HYALINE CARTILAGE: CHARACTERISTICS, HISTOLOGY, TYPES AND FUNCTIONS - ANATOMY AND PHYSIOLOGY - 2025

The hyaline cartilage is a type of cartilaginous tissue containing chondrocytes abundance and morfa substance consists of collagen fibers very thin and slim. It also contains a large amount of lipids, glycogen and mucoproteins. It is the most common and abundant type of cartilage tissue.

Hyaline cartilage is formed during embryonic development, constituting the skeleton of the embryo. Later it is almost entirely replaced by bone tissue, persisting only in some regions such as the synovial joint, the nasal septum, the distal part of the ribs and also in the trachea and larynx.

Optical micrograph of hyaline cartilage of trachea. Taken and edited from: Ganymede.

Its growth occurs both by apposition and by interstitial growth. Depending on its location, in the adult body we can speak of articular and non-articular hyaline cartilage.

In addition to serving as a template for the development of replacement bone, hyaline cartilage has other important functions, such as impact protection or reduction of friction in the joints.

characteristics

Hyaline cartilage contains a single type of cells made up of chondrocytes, while the matrix is ​​made up mainly of type II collagen fibers and chondroitin sulfate.

The name hyaline comes from the pearly coloration of the fabric and its appearance that resembles a frosted crystal.

The hyaline carilaginous tissue is generally covered by perichondrium, a fibrous layer of connective tissue that provides nutrients to the cartilage that is not vascularized or has nerve endings.

Histology

Hyaline cartilage tissue is made up of two components, one cellular and the other extracellular or matrix, which are surrounded by the perichondrium.

- Perichondrium

It is a very dense sheet of connective tissue that will cover the cartilage with the exception of those areas where the cartilage is immediately under the skin, such as in the ears or nose, as well as at the joint ends. The perichondrium is made up of two layers:

Fibrous layer

It is the outermost. In it, the mesenchymal cells differentiate into fibrocytes. This is a highly vascularized layer, being responsible for the nutrition of the chondrocytes.

Chondrogenic layer

In this layer, the mesenchymal cells differentiate into chondroblasts, which are responsible for growing cartilage in a form of growth called apposition. Only chondrocytes are found in mature hyaline cartilage.

- Matrix or fundamental substance

The ground substance, which is the extracellular matrix, is made up of a morpho and an amorphous ground substance. In mature hyaline cartilage it appears as a homogeneous structure that acquires a slight bluish color.

The fundamental matrix surrounds the chondrocytes that are contained in spaces called lacunae.

Morpho ground substance

In the case of hyaline cartilage, the morpho ground substance is almost exclusively made up of thin type II collagen fibers, which are not very abundant. These fibers are responsible for the strength of the fabric.

Amorphous ground substance

The main component of the amorphous substance in hyaline cartilage is represented by proteoglycans. These are a form of glycoprotein that consist of a protein core attached to long polymers of carbohydrates, receiving the name of glycosaminoglycans.

- Chondrocytes

They are the only type of cells present in mature cartilage. Cells are rounded or blunt-angled that originate from the perichondrium. These have a large central nucleus and generally one or two nucleoli. They also have fats, mucoproteins and sugars in the form of glycogen.

In the areas closest to the perichondrium, chondrocytes are more dispersed and located in individual lagoons. But as you go deeper into the cartilage, the cells are more densely distributed and in pairs or tetrads called isogenic groups.

Increase

With the exception of the hyaline cartilaginous tissue areas, where perichondrium is not present, this tissue shows both appositional and interstitial growth. In the first case it will only be of the interstitial type.

Due to these two types of growth, in a histological section of the mature hyaline cartilage, the matrix will appear more dense towards the interior of the tissue than towards the periphery.

By apposition

It occurs when chondrocytes form in the chondrogenic layer of the perichondrium from the chondroblasts, which will be added to the mature hyaline cartilage to increase its volume. This growth occurs from the peripheral zone of the cartilage, towards the interior of it.

Interstitial growth

Growth in this case occurs by mitotic divisions of chondrocytes located in individual lacunae, resulting in groups of two or four cells from the original chondrocyte. For this reason, these groups of cells are called isogenic groups.

This type of growth, in contrast to appositional growth, will then occur from the inside of the tissue to the outside.

Types

Articular cartilage

It is characterized by the lack of a perichondrium. It appears as a thin layer of tissue at the articular ends of the bones, specifically in the synovial cavity, preventing direct contact between the bones and its consequent wear by friction.

