joints is there to allow the bones that make up the joint to be able to slide past each other without causing damage to the ends of the bones. There is a thin layer of cartilage, called the articular cartilage, that is there to protect the ends of the bones. The cartilage must be maintained in order for the bones to not fracture or crack every time we move.

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Frequently Asked Questions

What is synovial fluid and why is it important?

Synovial fluid is a thick fluid found in all the movable joints of the human body. Its purpose is to lubricate the joint and provide a cushion for the ends of the bones. Synovial fluid reduces the friction caused when these bones move against one another within the joint capsule.

What are the 3 functions of synovial fluid?

Synovial fluid has three functions inside the joint:

  • It allows the ends of the bones to move without friction and lubricates the joint.
  • It contains nutrients needed for the cartilage at the ends of the bones and carries away waste.
  • It acts as a shock absorber.

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