Describe the features of cartilage in general.

• Made up of: (1) cells, (2) fibers, (3) ground substance

• All types contain type II collagen

• embedded within the matrix in lacunae (small compartments)

• Its ECM has a firm, “rubbery” consistency

– Can bear mechanical stress w/o perm. distortion

• cartilage matrix has high water content, is resilient, and acts as a shock-absorber

• cartilage has NO BLOOD SUPPLY, no nerve supply, no lymphatic drainage

• cartilage receives nutrients and oxygen from vessels located in surrounding dense CT – the perichondrium

Explain how hyaline cartilage is an adaptation of the general features:

[image]

Description:

– most widespread type of cartilage in the body
– fresh hyaline cartilage has a glassy appearance: bluish-white and translucent

Location:

– covers articular surfaces of bones in synovial joints
– forms skeleton of nose, larynx, trachea, bronchi

– forms costal cartilages and epiphyseal plates

Features:

• contains type II collagen
• ground substance is hydrated gel of aggregated
proteoglycans and structural glycoproteins:

– e.g. chondronectin – binds to GAGs, collagen type II and integrins

• the matrix is basophilic (sulfated GAGs)

– the “territorial matrix” (zone surrounding lacunae) is richer in sulfated GAGs and so stains darker

• peripheral chondrocytes tend to be elongated, those deeper in the matrix are more rounded
• each chondrocyte is found within a lacuna

• chondrocytes secrete cartilage matrix

– as the cells in an isogenous group continue to secrete matrix, they gradually separate and move away from the others, ending up in their own lacuna
– the secretion of matrix between lacunae within the cartilage is termed interstitial matrix deposition

(+) growth hormone, thyroxin and testosterone

- GH acts on chondrocytes via IGF-1

(-) cortisone, hydrocortisone and estradiol

• Since non-vascular, oxygen tension w/in the matrix is low – chondrocytes metabolize glucose by glycolysis, producing lactic acid.

- Can't be very thick due to non-vascularity

• Compression/decompression of the matrix provides pumping action which moves water and nutrients through the matrix

Explain how elastic cartilage is an adapation of the general features of cartilage.

[image]

Description

– yellowish in color, due to presence of elastin
– often continuous with hyaline cartilage
– surrounded by perichondrium
– Locations:
• auricle of ear, external auditory canal, pharyngotympanic tube

• epiglottis and cuneiform cartilages of the larynx

– Features:
• similar to hyaline cartilage
• contains elastic fibers in addition to type II collagen
fibers

Explalin how fibrocartilage is an adaptation of the general features.

[image]

Description:

– an intermediate between dense CT and hyaline cartilage
– associated with dense CT – no clear boundary b/w them
– no distinct perichondrium

Location:

– found in intervertebral discs, attachments of
some ligaments, pubic symphysis

Features:

• Abundant type I collagen in addition to type II
• type I collagen fibers in irregular or parallel bundles
• contains less proteoglycans than other types of
cartilage – matrix more acidophilic
• contains some elastic fibers

• can occur singly or in isogenous groups
• are typically elongated (following the direction of the
collagen bundles)

Explain cartilage growth.

• chondrogenesis

– cartilage derives from embryonic mesenchyme

– as cartilage develops, mesenchymal cell morphology changes:

• cells round up, lose their cytoplasmic extensions,
multiply, form condensations
• mesenchymal cells differentiate into chondroblasts

– have abundant ribosomes, so are basophilic

• cartilage development is centrifugal

– mature chondrocytes in center, chondroblasts at periphery, superficial mesenchyme develops into perichondrium

Types

– interstitial growth
• due to mitotic division of chondrocytes within cartilage
matrix:  “growth from within the matrix”
• occurs during embryologic development, and in
epiphyseal plates and articular cartilage
– appositional growth
• due to differentiation of chondroblasts from
perichondrium
• new matrix added to the surface of cartilage matrix
• primary type of postnatal cartilage growth

Explain cartilage regeneration.

What is perichondrium and which two (2) cartilage types does it surround?

• surrounds all hyaline cartilage (except
articular cartilage) and elastic cartilage
• formed of type I collagen and fibroblasts (dense irregular CT)
• 2layers

– superficial/fibrous layer contains the type I
collagen and fibroblasts (more fibrous)

– deep/chondrogenic layer contains chondroblast
precursor cells (chondrogenic cells)