Flashcards in Cartilage And Endochondral Ossification Deck (15):
What is cartilage composed of?
• Avascular (no blood supply) CT
• Extracellular matrix with chondrocytes
• Chondrocytes: produce and maintain the extracellular matrix
• Large ratio of glycosaminoglycans (GAG’s) to type II collagen in the cartilage matrix permits ready diffusion of substances between the chondrocytes and blood vessels in surrounding cartilage
• Extracellular matrix: solid and firm but pliable. Resilient to repeated application of pressure (large amount of hyaluronic acid, transient movement of water and highly hydrated).
Describe the structure of a proteoglycan
• Core protein joined with 100 GAG’s
• Hyaluronic acid molecules form linear aggregates, each has many proteoglycan monomers
• These molecules are interwoven with a network of collagen fibrils
• The high density of negative charges on GAG’s attracts water forming a hydrated gel
What are the three types of cartilage?
1. Hyaline cartilage – a matrix containing proteoglycans, hyaluronic acid and type II collagen. The hyaluronate proteoglycan aggregates are bound to the fine collagen matrix fibres
2. Elastic cartilage –Type II collagen and elastic fibres. Has a matrix like that of hyaline cartilage but with the addition of many elastic fibres and elastic lamellae
3. Fibrocartilage – Abundant type I collagen fibres and a matrix material of hyaline cartilage
How are the chondrocytes present in hyaline cartilage?
• Present singly or, if recently divided, as small clusters (isogenous groups)
• The chondrocytes within the isogenous groups separate as they elaborate (lay down) extracellular matrix.
Which type of cartilage is the precursor model for bones that develop by endochondral Ossification?
How does hyaline cartilage form long bones?
Ossifies/ mineralises to form bone
• As long bones develop some hyaline cartilage remains at the articulating surface (surface that makes normal direct contact with another skeletal structure as part of a synovial joint) and also at the epiphyseal plate until growth ceases.
Where is hyaline cartilage located?
Hyaline cartilage is sited at articulating surfaces, in parts of the rib cage, nose, and in the trachea, bronchi and larynx.
What is perichondrium?
• Dense CT
• Covers the margin of hyaline cartilage.
• Contains many elongate, fibroblast-like cells which can develop into chondroblasts and thereafter into chondrocytes.
• The fibroblast-like cells of the perichondrium give rise to flat, newly formed chondroblasts, which secrete matrix components and round up to develop into chondrocytes.
• The cartilage grows as a result. This growth from the periphery is known as appositional growth.
What is appositional growth?
- The fibroblast-like cells of the perichondrium give rise to flat, newly formed chondroblasts, which secrete matrix components and round up to develop into chondrocytes.
- The cartilage therefore grows from the periphery
What is interstitial growth?
Chondrocytes deeper in the cartilage may divide and give rise to isogenous groups. Deposition of further matrix by these isogenous groups results in interstitial growth. The cells of the isogenous group separate as they lay down further matrix.
What is elastic cartilage?
• The presence of many elastic fibres in the extracellular matrix confers elasticity upon the cartilage, in addition to the resilience characteristic of hyaline cartilage.
• Unlike hyaline cartilage which calcifies with ageing, elastic cartilage does not calcify.
Where can elastic cartilage be found?
Elastic cartilage is found in the external ear (pinna), in the external acoustic meatus, in the epiglottis, and in the Eustachian tube.
What is fibrocartilage?
• Cell types: Predominantly chondrocytes and some fibroblasts
• Fibrocartilage is a combination of dense regular connective tissue and hyaline cartilage.
• The cells are often seen to be distributed in rows.
• There is no surrounding perichondrium.
• The fibrocartilage has the resilience to act as a shock absorber and to resist shearing forces.
• Rounded chondrocytes tend to be arranged in rows or isogenous groups
Where can fibrocartilage be found?
Fibrocaritlage is present in annulus fibrosis, intervertebral discs, articular discs of the sternoclavicular and temporomandibular joints, the menisci of the knee joint and in the pubic symphysis.