CARTILAGE TISSUE: CHARACTERISTICS, COMPONENTS, FUNCTIONS - ANATOMY AND PHYSIOLOGY - 2024

The cartilage tissue or cartilage is a type of connective tissue. Its main constituent is the cartilaginous matrix, which is gelatinous in consistency but highly resistant to pressure. In the matrix there are small cavities or gaps called chondroplasts, where chondrocytes are housed.

Generally, the matrix is ​​surrounded by the perichondrium, which is also made up of connective tissue. The latter is made up of an outer fibrous layer and an inner layer called chondrogens.

Hyaline cartilage (Trachea of ​​a cat). Photograph by: Biophotos. Taken and edited from:

Depending on its constituents, three types of cartilage can be distinguished: hyaline, elastic and fibrous. Each type of cartilage has unique characteristics and functions, and can be found in different parts of the body.

Cartilage tissue is the main constituent of the skeletal system in vertebrate embryos and cartilaginous fish. Likewise, you can develop several diseases, some of them with no known cure and all very painful.

Cartilage has therapeutic properties and is used for direct consumption or through the extraction of chondroitin sulfate. Among the diseases treated with these substances are cataracts, osteoarthritis, urinary tract infections, joint pain and acid reflux, among others.

characteristics

Among the main characteristics of cartilage tissue, the following stand out:

- It is an avascular tissue (that is, it lacks blood vessels). Due to this, its nutrition and gas exchange is by diffusion. The extracellular matrix is ​​abundant; in fact, it can represent about 95% of the total volume of cartilage tissue.

- It has many type II collagen fibers and a large amount of proteoglycans. Due to this, its consistency is similar to that of rubber: flexible but resistant.

- The main cells that constitute it (chondrocytes) are embedded within the extracellular matrix that they secrete themselves.

- It has little regeneration capacity.

Components

Cartilage tissue has two components: one cellular and one extracellular.

Cellular

The cellular component of cartilage is made up of three types of cells: chondroblasts, chondroclasts, and chondrocytes.

Chondroblasts

Chondroblasts are spindle-shaped cells responsible for secreting and maintaining the cartilaginous matrix. They have a large nucleus, one or two nucleoli, and a large number of mitochondria, secretory vesicles, and endoplasmic reticulum.

They also have a well-developed Golgi apparatus and are stained with basic stains. They can originate from chondrogenic cells in the inner layer of the perichondrium, or from mesenchymal cells.

Chondroclasts

They are large and multinucleated cells. Its function is to degrade cartilage during the chondrogenesis process to shape development.

These cells are difficult to detect; some researchers believe that they come from the fusion of several chondroblasts.

Chondrocytes

These are cells derived from chondroblasts. They reproduce by mitosis and are located within the cartilage matrix.

Its main function is to maintain this matrix, producing collagen and proteoglycans. Chondrocytes derived from the same cell are called isogenic groups or chondromas.

Extracellular

The extracellular component of cartilage is represented by the extracellular matrix, which is made up of fibers, proteoglycans, and glycosaminoglycans.

Fibers

They are also called as ground substance. They are composed mainly of type II collagen, which is synthesized by chondroblasts. Its quantity and thickness will depend on the type of cartilaginous tissue and its function is to give resistance to the tissue.

Proteoglycans and glycosaminoglycans

These elements make up the fundamental substance. They are a special class of glycoproteins and their functions in the extracellular matrix include keeping it hydrated, serving as a selective filter, and helping collagen to give tissue strength.

The main constituent in cartilage is chondroitin sulfate, a sulfated glycoprotein.

Histogenesis

Cartilage tissue can develop directly from mesenchymal cells or from the perichondrium. During the formation of the perichondrium, mesenchymal cells differentiate from fibroblasts on the outside of the developing cartilage.

The perichondrium is responsible for growth by apposition and preservation of cartilage. This tissue is made up of a fibrous layer and another called chondrogenic; In this last layer, chondrogenic cells form chondroblasts that will cause cartilage to grow.

In direct development, mesenchymal cells differentiate directly from chondroblasts. These secrete extracellular matrix where they are trapped and divide mitotically, to later transform into chondrocytes.

