Bone & Cartilage Flashcards
Cartilage fibers
•The fibers are either solely collagenous (type II collagen) or a combination of elastic and collagenous depending on the cartilage type.
The fibrous and cellular components of cartilage are embedded in—–
matrix
Components of cartilage matrix
•Composed of a firm matrix of proteoglycans , glycosaminoglycan (GAGS) , chondroitin -4- sulphate and chondroitin-6-sulphate.
The cellular components of the cartilage
a. Chondrocytes (c), which are housed individually in a small space , lacuna
b. Chondroblasts and chondrogenic (cg) cells both of which are located in perichondrium .
Perichondrium
Cartilage is surrounded by dense irregular collagenous connective tissue membrane , the perichondrium .
Components of the perichondrium
Perichondrium consists of an outer fibrous layer (F) and an inner chondrogenic (cg) layer .
Houses chondrocytes (c)
lacuna
Chondroblasts and chondrogenic cells are located within
perichondrium
Fibrous layer of perichondrium
- Is the outer of the two layers of perichondrium.
- It consists mainly of collagen fibers and associated fibroblasts .
The inner cellular layer of perichondrium
Is the inner cellular layer of perichondrium and consists of chondroblasts and chondrogenic cells .
The layer from which the cartilage grows appositionally
Chondrogenic layer (cg)
Cells responsible for secreting the cartilage matrix
Chondroblasts (derived from cg cells)
Chondrocyte formation
cg gives rise to cbl
cbl secretes matrix and fibers
intercreated within that secretion the cells are termed chondrocyte.
1- Cartilage cells during proliferation are called
2- Cartilage cells after proliferaiton are called
1- curing proliferation- cbl
2- after proliferation- cc
chrondrogenesis
•All cartilage form from embryonic mesenchyme by the process of chrondrogenesis .
Describe each stage of cartilage development
a, b, c, d:direction of differentiation during embryonicdevelopment
a- embryonic mesenchyme
b- The first indication of cell differentiation is rounding of mesenchymal cells- Rapid multiplication (cbl during proliferation and cc after) and densly packed.
c- Production of ECM encloses the cells (cc) in their lacunae and then gradually separates Chondroblasts from one another .
d- primarily from center outwards
- Center Cells- chondrocytes (cc)
- Peripheral cells- chondroblasts (cbl)
Differentiation of superficial mesenchyme
develops perichondrium
Mechanisms of cartilage tissue enlargment (pst. differentiation)
Interstitial growth- mitosis of pre-ex cc
Appositional growth- cbl differentiation in perichondrm
(during both matrix enlargement is a factor)
Appositional growth (with time period)
involves chondroblasts differentiation from progenitor cells in the perichondrium .
seen mostly during post natal development
The slow rate for cartilage repair and/or replacement can be best explained by
Avascularity
Low metabolic rate
An example in which the replacement of cells via appositional growth is hindered due to the absence of perichondrium
•Articulating cartilage and surface
n articular cartilage , cells and matrix near the articulating surface are gradually worn away and must be replaced from within , because there is no perichondrium to add cells by appositional growth .
Hyaline Cartilage
Based on the pic, describe the major components
The perichondrium is composed of fibrous (F) and chondrogenic (CG) layers. The former is composed of mostly collagenousfi bers with a few fibroblasts, whereas the latter is more cellular, consisting of chondroblasts and chondrogenic cells (arrows).
As chondroblasts secrete matrix, they become surounded by the intercellular substance and are consequently known as chondrocytes(C).
Note that chondrocytes at the periphery of the cartilage are small and elongated, whereas those at the center are large and ovoid to round (arrowhead). Frequently, they are found in isogenous group (IG).
Elastic Cartilage
Based on the pic, describe the major components
Elastic cartilage, like hyaline cartilage, is enveloped by a perichondrium(P).
