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Organ system histology
Cartilage is an avascular, smooth, and elastic tissue with various forms that allow it to function in a variety of ways.
The majority of the tissue consists of extracellular matrix or ECM, and only a relatively small number of chondrocyte cells.
Based on the appearance and specific function, cartilage is separated into three main types: hyaline cartilage, elastic cartilage, and fibrocartilage.
Hyaline cartilage has a “glassy” appearance and can be found on many articular surfaces as well as cartilage that provides structural support.
Elastic cartilage contains a dense network of branching elastic fibers that allow it to be more flexible, which is why it’s often found in structures that need to be firm, yet still flexible.
Let’s first focus on hyaline cartilage, which is the most common type of cartilage.
This image is an example of hyaline cartilage on the articulating surface of a long bone, with the articulating surface located at the top of the image.
The image on the right is a longitudinal section of the trachea, which is an example of hyaline cartilage providing structural support.
Both images were stained with hematoxylin and eosin or H&E for short. With this stain, the cartilage stains a dark purple due to its strong affinity for hematoxylin.
Cartilage is a unique connective tissue in that it is smooth, elastic, and lacks blood vessels. Its primary function is to provide cushioning and support for the body's joints and other structures, such as the C-shaped rings supporting the trachea. The matrix of cartilage is composed of collagen fibers and proteoglycans, which are highly charged proteins that bind to water. This combination of collagen and proteoglycans gives cartilage its characteristic spongy texture.
Note that there are three types of cartilage. There is hyaline cartilage characterized by an extracellular matrix with a "glassy" appearance. hyaline cartilage is found in the trachea and the articulating surfaces of the long bones. Second is the elastic cartilage, characterized by a dense network of elastic fibers. Elastic cartilage is commonly found in the epiglottis and the pina of the external ear.
Finally, there is fibrocartilage which is a combination of hyaline cartilage and dense connective tissue. This one is found in the knee meniscus and the intervertebral discs. Over time, cartilage can break down due to wear and tear injury or disease. When this happens, the affected joint may become painful and stiff, and in severe cases, the joint may no longer be able to move properly.
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