Chondrocytes derived from the same chondroblasts are called isogenic group. These cells continue to produce extracellular matrix and separate from each other, causing interstitial cartilage growth.

Increase

The growth of cartilage tissue can be of two types: appositional and interstitial.

Growth by apposition

Growth by apposition occurs from the perichondrium. The innermost layer of the perichondrium is called the chondrogenic zone; In this layer, chondrogenic cells transform into chondroblasts.

Chondroblasts mitosis and differentiate into chondrocytes that produce collagen fibrils and fundamental substance. In this case, the growth is from the outside to the inside of the cartilage.

Interstitial growth

This type of growth occurs by mitotic division of the cartilage chondrocytes. The chondrocytes are going to divide towards the center of the cartilage; in this way, this growth occurs from the inside to the outside of the cartilage.

As cartilage ages, the fundamental matrix becomes more rigid and dense. When the matrix is ​​very dense, this type of development in cartilage tissue ceases.

Types

Hyaline cartilage

It is a translucent and homogeneous tissue that is generally surrounded by perichondrium. The cells, called chondrocytes, have a large nucleus located in their center and also have one or two nucleoli.

This cartilage has abundant lipids, glycogen and mucoproteins. Likewise, collagen fibers are very thin and not very abundant.

It presents both types of growth and is found in the joints, the nose, the larynx, the trachea, the bronchi and the epiphyses of developing bones.

It is the fundamental constituent of the skeleton of the developing embryo in vertebrates and is later replaced by bone.

Elastic cartilage

It is surrounded by perichondrium. The cells are spherical and are arranged individually, in pairs or in triads.

The extracellular matrix is ​​scarce and the total fat and glycogen content is low. The territorial matrix forms a thick capsule and, for its part, the collagen fibers are branched and present in great quantity.

This type of cartilage has both types of growth and is a tissue that serves as support and has great flexibility. It can be found in the pinna, external auditory canal, Eustachian tubes, epiglottis, and larynx.

Fibrous cartilage or fibrocartilage

It presents numerous bundles of type I collagen fibers arranged in parallel. It lacks perichondrium and does not show appositional growth, only interstitial.

The extracellular matrix is ​​sparse and the chondrocytes are generally smaller than in the other types of cartilage. These cells are arranged in rows individually or in pairs between the collagen fibers.

It supports strong tractions, therefore it is located in areas where the fabric must withstand pressure and lateral displacement. It is located in the intervertebral discs, in the middle joint of the pubic bones, in the menisci of diarthrosis-type joints and on the edges of the joints, among other areas.

Features

Its main function is to support other organs. In hollow organs or ducts - such as those of the respiratory system (for example: trachea, bronchi) or those of the auditory (auditory canal) - they give shape and support to these, preventing them from collapsing.

Protects the bones in the joints, preventing their wear. Furthermore, in vertebrate embryos - and in some adult organisms such as cartilaginous fish - it forms the skeletal system.

This tissue is the precursor of cartilage bones, or replacement bones, which make up the majority of vertebrate bones.

White shark, Carcharodon carcharias, cartilaginous fish. Taken and edited from: Terry Goss.

Diseases

Recurrent Polychondritis

Recurrent polychondritis is an autoimmune disease first described by Jaksch-Wartenhorst in 1923. It affects cartilage tissue and mainly attacks the cartilage of the nose and ear.

It can also affect the eyes, the cardiovascular system, the tracheal tree, the kidneys, and the joints. The recurrent name refers to the fact that it is recurrent.

The disease works by inflaming and potentially destroying cartilage tissue, and affects people between the ages of 30 and 60, regardless of their gender. Treatment consists of prednisone or methylprednisone and immunosuppressants such as methotrexate.

Osteoarthritis

Osteoarthritis is a disease that affects the joints. It causes the deterioration of the articular cartilage; it also causes proliferation of the bone adjacent to the cartilage and inflammation of the synovium.

Its origin is multifactorial with a strong genetic component in which more than one gene is involved. It is the most common of the rheumatic diseases.

It mainly attacks the elderly. There is currently no treatment to prevent or stop osteoarthritis; the usual procedure is aimed at reducing pain and inflammation.

