Cartilage & Bone Flashcards
Cartilage and bone are types of
Connective tissue —> they consist of cells within a matrix
Cartilage Matrix (4)
-firm gel
-composed of proteoglycans (thick viscous protein) and collagen
-solid, yet flexible
-lacks nerves/blood supply —> poor healing properties
Chondroblasts are
Immature cartilage cells that lay down matrix
Chondrocytes are
Mature cartilage cells
Lacunae are
Spaces within the cartilage matrix that house Chondrocytes
Chondrocytes are isolated in small chambers called
Lacunae
The Cartilage matrix is also called
Ground substance
Perichondrium is (3)
-fibrous connective tissue
-Outer Layer = irregular, dense connective tissue
-Inner Cellular Layer
Cartilage forms the ___ which is then replaced by ___, with the exception of ___
Fetal skeleton; bone; joints
Cartilage is found at
Articular surfaces
Cartilage is surrounded by a tough, dense fibrous capsule called the
Perichondrium
Two layers of the Perichondrium are
-outer layer of irregular dense connective tissue
-inner cellular layer of chondroblasts involved in growth
Cartilage grows by two mechanisms
-interstitial growth (growth from within)
-appositional growth (growth from outside)
Interstitial Growth (3)
-Chondrocytes (immature cartilage cells) divide creating isogenous groups of daughter cells
-daughter cells produce matrix and push cells apart (ie. cartilage gets bigger and longer)
-growth from within
Appositional Growth (3)
-growth by adding to the outer surface of existing cartilage
-chondroblasts divide in the inner layer of the Perichondrium, producing a matrix
-cells then differentiate into Chondrocytes (mature cartilage cells)
Three types of cartilage
-Hyaline
-Fibrocartilage
-Elastic Cartilage
Most common type of cartilage is
Hyaline
Hyaline Cartilage (6)
-most common type of cartilage
-smooth, glassy, and shiny looking
-dense Perichondrium (except at joints)
-matrix contains closely packaged collagen fibres
-in the fetus, forms the skeletal template
-in adults, is the sternal end of ribs, articular surfaces of joints, nasal septum, larynx, and tracheal rings
Fibrocartilage (5)
-intermediate between dense connective tissue and cartilage
-Chondrocytes (mature cartilage cells) are aligned in rows, between layers of interwoven collagen fibres
-resists compression
-absorbs shock
-found in intervertebral discs (annulus fibrosus ie. outside layer) and menisci of stifle joints
Elastic cartilage (4)
-contains numerous branching elastic fibres within the matrix
-matrix also contains collagen
-resilient and flexible
-found in the pinna of the ear, auditory (eustachian) tube, epiglottis, and larynx
Which type of cartilage is found at the sternal end of the ribs, articular surfaces of joints, nasal septum, larynx, and tracheal rings?
Hyaline Cartilage
Which type of cartilage has elastic fibres
Elastic Cartilage
Which type of cartilage forms the skeletal template in the fetus
Hyaline
Which type of cartilage is interwoven collagen fibres?
Fibrocartilage
Which type of cartilage is found in the menisci of the stifle joint and intervertebral discs?
Fibrocartilage
Which type of cartilage is closely packed collagen fibres?
Hyaline
Which type of cartilage is found in the pinna of the ear, auditory (eustachian) tube, epiglottis, and larynx?
Elastic Cartilage
Two types of bone
-Compact
-Cancellous/Spongy
Bone matrix (4)
-calcified (CaPO4 and CaCO3)
-hard
-storage for calcium
-contains collagen fibres (relatively flexible, tolerates tension/compression, light)
Bone (3)
-makes up the bulk of the skeleton
-strong, relatively flexible, resistant to shattering
-used for physical support and protection
Compact bone (3)
-located on the surface (outside) of bones
-sturdy, protective layer
-thickest where stresses are the greatest
The ratio of compact:cancellous bone
Varies with the shape of bone (ie. long vs flat bones)
Cancellous bone (2)
-located in the interior of bones
-contain trabeculae (open network of bony plates)
Outer layer of bone is ___ and the inner layer of bone is ___
Compact; Cancellous/Spongy
Trabeculae are
Open networks of bony plates in cancellous bone
Examples of long bones include (3)
-forelimb
-hindlimb
-digits
Long bones consist of (3)
-diaphysis (holly shaft containing marrow)
-epiphyses (ends, may be surrounded by cartilage)
-metaphyses (narrow region between the diaphysis and epiphyses)
Long bones contain both
Cancellous and Compact Bone
Diaphysis (2)
-outer layer of compact bone called the Cortex
-central space called the Medullary Cavity that contains marrow
Epiphyses (4)
-thin cortex of compact bone
-central area of cancellous bone
-ends of long bone
-may be surrounded by cartilage
The narrow region between the diaphysis and epiphyses is the
Metaphyses
The shaft of long bones is called the
Diaphysis
The medullary cavity contains
Bone marrow
Flat bones include (4)
-skull
-ribs
-sternum
-scapulae
Flat bones lack a ___
Medullary cavity
The skull is formed from
Mesenchyme
The ribs, sternum, and scapulae are formed via
Endochondrial ossification
In flat bones, marrow is
Dispersed within cancellous bone —> there is no medullary cavity
Structure of flat bones
Centre of cancellous bone sandwiched between two thick layers (tables) of compact bone
Periosteum (4)
-covers the outer layer of compact bone
-not found at articular surfaces
-becomes interwoven with tendons
-has an outer fibrous layer and an inner cellular layer
The inner cellular layer of the periosteum (2)
-functions in bone growth and repair
-has osteogenic properties
Two layers of the periosteum
