Welcome to the wonderful world of histology. Histology is how we study the human body on the cellular level. Tissue can be classified into four different types: Epithelial, connective, nerve, and muscle tissue. This week we are continuing to look at connective tissue. Connective tissue can further be divided into hard and soft connective tissue.
Evolutionary cartilage is the first hard connective tissue. We see entire skeletons made up of it when we look back down the evolutionary tree. Sharks still have this to this day. Cartilage is strong but not as strong as bone. With more forces at play, the cartilage became mineralised and then eventually bone.
Bone and cartilage have always been interlinked. Our long bones start out life as cartilage before becoming bone. Even as we grow through childhood our growth plates are cartilage that then turns into bone when we become adults.
Cartilage itself plays a role that bone cannot. Cartilage can be compressed, it can be stretched and deals better with shearing forces. Cartilage can be found in every joint in our body and strengthens many more structures.
Every tube and every sphere in the body has trouble with surface tension, meaning without aid the tubes and spheres want to stick to each other and never open again. Cartilage solves this problem by wedging the airway open in c shape bands and shunting the bladder into shape with the triangular wedge that is the trigone. The cartilage that does this along with capping the joints is hyaline cartilage.
Cartilage consists of a large amount of extracellular material. In ratio to its cells, there is a large number of collagen fibrils, proteoglycans, and hyaluronic acids. This matrix surrounds the chondrocyte cells. Giving the appearance that the chondrocytes are bubbles of cells trapped in the matrix.
Hyaline cartilage can be modified to form two additional types of cartilage. Elastic cartilage is the type of cartilage found in the ear and epiglottis. An additional dense network of crossed-linked elastin fibres makes elastic cartilage more flexible and hyaline. Fibrocartilage can be found where tendon meets bone, the discs of the spine, and part of the pubic symphysis (the joint between the two halves of the pelvis). With this type of cartilage, there are much more matrix and collagen bundles and fewer chondrocytes.
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