Costochondritis

Costochondritis is a condition of the costo-sternal cartilage (the joint of the ribs with the sternum). It is very painful and can be mistaken for a heart attack.

It mainly affects young people of both sexes. The cause of the disease is unknown, but it is associated with recurrent cough, excessive physical exertion, and rib and sternum injuries.

The usual treatment consists of anti-inflammatories and medications to reduce pain. The disease usually goes away on its own after a few days to a couple of weeks.

Vertebral herniation

Herniated discs can have different origins; one of these corresponds to the fissures in the cartilage of the vertebral bodies.

The cartilage of the vertebrae covers the upper and lower face of each vertebral body. It is composed of two layers: the outermost is made of fibrous cartilage and the innermost is hyaline cartilage. When cracks occur in the cartilage, the intervertebral disc is deformed and tends to collapse.

Spinal stenosis

Spinal stenosis is a narrowing of the canals that contain the spinal cord and nerve roots. It has multiple causes, among which are aging, tumors, arthritis, hypertrophy of bone and vertebral cartilage.

It represents one of the main causes of pain in the back and lower limbs; however, spinal stenosis can sometimes be painless. The cause of pain is tightness of the spinal cord and nerve roots.

Treatment includes rehabilitation, physical therapy, anti-inflammatories, and pain medications. Surgical intervention may be necessary in some cases.

Achondroplasia

Most of the bones in the human body are originally cartilage that later ossify (replacement bones). Achondroplasia is a disease of genetic origin that prevents the normal change of cartilage to bone.

It is caused by a mutation in the FGFR3 gene and is the main cause of dwarfism. It can also cause macrocephaly, hydrocephalus, and lordosis, among other conditions.

There is no effective treatment for achondroplasia; growth hormone therapy only partially helps. Studies for gene therapies are currently under development.

Benign tumors

Benign bone tumors are different types of tumors that vary in size, location, and aggressiveness.

Histologically they are similar to normal bones. They do not invade neighboring tissues and are benign - that is, they do not endanger the patient's life. However, they are potentially dangerous because they can become malignant.

Their development is slow and they are generally located in the region of the metaphysis, although they can also be located in the epiphysis of the bones. The most common of these tumors are cartilage-forming tumors (chondromas).

Chondrosarcomas

Chondrosarcoma is a malignant tumor that affects the cartilage. It mainly affects people over 40 years of age.

Cartilage-forming cells and undifferentiated cells are found in tumors. This tumor is made up of hyaline cartilage and malignant myxoid.

It attacks the long bones of the limbs, the pelvic girdle and the ribs. It is generally slow to develop and does not metastasize, although there are more aggressive forms. The most recommended treatment is surgical removal of the compromised tissue.

Histopathological image of chondrosarcoma of the chest wall. Taken and edited from: No machine-readable author provided. KGH assumed (based on copyright claims)., via Wikimedia Commons.

Therapeutic uses

Shark cartilage

Shark cartilage is used in alternative medicine for various types of cancer, including Kaposi's sarcoma. It is also used to treat arthritis, retinal damage, and enteritis.

Externally it has been used to treat psoriasis and aid in wound healing. In case of hypercalcemia, it should be used under medical supervision.

Chondroitin sulfate

Chondroitin sulfate is extracted mainly from shark and cow cartilage. It can be used alone or in combination with other compounds, such as manganese ascorbate or glucosamine sulfate.

It comes in the form of drops, ointments, injections, and / or pills. It is used for osteoarthritis, myocardial infarction, heart disease, osteoporosis, psoriasis, dry eyes and osteoarthritis.

References

1. Cartilage. On Wikipedia. Recovered from Wikipedia: en.wikipedia.org
2. Chondroblast. On Wikipedia. Recovered from Wikipedia: en.wikipedia.org
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4. LC Junqueira, J. Carneiro (2015). Basic Histology. Editorial Médica Panamericana, Spain.
5. Y. Krishnan, AJGrodzinsky (2018). Cartilage diseases. Matrix Biology.
6. MI Quenard, M. García-Carrasco, M. Ramos-Casals (2001). Recurrent Polychondritis. Integral Medicine. Recovered from Elsevier: elsevier.es