In this type of tissue, collagen fibers represent more than half of its dry weight and are responsible for the integrity of the tissue. In addition to preventing frictional wear and making it easier to move, they also help cushion excess weight.

Articular hyaline cartilage. Taken and edited from: Eugenio Fernández Pruna.

Non-articular cartilage

Non-articular hyaline cartilage occurs in different parts of the body, such as the larynx, pharynx, and the ends of the ribs, where it fulfills different functions, mainly to provide structural support.

Features

Support

Hyaline cartilage provides elastic support to the structures where it is located. For example, in the walls of the trachea the presence of arches formed by this tissue prevent its collapse. In the nose, it prevents the closure of the nasal vestibule and contributes to the proper functioning of nasal breathing.

Friction reduction

The smooth surface of the cartilaginous tissue that lines the joints helps the bones slide when they move, reducing friction and, therefore, wear and tear on them. The synovial fluid also participates in reducing friction by lubricating the cartilage.

Shock absorption

Due to its flexibility and resistance, hyaline cartilage tissue is capable of cushioning impacts and reducing the effects of being overweight on the bones, a function of great importance mainly in the joint areas.

The amorphous substance of the hyaline tissue is, to a large extent, responsible for this shock-absorbing capacity because, due to its chemical constitution, it is capable of acquiring and retaining large concentrations of water.

Skeletal

The hyaline cartilage tissue is responsible for forming the temporary skeleton of the embryo, which will then be replaced by cartilage bone or replacement bone.

Increase

The long bones of the body can maintain their increase in length as the body grows due to the interstitial growth of the hyaline cartilage in the epiphyseal plate.

Hyaline cartilage and bone replacement

During embryonic development, the hyaline cartilage will form the skeleton of the embryo. This skeleton is temporary and later in development it will be replaced by cartilage bone, also called replacement bone or endochondral bone.

In the first place, the mesenchymal cells are going to be arranged in the form of parallel sheets and become perichondrium that will form the cartilage tissue precursor of the bone. Later, the perichondrium will form chondroclasts that will be responsible for destroying the preformed cartilage.

Then, the perichondrium will be replaced by periosteum that will produce osteoblasts, which will deposit inorganic calcium salts in the extracellular matrix to calcify the cartilage.

In the bone in formation, three regions of ossification will be differentiated: the diaphysis or middle part and the epiphyses, at the ends. Among them you will find the metaphysis or epiphyseal plate. The replacement of cartilage by bone begins in the diaphysis and subsequently continues in the epiphyses.

The calcium salts form a barrier that prevents the chondrocytes from carrying out gas and nutrient exchange with the superficial layer of cartilage, for which they will die.

The calcified cartilage is then vascularized and the blood vessels contribute to erode the cartilage remains to begin the formation of the medullary cavity.

The last area to calcify is the epiphyseal plate, and as long as this ossification does not occur, the cartilaginous tissue will proliferate in this area. This interstitial growth of cartilage is responsible for the lengthening of bones. Once the epiphyseal plate is calcified, this type of growth in the long bones ceases.

Articular cartilage injuries

Articular cartilage is 2-4 mm thick; Due to age or pathological conditions (obesity, hormonal alterations), this tissue can stop growing and regenerate causing osteoarthritis.

Articular cartilage tissue injuries are difficult to repair due to the poor ability of chondrocytes to migrate to repair injuries, as this cartilage does not have blood supply.

To prevent this type of injury, it is advisable to avoid being overweight, as well as to perform low-impact exercises such as walking, cycling or swimming. In severe cases, the injuries can be treated surgically.

References

1. LC Junqueira, J. Carneiro (2015). Basic Histology. Editorial Médica Panamericana, Spain.
2. PR Weather, HG Burkitt & VG Daniels (1987). Functional Histology. 2 ^nd edition. Churchill Linvingstone.
3. KV Kardong (2006). Vertebrates: Comparative anatomy, function, evolution, The McGraw-Hills Companies, Inc.
4. Cartilage. On Wikipedia. Recovered from en.wikipedia.org.
5. Hyaline cartilage. On Wikipedia. Recovered from en.wikipedia.org
6. Animal tissues. Connective. Hyaline cartilage. In Atlas of Animal and Plant Histology. Recovered from mmegias.webs.uvigo.es
7. C. Lira (2019). Cartilage tissue: characteristics, components, functions. Recovered from lifeder.com.