Difference between Hyaline Cartilage and Elastic Cartilage

Types of Cartilage

Difference between Hyaline and Elastic Cartilage is something that greatly aids with the proper functioning of the human body, each contributing in their own unique and individual ways. Being both cartilage, Hyaline and Elastic cartilage greatly assist in the development of the fetus in the womb and is are essential to its correct and proper structuring of unformed bones.

So, What Exactly Is Cartilage?

Cartilage is a flexible type of connective tissue that is made up of cells called chondrocytes as well as from the materials that they secrete. The relatively stiff structure that cartilage boasts plays a paramount role in the development of the formation of bones during a fetus’s early stages of progress. The skeleton is first laid out in its form as cartilage, thereafter being replaced by the more solid structure of bones.

The chondrocytes rely on a process of diffusion to obtain their needed nutrients. Unlike bones, cartilage is avascular, meaning that is has no blood vessels for the transport of fresh blood to the cartilage. Due to this lack of blood supply, cartilage has a much longer healing process and time when compared to the healing time of bones. The base structure of cartilage when observed under a microscope, is vastly less organized that the structure of a bone, further complicating the healing time of cartilage. When cartilage needs to be remodeled, it is done by the effects of the changes and rearrangements of the cartilage’s collagen matrix, responding to tensile and compressive forces that is experiences.

There are 3 main types of cartilage that make up the human body:

• Hyaline Cartilage– the most common, and is found on the ribs, nose, larynx, trachea, and is the pre-cursor to a bone.
• Fibrocartilage – is the strongest cartilage, and is found in the in intervertebral discs, joint capsules and ligaments.
• Elastic Cartilage – provides strength and shape maintenance, and can be found in the external ear, epiglottis and the larynx.

Hyaline Cartilage

Of the three main cartilages found in the body, in adults, Hyaline cartilage is the most widespread. Forming the articular surfaces of long bones, between the ribs, the rings of the trachea in the throat and some parts of the skull. Hyaline cartilage has been given its name due to its glossy appearance, and is predominantly made up of collagen, although it displays few collagen fibers. In an embryo, hyaline cartilage is first formed before the bones solidify. Some of the hyaline cartilage development during the stages of the fetus remain through until adulthood. The most common site where hyaline cartilage is found in adults include:

• The upper respiratory tract: the nose, larynx, trachea and bronchi. Cartilage is used in these areas to prevent the airways from collapsing during inhalation.
• The articulating surfaces of bones: the cartilage here prevents bones from rubbing and creating friction against another bone as part of a synovial joint.
• The epiphyseal plates of bones: these are the growth plates attached to the ends of the body’s long bones. They assist during adolescent growth and are replaced by solid bone once growth is complete.
• The rib termini (costal cartilages): are segments of cartilage that connect the ribs and the sternum, helping to move the ribs in a forward motion. This cartilage also contributes to the elasticity of the walls within the thorax.

Important Histological Characteristics

Histology – The study of the forms of structures as observed under a microscope.

• Due to the relatively high concentration of sulfated glycosaminoglycans that attract basophilic stains, one will notice the extracellular matrix of the hyaline cartilage is generally basophilic.
• The type II collagen fibrils are small and have a refractive index which renders them invisible when using bright-field microscopy. Hence the extracellular matrix appearing smooth and glass-like.
• The organic components within the matrix do not present a uniform distribution. Staining revealing the matrix to be divided into three basic zones:

1. Capsular Matrix – this is a thin zone of matrix that surrounds each lacuna, and has the highest concentration of sulfated glycosaminoglycans.
2. Territorial Matrix – surrounds the capsular matrix
3. Interterritorial Matrix – is less basophilic and PAS-positive thanks to higher concentrations of collagen and a corresponding lower concentration of sulfated glycosaminoglycans.

• Perichondrium covers the cartilage in most places. All excluding the articular and epiphyseal cartilage.

Elastic Cartilage

Elastic cartilage, also known as yellow cartilage, is made up of networks of elastic and collagen fibers of which the principal proteins are elastin. Under the microscope (histologically) elastic cartilage and hyaline cartilage look very similar, other than the many yellow fibers that are found in a solid matrix. These yellow fibers form bundles that provides the elastic cartilage the flexibility that it needs to endure repeated bending. These bundles of fibers also appearing to be darker under a microscope. Elastic cartilage has a high concentration of elastin fibers arranged in an extracellular matrix structure, and unlike hyaline cartilage, it does not calcify for the formation of bones.

Elastic cartilage furthermore boasts the same firmness and resilience of hyaline cartilage, but comes with the added necessity of being highly flexible and elastic. It can be found in joints that are usually associated with movement, and in adult humans, it can be found:

• In the pinna (outer cartilage) of the ear, the external auditory canal and the Eustachian tubes (connecting the nasal passages and the ear)
• The epiglottis (the flap that covers the top of the trachea, preventing food form entering the lungs as you swallow) and cuneiform of the larynx

Important Histological Characteristics

In many regards, elastic cartilage and hyaline cartilage are very similar. There are however some important differences between the two:

• Elastic cartilage has less matrix that hyaline cartilage, this matrix also being infused with elastic fibers
• The matrix of elastic cartilage consists of more type II fibrils as well as having large quantities of branching elastic fibers of varying thicknesses
• The territorial (capsular) cartilage shows thicker bundles of connected elastic fibers, more than that of the interterritorial (intracapsular) cartilage
• Elastic cartilage contains more and larger chondrocytes than the hyaline cartilage. They are more closely packed and only one chondrocyte per lacuna
• All the cartilage is covered by perichondrium
• Exhibits less accumulation of glycogen and lipids than the hyaline cartilage

Main Differences

It should be clear to see that these two forms of cartilage are both one and the same, with a few tweaks and adjustments here and there. They both have an absolutely pivotal role to play in the proper functioning and development of the human body, not to mention being the basis of our entire skeletal structure. Without these building blocks and support structures strategically placed throughout our bodies we would not be functioning as smoothly and as protected as we do.

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