-outer fibrous layer
-inner cellular layer
Endosteum (4)
-thin cellular layer
-lines medullary cavity and trabeculae of cancellous bone
-has osteogenic properties
-functions in bone growth and repair
Osteogenic Properties means
Can divide and produce Matrix
Four types of bone cells
-osteoprogenitor cells
-osteoblasts
-osteocytes
-osteoclasts
Osteoprogenitor Cells (5)
-derived from Mesenchymal stem cells
-divide to produce daughter cells that differentiate into Osteoblasts
-pale staining nuclei and cytoplasm (difficult to distinguish)
-located in the inner celllular layer of periosteum and endosteum
-important in fracture repair
Osteoblasts (5)
-immature bone cells
-reduce the Matric
-form an epithelial layer in areas of active growth
-prominent nucleolus
-basophilic cytoplasm
Mature bone cells are called
Osteocytes
Immature bone cells are called
Osteoblasts
Osteocytes (7)
-mature bone cells developed from osteoblasts
-most abundant cell type in bone
-cannot divide
-occupy Lacunae in formed bone
-contact one another via Canaliculi (tunnels running to various lacunae)
-maintain protein and mineral content of the Matrix
-can be de-differentiated into osteoblasts and osteoprogenitor cells to help repair damaged bone (not efficient)
Canaliculi are (2)
-cytoplasmic extensions through narrow tunnels that run to various lacunae
-allow osteocytes to contact one another
Which bone cell cannot divide
Osteocytes
Osteoclasts (4)
-syncytia (fusion) of many cells with over 50 nuclei
-involved in bone resorption, Ca2+ and PO4 regulation, and bone remodelling
-derived from monocytes (circulating macrophages)
-found in areas of restored bone called Howship’s Lacunae at the junction of bone and endosteum
Collagenase is
An enzyme that breaks down collagen
Howship’s Lacunae
Areas of resorbed bone containing osteoclasts, found at the junction of bone and endosteum
The bony matrix is laid down in
Lamellae
Lamellae surround
Uniformly spaced osteocytes in lacunae
Radiating from lacunae are
Canaliculi that ramify throughout lamellae
In compact bone, lamellae are laid down in 3 forms
-Haversian Systems (Osteons)
-Interstitial Lamellae
-Circumferential Lamellae
Haversian Systems (Osteons) (4)
-osteocytes arranged in concentric lamellae around a central Haversian Canal
-Haversian canals contain one or more blood vessels
-aligned parallel to long axis of bone
-Volkmann’s Canals at a right angle to Haversian canals
Interstitial Lamellae (2)
-between Haversian Systems
-non-concentric lamellae (ie. they fill in the spaces)
Circumferential Lamellae (2)
-encircle bone
-located beneath the periosteum and endosteum
In Cancellous/Spongy Bone (3)
-lamellae are not arranged in Haversian Systems
-matrix from trabeculae
-nutrients reach osteocytes via diffusion along Canaliculi that open onto the surface of trabeculae
Bones form via two processes:
-Cartilage Model (endochondrial ossification)
-directly from Mesenchyme (intramembranous ossification)
Immature Trabeculae are called
Spicules
Formation of bone via Intramembranous Ossification (7)
- Embryonic Mesenchymal cells cluster and secrete Matrix
- Mesenchymal cells differentiate into Osteoblasts at the ossification centre
- Developing bone extends from ossification centre as spicules where osteoblasts become trapped and transform into osteocytes
- Blood vessels grow into developing bone
- Matrix is calcified
- Initially formed as cancellous/spongy bone
- Remodelled into compact bone
In Intramembranous Ossification, there is no
Cartilage precursor
Most bones will form via
Endochondral Ossification (Cartilage Model)
Which bones form via Intramembranous Ossification?
-flat bones of skull
-mandible
-clavicle
Which bone cells secrete Matrix
Osteoblasts
Bone Formation via Endochondral Ossification (6)
- In the Diaphysis, Chondrocytes hypertrophy and die as the surrounding matrix calcifies (Primary Centre of Ossification)
- Cells of Perichondrium differentiate into Osteoblasts and lay a thin bony collar around the surface of the cartilaginous (hyaline) diaphysis
- Blood vessels grow into the Perichondrium and invade spaces left by the dying Chondrocytes
- Fibroblasts migrate into areas left by dying Chondrocytes
- Fibroblasts differentiate into Osteoblasts and lay down Cancellous Bone
- Secondary Centres of Ossification in the Epiphyses form cancellous bone, the cartilage remains on articular surfaces and at the level of the metaphyses (ie. ephyphyseal plates/growth plates)
5 zones of Endochondral ossification
Zone 1: resting cartilage
Zone 2: proliferating cartilage
Zone 3: hypertrophic cartilage
Zone 4: calcified cartilage
Zone 5: ossification
Continued growth in length of long bones occurs at the
Epiphyseal Plate
The epiphyseal plate remains
A constant length until growth has ceased (ie. maturity)
Continued growth in long bones (5)
- Chrondrocytes multiply at Epiphyseal Plate
- Chondrocytes mature and hypertrophy at diaphyseal end and lay down calcium
- Chondrocytes die; capillaries and Osteoprogenitor cells fill the remaining spaces and lay down bony Matrix on the calcified cartilage spicules
- Bone at diaphyseal end is eroded by Osteoclasts, enlarging the marrow cavity
- Chondrocyte proliferation equals rate of osteoclast remodelling
Spicules will mature into
Trabeculae
Growth in long bone diameter occurs via
Appositional Growth (adding to the outside)
The medullary cavity will ___ as bone increases in diameter due to _____
Enlarge; osteoclasts removing bone from inside the bony collar to expand the medullary cavity
