CT Cartilage Flashcards
What are the 3 types of cartilage and on what basis are they classified?
- HYALINE CARTILAGE
- ELASTIC CARTILAGE
- FIRBOCARTILAGE
!! based on quality and relative quantity of fibers and ground substance
General functions of cartilage (5)
-specialised CT
-shock absorbing to bear mechanical stress
-forms supporting frameowrk of some organs
-lines articular surfaces
-forms template for growth and development of bones
What are the 2 properties of cartilage and what molecules are responsible for them?
- Tensile strength: collagen fibers in ECM
- Swelling/Elasticity: proteoglycans water absorption
What is an important characteristic of cartilage and the consequences of this (3)
- NOT vascularised or innervated, NO lymphatic vessels
- Nutrients need to be supplied from perichondrium
CONSEQUENCES:
1. low metabolic rate
2. reduced thickness
3.poor healing abilities
What are the specific cell types of cartilage + description of each
- CHONDROBLASTS: immature cells, found in the chondrogenic layer (boundary of the perichondrium and cartilage. Differentiate into chondrocytes
- CHONDROCYTES: Mature cells (differentiate from chondroblasts), located in matrix enclosed within lacunae, clustered into isogenic groups. Secrete components on ECM
- FIBROBLASTS: loacted in the perochondrium (made of dense CT)
What is the general composition of cartilage?
95% ECM (highly specialised): contains WATER, collagen molecules, proteoglycan aggregates, multiadhesive glycoproteins
5% cells: chondroblasts, chondrocytes, fibroblasts
perichondrium: fibrous covering of dense CT
What feature characterises the perichondrium
the flattened nuclei of the fibroblasts
What is the morphology of chondrocytes microscopically?
-abundant RER and Golgi because they produce and secrete proteins (mainly proteoglycans)
-covered with secretory granules and vesicles
Characteristics of hyaline cartilage and locations
-collagen 2 fibers (but scarce amount)
-aggrecan monomers
-homogeneous amorphous matrix
-called GLASSY bcos it is transclucent as it has high amount of ground substances
-resists compressive stresses
-limited healing capacity
LOCATION: ribs/articulations (lubricatoin)/trachea/ larynx/bronchi (prevents collapse) –> PRESENT IN FETAL SKELETON
Specific type of proteoglycan aggregate in hyaline cartilage
USES 3 types of GAGs: hyaluronan, chondroitin sulfate and keratan sulfate
-CS and KS join onto core protein (hyaluronan)
-main monomer = AGGRECAN
other less abundant types: decorin, biglycan and fibromodulin) –> DO NOT MAKE AGGREGATES
What is the main function of the proteoglycan aggregates?
negative charge and a high affinity to water molcules: responsible for swelling and elasticity (cartilage resilience)
Cartilage resillience def
allows cartilage to bear stress without permanent distortion.
-upon stress, proteoglycans release H2O
-when stress is removed the water rebinds to proteoglycans
Structure and role of the multiadhesive GPs
-non collagenous and non proteoglycan linked
-influence interactions between matrix and chondrocytes
EXAMPLES: anchorin, tenascin, fibronectin, chondronectin)
What is the clinical application of analysing multiadhesive GPs?
Indicates cartilage turnover/degeneration: rate at which the cartilage is degraded (present in certain pathologies like osteoporosis)
Organisation of chondrocytes
-contained in clusters (of 2-4 cells) named isogenous groups
-occurs due to the secreted products of the ECM surrounding the cells and isolating them
CONTAIN 3 LAYERS: (iinermost to outermost)
- CAPSULAR MATRIX: highest sulfation due to proteoglycans, has collagen type 6. MOST basophilic
- TERRITORIAL MATRIX: network of collagen type 2, lower sufation. basophilic but not as much as 1.
- INTERTERRITORIAL MATRIX: higher abundance of collagen, no proteoglycans, surrounds territorial matrix. ACIDOPHILIC
Peocess of chondrogenesis (4 STEPS)
- Mesenchymal stem cells in embryonic tissue differentiate into early chondroblasts (rounded)
- Mitosis of chondroblasts and secretion of matrix whixh separates the cells
- Differentiation into chondrocytes and entrapment in lacunae
- Chondrocytes form isogenous groups surrounded by a condensed territorial matrix
2 types of cartilagenous growth:
- APPOSITIONAL: formation on the surface
- cells derived from inner portion of perichondrium
-differentiate into chondroblasts and secrete ECM
-new fibroblasts produced to maintain cell pop. of perichondrium - INTERSTITIAL: formation within existing mass
-caused by mitotic division of existing chondrocytes (within their lacunae)
-daughter cells produced originally share same lacunae but then form a partition
-ECM sythesis and secretion segragates cells even further apart
Where can appositional growth NOT occur
articulations and other sites where the prochondrium is NOT present
Characteristics of elastic cartilage and locations
-elastic fibers in matrix (denser bundles next to chondrocytes)
-collagen type 2
-contains perichondrium
-continuous growth throughout life bcos it is subject to gravity (pulled down)
LOCATION: external ear, auditory tubes, epiglotis
Characteristics and and location of fibrocartilage
-collagen type 1
-NO perichondrium
-cells in row arragement
-good for mechanical stresses
!! more acidophilic bcos there are less abundant proteoglycans
LOCATION: pubic symphysis, intervertebral discs, menisci
Function and morphology of articular cartilage
FUNCTIONS: provides optimal surfaces for enabling movement by preventing friction and transmitting loads to underlying bone
4 LAYERS PRESENT: outermost to innermost
- Tangental zone: flattened chondrocytes, collagen type 2 fibers parallel to free surface
- Transitional zone: random chondrocyte distribution, less organised collagen
- Radial zone: small chondrocytes in columns (90 degree to free surface), colalgen fibers positioned between columns
! separated by tidemark (undulating calcified line)
- Calcified cartilage: small chondrocytes, calcified matrix
!! separated by cement line
- SUBCHONDRAL BONE
How can you distinguish between hyaline and articular cartilage microscopically?
articular C doesnt have a perichondrium and hyaline does
Whatis the clinical importance of articular cartilage?
calcification during aging is common (especially in ribs) which causes degenerative pathologies
OSTEOARTHRITIS: loss of joint mobility and function
Epiphyseal cartilage morphology
-located between epiphysis and diaphysis of long bones
LAYERS:
- RESTING ZONE: chondrocytes unable to proliferate
- PROLIFERATION ZONE: heavy chondrocyte division
- HYPERTROPHIC ZONE: accummulation of lipids and glycogen (which causes cells to enlarge)
- CALCIFICATION ZONE: calcified ECM, cartilage cells die
- OSSIFICATION ZONE: replacement of deteriorating cartilage cells into newly synthesised bone by osteoclasts
What is the process of cartilage repair?
-SLOW AND INCOMPLETE: due to low metabolic rate (due to avascularity)
-action through IGF1 (insulin-like growth factor) secreted by anterior pituitary
-stimulated proliferation of chondroblasts and chondrocytes
-leads to the formation of scars (increased by collagen deposition)
