Or it´s only transitional stage of chondrocytes formation which is separated into a individual cell of chondrocyte later? And why should it separate, whereas it differentiates from a single chondroblast? Couldn´t it just differentiate from a single chondroblast?
I mean, if it´s give rise to isogenic group, what´s the purpose of this formation? What it benefits? Why not stay still in form of an individual cell?
Sorry to keep asking such basic stuffs that an undergraduate should´ve already known well.
Here are some related things to consider.
Cartilage is a peculiar tissue. It is only ca. 10% cells (chondrocytes). So chondocytes are by nature rather isolated.
In comparison, many tissues are mostly cells.
Also, the dense cross-linked, osmotic pressure-driven structure of cartilage makes it almost impossible for chondrocytes to migrate--i.e. go to some location of cartilage damage and form more cartilage.
Finally, chondrocytes have no blood supply. There are no blood vessels within articular cartilage, only below it in the bone. Chondrocytes get their nutrition and dispose of waste via synovial fluid.
All this means that articular chondrocytes are not very active cells, and articular cartilage is not readily repaired. It is amazing to me that articular cartilage survives joint motion wear and tear as long as it does.
Dear Tiko,
Interstitial growth occurs inside the cartilage, where the chondrocytes proliferate. After proliferation, the cell can not go anywhere, as the matrix is hard, so they form cluster of cells that you call the isogenic cells. Chondrocyte clusters from interstitial growth do not come from chondroblast, as chondroblasts are located on the surface of a cartilage, not inside a cartilage.
Another growth is from the periphery (aposisional growth), Chondrogenic cells in the perichondrium differentiate into chondroblasts at the surface of a cartilage. The chondroblasts secrete matrix, and when they are surrounded by matrix, they become chondrocytes that still have proliferation capacity. So, only one chondrocyte in a cluster is derived from a chondroblast that was .previously located at the surface.
So, chondroblast is on the surface of a cartilage, and chondrocyte is inside the cartilage.
@Pawitan certainly has it right, except I disagree with her description of cartilage as "hard." It is not. For example, it is easily indented at any scale at slow indentation rates.
However it is densely cross-linked and its water content is tightly bound by ionic-osmotic forces. Under simple mechanical pressure with porous platens, it takes hours to force much water out of cartilage.
Also, cartilage is viscoelastic, and its dynamic aggregate structural modulus is highly sensitive to strain rate. At high strain rates cartilage is stiff (not hard), giving it the ability to protect underlying bone from damage due to impact (high strain rate) loads. Conversely, at low strain rates is not very stiff, and flexes and compresses a bit under load. This allows some transfer of fluids in and out for chondrocyte nutrition and removal of waste products.
Dear @ Daniels,
Thanks for the correction. Yes, it is stiff, not hard, because bone is hard.
The cartilage grows by two processes. One is from the perichondrium through the differentiation of mesenchymal cells (appositional growth) and another occurs primarily in young cartilage, starting from chondrocytes surrounded by the cartilage matrix (interstitial growth). In the interstitial growth, the newly formed cells detach because the matrix is more hydrated, malleable and thus easy to expand, as it has type II collagen fibrils. With aging there are more type I collagen fibers, which are more rigid than type II collagen fibers, making it difficult for the newly formed cells to separate. Thus, with a more rigid cartilage, isogenic groups appear at a more frequency.
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