Anatomy 25 cartilage
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What are Costal cartilages?
Cartilages that connect the ribs to the sternum.
What is perichondrium?
Except for joints involving sinovial fluid, cartilage is surrounded by dense irregular connective tissue called perichondrium. Perichondrium is made of dense irregular connective tissue. The perichondrium has blood vessels that supply the cartilage with nutrients. It can produce new cartilage cells ( chondroblasts ) and also kind of helps hold the cartilage together when it is under outward pressure from vertical pressure.
What are the three types of cartilage?
Hyaline, elastic, and firbrocartilage.
Hyaline cartilage is the most common type of cartilage and looks like frosted glass. Its surface is covered with perichondrium. It has sphereical shaped chondrocytes. Hyaline cartilage contains only colagen unit fibril which are very thin rather than larger fibers. Hyaline cartilage makes up the articular cartilage that covers the ends of bone joints. It also forms the cartilage connecting the ribs to the sternum ( costal cartilages ) cartilage in the respiratory structures ( trachea, etc. ) and forms embryonic skeleton.
Elastic cartilage has elastic fibers as well as collagen fibrils running through it. Its surfaces are covered with a perichardium and it appears yellowish colored. It is very bendy cartilage which will retain its shape after bending. Elastic cartilage makes up the outer ear ( pinna ) and the epiglotis ( the flap thing covering your esophagus or trachea ).
- Fibrocartilage is made of layers / rows of thick collagen fibers alternating with rows of chondrocytes.
- Its matrix contains bundles of collagenous fibers.
- It is good at resisting both compression and tension stresses.It does not have a perichondrium covering it. It is found in vertebral discs and articular discs of knee joints.
What is appositional growth in regard to cartilage?
Appositional growth means "growth from outside" and in cartilage means that chondroblasts ( the younger more active cell ) in the perichondrium make new cartilage by secreting new extracellular matrix in layers on top of the original cartilage mass. Cartilage growth stops after teen years.
What is interstitial growth in regard to cartilage?
Interstitial growth is growth from within and in cartilage means that chondrocytes in the cartilage itself divide and secrete new matrix. The new matrixes kind of push each cell away from each other and the cartilage mass expands. Cartilage growth stops after teen years.
Cartilage is made up of two different things in general, what are they?
Cartilage cells - chondrocytes / chondroblasts
Extracellular martix - the stuff outside the cells, ground substance and fibers.
Cartilage Matrix contains fibers, how are these fibers built or put together?
3 polypeptide chains wind around each other to form tropocollagen.
Tropocollagen molecules link up to form collagen fibrils.
A bunch of collagen fibrils link up to form collagen fiber.
A bunch of collagen fibers can even link up to form collagen fiber bundles.
What are elastic fibers made of?
Elastin and microfibrils of fibrillin. Elastic fibers are long and thin and allow tissue with elastic fiber to remain stretchy.
What is the ground substance of cartilage made of?
Glycosaminoglacans ( GAGs ) are long-chained polysacharides that attach to a core protein. They are anionc, negatively charged and hydrophilic, attract water. These GAGs attach to a protein core to form Proteoglycans.
The proteoglycans ( GAGs around a core protein ) are attached to hyaluronic acid, an even bigger mollecule, several of them on an acid, sort of like rows of bottle brushes attached to the acid to form Proteoglycan Aggregates.
The aggregates form linkages with collagen fibrils.
Chondronectin is a protein that links the collagen fibrils to other proteins in the cell membranes of cartilage cells.
What are chondroblasts?
Chondroblasts are young cartilage cells that are formed from mesenchymal ( stem ) cells.
They are very active, secreting extracellular matrix of fibers, ground substance ( GAGs, proteoglycan aggregates, hyaluronic acid, etc. )
When enough extracellular matrix is made the chondroblasts become less active and sit in the lacunae of the cell as a chondrocyte.
What are chondrocytes?
Chondrocytes are former chondroblasts which just kind of sit in the lacunae of the cell.
What is territorial matrix?
It is the extracellular matrix closest to the cell, it is high in GAGs and low in collagen fibrils.
It stains dark in light microscope images.
What is Interterritorial matrix?
Matrix which is further from the cell and has fewer GAGs and more collagen fibrils.
It stains light in light microscope images.
Characteristics of Chondroblasts...
- Increased metabolic rate and secretory activity.
- Well developed golgi, rer, nucleolus.
- Nucleus stains light ( active nucleus, euchromatin ).
- Ovoid cell shape.
- Very prominent territorial matrix.
Characteristics of Chondrocytes.
- Decreased metabolic rate and secretory activity.
- Less prominent golgi, rer, and nucleolus.
- Nucleus darker staining ( inactive condensed chromatin.
- Round cell shape.
- Territorial matrix not as prominent.
What is perichondrium?
The perichondrium is a layer of dense irregular connective ( dic ) tissue that covers the external surfaces of cartilage. When cartilage is compressed, the perichondrium helps keep it in place and prevents it from squishing out.
It is made up of two layers:
The inner / cellular / chondrogenic layer has fewer collagenous fibers and more connective tissue cells. The inner layer also has mesenchymal cells which can become chondroblasts later on.
The outer layer is made of more collagenous fibers and less connective tissue cells.
Cartilage is avascular, this means...
It has no blood vessels running through it.
That means that it has to get its nutrients through different means. Nutrients move from blood vessels in perichondrium outside the cartillage, through the extracelular matrix to the cells. Since the matrix is so dense the diffusion is slow.
Nutrients in joint cartillage is supplied by synovial fluid.
Cartilage also has no nerves.
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