cartilages

cartilage injuries

Because cartilage is avascular and aging choncrocytes lose their ability to divide, cartilage heals slowly when injured. This is why sports injuries involving damage to cartilage take so long to heal. During later life, cartilage tends to calcify or even ossify (become bony). This causes the chondrocytes to die because diffusion of oxygen and nutrients is eliminated.

cartilage growth

Cartilage and bone grow in two ways: by adding onto the surface called appositional growth, and by growing from within called interstitial growth.

elastic cartilage CT structure

Elastic cartilage has a much more restricted distribution. It appears yellow when fresh. The organic matrix of elastic cartilage contains less ground substance and is filled with elastic fibers. As we learned previously, elastic fibers branch. In elastic cartilage they form a network within the matrix which can be visualized using a microscope because the matrix does not appear smooth and glassy. In the picture above, the fibers appear purple to black. This is because a special stain was you so they can be seen. Another distinguishing histological feature of elastic cartilage is that the chrondrocytes are more abundant and more closely packed compared to hyaline cartilage.

cartilage classes

Hyaline cartilage Elastic cartilage Fibrocartilage

cartilage structure

Withstands both tension and compression Tough but flexible Provides a resilient rigidity to the structures it supports. Lacks nerves (Not innervated) Avascular (without blood vessels) Receives nutrients via diffusion from CT surrounding it (perichondrium). Cartilage matrix is about 80% water The ground substance contains large amounts of the GAGs chrondroitin sulfate and hyaluronic acid, and fibers of collagen and sometime elastin.

osseous CT location

bones

osseous CT fn

Besides functioning to support and protect the body and some of its vital organs by enclosing , bone forms the levers upon which muscle acts to create movement. Bone also functions as a major storage site particularly for calcium, therefore bone plays a primary role in calcium homeostasis. There are other vital minerals stored in bone as well. Some bones store adipose tissue in their marrow cavities which functions as an energy reserve. Other bones have sites in their marrow cavities for the production of both red and white blood cells, a process called hematopoiesis.

osseous CT structure

Bone comes in two forms, spongy and compact. Regardless, the mature cells of bone are called osteocytes and they are found in lacunae just like cartilage. Hard, calcified matrix containing fibers Osteocytes lie in lacunae Very well vascularized The histological section shown in the picture above is of compact bone. The osteocytes are the tiny cells that somewhat resembles ants because of the appearance of fine lines leaving the main cell body. The fine lines are actually extensions of the cytoplasm that lie in tiny channels called canaliculi. They keep the osteocytes connected to one another and to a nearby blood supply. Recall that the matrix is calcified and so prevents diffusion.

osseous CT structure

Bone or osseous tissue is a very special kind of connective tissue. The matrix contains very little ground substance and the GAG is chondroitin sulfate. Over 90% of the matrix is made up of collagen which makes bone very strong. Packed around the collagen fibers are small crystals of calcium phosphate salt called hydroxyapatite. The crystals make bone hard; if chemically decalcified bone can be tied in a knot. Unlike cartilage, bone is highly vascularized. This is because, the hydroxyapatite crystals impede diffusion of nutrients to the bone cells. Just like cartilage, most of the bone is covered by a dense irregular connective tissue carrying blood vessels and nerves. In bone, this layer is called the periosteum.

elastic cartilage location

Elastic cartilage is found where support is required, but the structure is subject to distortion. For example, you can twist and turn your outer ear called the pinna, but it will spring back to its original shape. Elastic cartilage is also found comprising some of the cartilages of the larynx. epiglottis

fibrocartilage location

Examples of locations in the body where fibrocartilage is found included the cartilages (discs)of the knee joint (menisci), intervertebral discs which are cushions between the vertebrae, and the cartilage between the two pubic bones (pubic symphysis).

fibrocartilage CT fn

Fibrocartilage is found where strong support and ability to withstand heavy pressure are required. Tensile strength with the ability to absorb compressive shock

fibrocartilage CT sturcture

Fibrocartilage is intermediate in structure between hyaline cartilage and dense regular connective tissue. Thick collagen fibers predominate It does not have much ground substance, instead the matrix is paced with dense collage fibers arranged in parallel bundles. The chondrocytes are located in rows between the collagen bundles.

