The medical or veterinary term "fibrous capsule" refers to either an external layer which surrounds the articular capsule on a synovial join, or to the resilient, external membrane that envelopes certain organs, such as the liver and kidneys. In all cases, the purpose of the fibrous capsule is to provide support and protection to the organ or joint it encases.
Background Information on Joints
Synovial joints allow a person or animal to bend his limbs and flex his back. The connections between vertebrae and the junction of pelvis and vertebrae are also included as synovial joints. Synovial joints are made up of two bone ends, which are covered by a resilient and smooth articular cartilage. This cartilage allows for frictionless joint movement. The stability of each joint is maintained by a fibrous capsule. This capsule attaches to bones and the collateral ligaments, which attach to the sides of the joint and gives stability to the entire structure.
The fibrous capsule, together with the synovial membrane is part of the joint capsule. This capsule is essential to the optimal functioning of synovial joints. The capsule limits unnecessary movement, while providing stability to the joint. Fibrous capsules are composed of thick fibrous connective tissue, which forms a protective sleeve around the joint. The capsule is attached to the bones forming the synovial joint at specific zones. The fibrous capsule is found in different thicknesses, depending on the amount of stress to which it is exposed. These capsules may incorporate tendons on specific joints.
Background Information on External Membranes
Internal organs, including the liver and kidneys, are surrounded by, and protected from, infection and physical trauma by a fibrous capsule. Fibrous capsules encase and provide support and physical protection to all internal organs. Through this protection, humans and animals can be highly active by running and jumping without rupturing or exposing the internal organs to physical trauma.
Role in Functioning of Internal Organs
The function of the fibrous capsule, which encases the various internal organs, is the same for each individual organ or pair of organs. In the case of the kidneys for example, this strong capsule is composed of connective tissue and tightly contains each of the body's two kidneys. The fibrous capsule offers support to the internal kidney tissue. As with each internal organ, the kidney performs a unique and totally indispensable function. In the case of the kidney, this function is to remove waste products from the body and to filter the blood. The kidneys are able to function on an ongoing basis, through the protection provided by the fibrous capsule.