What is Cartilage?
Cartilage is a resistant but elastic and flexible animal tissue that, in the higher vertebrates, covers the surface of the bones at the joints, forms the framework of certain organs (nose, ear) and the skeleton of the embryos.
It is a soft, sometimes elastic connective tissue that is found in animals of different types in the body, including on the surface of joints between the bones and in the rib cage, ear, nose, bronchi or intervertebral discs. The cartilage is formed by rounded cells, the chondrocytes, included in chondroplastes called boxes in an extracellular matrix consisting of glycosaminoglycans and collagen.
Cartilaginous fish
Cartilaginous fish (Chondrichthyes) are one of the main classes of fish with bone fish. It includes sharks and rays whose skeleton is formed of cartilage and not bone.
The mechanical properties of the cartilage
The mechanical properties of cartilage are both supple but resistant, place it in an intermediate position between the bone and less rigid, more or less dense connective tissues such as tendon or muscle. The rigidity of the cartilage gives it a particularly important role in maintaining the opening of the various tubes open to the open air of the body whether it is the trachea, the alar cartilages of the nostrils or the flag of the ear around the ear canal. Compared with other connective tissues, cartilage has the property of not being vascularized or innervated. In case of lesions, their repair is slow or almost non-existent in adults.
Does metabolism work in the production of Cartilage?
Yes, cartilage is produced initially from the division of cells which you can broadly term as a biochemical activity under the heading of ‘metabolism’. However, once the cartilage is damaged, then the regeneration process is very slow and limited.
Once damaged, can cartilage regenerate?
Yes, but not behind a certain limit. To understand this, you will have to understand the process of cartilage production. For this I will start from the embryology. There is a substance called mesenchyme which is derived from mesoderm during the embryonic state. This mesenchyme exists as a combination of the ‘mesenchymal tissues’ (focus on it), serous fluid and other many different tissue proteins. This mesenchyme develops into many systems later in life like the lymphatic and circulatory systems, as well as the musculoskeletal system.
The mesenchymal tissue in the mesenchyme contains mesenchymal stem cells which are highly proliferative in fetal and early life after birth. These mesenchymal stem cells differentiate into chondroblasts (cartilage forming cells). Chondroblasts are a kind of chondrogenic (genic mean ‘generating’) cells which form cartilage by secreting a substance called ‘extracellular matrix’. This extracellular matrix consists of ground substance (proteoglycans and glycosaminoglycans) and associated fibers, such as collagen. The chondroblasts, after secreting extracellular matrix, trap themselves in lacunae which are small spaces that are no longer in contact with the newly created matrix. The chondroblasts is now a chondrocyte, which is usually inactive.
In other words, new chondrocytes have imprisoned them in small chambers where there is no direct blood supply around from blood. These entrapped chondrocytes get a very limited nutrition from the extracellular matrix via diffusion.
Now we come to our main question. Once damaged, cartilage has limited repair capabilities because chondrocytes are now bound in lacunae and cannot migrate to damaged areas. Also, because cartilage does not have a blood supply and chondrocytes (which have to regenerate the new cartilage), have limited nutrition supply from the extracellular matrix, can only deposit very limited ‘new’ extracellular matrix and in a very slow fashion. So, once damaged, cartilage cannot regenerate behind a certain limit. However, there are new techniques in which the cartilage from the other less needed areas of the body can be grafter to the injured area via surgery. Scientist are also working on mesenchymal stem cells to generate cartilage in the damaged area.