hyaline cartilage location

Forms most of the embryonic skeleton Covers the ends of long bones in joint cavities Forms costal cartilages of the ribs Cartilages of the nose, trachea, larynx It covers the ends of long bones in joint cavities, it is found on the ends of the ribs that join the sternum, it supports the trachea, nose and most of the voice box or larynx. Most of the fetal skeleton forms from a hyaline cartilage model that is eventually replaced by bone.

appositional growth

In appositional growth, stem cells in the perichondrium divide mitotically (make an identical copy of themselves). One of the daughter cells stays a stem cell in the perichondrium, the other matures into an immature chondrocyte (more appropriately, a chondroblast). The imature chondrocytes begin secreting new matrix (shown in dark blue in the diagram). As more and more matrix is secreted, the young chondrocytes are displaced from the surface and are now mature chondrocytes.

interstitial growth

Interstitial growth involves cell division of mature chondrocytes within the matrix. The chondrocyte divides mitotically in its lacuna. This time, both daughter cells remain as chondrocytes. As they secrete additional matrix, they move apart expanding the cartilage from within. This explains why it is common to see clusters of 2-4 chondrocytes together—they are essentially all clones.

elastic cartilage CT fn

Maintains a strucutre while allowing great flexibility

hyaline cartilage CT

Of all three types of cartilage, hyaline cartilage is the most abundant and wide spread. Hyaline cartilage appears glassy, shinny, and whitish-blue when fresh. Amorpous but firm matrix Collagen fibers form an imperceptible network Chondroblasts produce the matrix When mature chodrocytes lie in lacunae About 40% of the matrix is comprised of collagen fibers which give it strenght, but they are fine and indistinguishable. The remainder of the matrix is ground substance. The primary proteoglycan of the ground substance is chondroitin sulfate.

hyaline cartilage fn

Supprots n reinforces Has resiliant cushioning properties Resists compressive stress Hyaline cartilage is the main type of cartilage found supporting and reinforcing body structures and joints.

cartilage cells

The cells of cartilage are called chondrocytes. They may occur singly or in clusters of 2-4 cells. The chondrocytes sit in "holes" in the organic matrix called lacunae . As the chondrocytes secrete the fibers and ground substance of the cartilage, they become trapped in the matrix. Therefore, when they divide they form clusters or nests of cells surrounded by extracellular matrix. Each cluster of chondrocytes represents the descendents of a single chrondrocyte. Unlike other connective tissues, cartilage has no blood vessels or nerves within it. Chondrocytes receive nutrients and oxygen via diffusion through the matrix from the perichondrium. There are three major types of cartilage, hyaline, elastic and fibrocartilage, so named because of the main type of fibers in the matrix.

cartilage damage n age

The pictures on this slide demonstrate various stages and cartilage damage and repair. In figure (a), most of the cartilage is normal as evidenced by its smooth, glistening appearance. The two arrows point out cartilage erosion on the medial humeral condyle. Picture (b) shows cartilage ulceration (arrow) on the medial femoral condyle. c: shows evidence of cartilage repair (arrow) of the medial femoral condyle. Notice that even though the cartilage was repair, the surface is not as smooth as in the surrounding undamaged regions Picture (d) shows Marginal osteophytes (arrows) on processus anconeus of ulna. Osteophytes are bone spurs and they are indicative of damage to the joint surface leading to the onset of arthritis. These develop with age as well as with repeated injury to the joint as a result of cartilage ossification. And yes, they are painful!

cartilage function

Think about your trachea or windpipe. It is comprised largely of cartilaginous rings. These prevent the collapse of the windpipe when you take a deep breath, but also permits the neck to be flexible. The cartilage located on the ends of bones absorbs and cushions the compression when we jump, and allows bones in our joints to glide smoothly when we move. , which enables cartilage to rebound after being compressed, and provides a means of diffusion of nutrients to the cartilage cells.