Chondrocytes (C), which are housed in lacunae (arrow), have shrunk away from the walls, giving the appearance of empty spaces. Occasional lacunae display two chondrocytes (asterisk), indicative of interstitial growth.
The matrix has a rich elastic fiber (E) component hat gives elastic cartilage its characteristic appearance as well as contributing to its elasticity.
The main fibers of hyaline cartilage
Collagen type II
Components of hyaline cartilage
- Cells ( chondrocytes) which have the characteristics of protein secreting cells (well developed rER and Golgi apparatus and a large nucleolus) and can store lipids and glycogen in the cytoplasm . A lacunar rim separates the cell from the matrix.
- Fibers , which are mainly type II Collagen fibers secreted by chondrocytes .
- ECM , also secreted by chondrocytes
Locations of elastic cartilage
•external ear , epiglottis and auditory tube .
4 characteristics of elastic cartilages
- It is avascular
- It is surrounded by perichondrium
- It consists of chondrocytes surrounded by territorial and interterritorial matrices containing type II collagen , proteoglycans and elastic fibers .
- Elastic fibers are stained with orcein stain for light microscopy .
Describe fibrocartilage
- Fibrocartilage :
- It is avascular
- It lacks perichondrium
- It consists of chondrocytes and fibroblasts surrounded by type I collagen and a less rigid extracellular matrix .
- Locations : intervertebral discs , sternoclavicular joint and pubic symphysis .
A type of cartilage without perichondrium
fibrocartilage
3 major components of bones
1- cells
2- mineralized extracellular matrix
3- high vasulature
major components of calcified matrix of bones
•The calcified matrix consists of
95%- minerals:
mostly calcium hydroxyapatite crystals and
35%- organic matter
type I collagen
sulphated glycoproteins and proteoglycans
The structural arrangement of diaphysis
In the shaft almost entire thickness of bone tissue is compact except only a small portion is spongy that faces the marrow cavity .Whereas at the ends most of the bone is spongy and only the outer shell of bone is compact .
lining of bone cavity
endosteum
Sharpys fibers
Outer surface:
•Collagen fibers are arranged in parallel to the surface of the bone except at the attachment of tendons and ligaments ,where collagen fibers extend directly into the bone tissue and are called Sharpey,s fibers .
marrow cavity of children and adults contain:
Children- Red Bone mMArrow
Blood cells of different stages in reticular fibers
Adults- Yellow Bone Marrow (fat cells)
Interstitial lamellae and lamellar bone
•Between the osteons are remnants of previous concentric lamellae called interstitial lamellae . Because of lamellar arrangement , mature bone is also called lamellar bone .
osteonal canal (Haversian)
•The osteon consists of concentric lamellae of bone matrix surrounding a central canal, called the osteonal (Haversian ) canal , which contains the blood vessels and nerves of the osteon.
Circumherrential lamellae
•Lamellar bone is also found at sites other than the osteon. Circumferential lamellae follow the entire inner and outer circumference of the shaft of a long bone , appearing much like the growth rings of a tree.
A key feature that distinguishes volkmann’s cannals (vc)
Perforating canals
•Volkmann’s canal are not surrounded by concentric lamellae, a key feature in their histological identification .
Volkmann’s canals (perforating canals)
•Perforating canals (Volkmann’s canals) are channels in the lamellar bone through which blood vessels and nerves travel from the periosteal and endosteal surfaces to reach the osteon canals .They also connect osteonal canals to one another , and run at a right angle to the long axis of osteon and of the bone .
- Part of mature bone
Mature spongy bone
simillar to compact, except tissue arrange as trabeculae/ spicules
The matrix is lamellated
Factors that distinguishes immature bones from mature
Bundle/ woven bone (non lamellar bone)
more cells/unit area
random organizaiton
has more fround substance
immaure bones in adults
- Immature bone forms more readily than the mature bone .
- Mature bone is the main type of bone in an adult whereas immature bone in adults is seen where bone is being remodeled , at the insertion of tendons and in alveolar sockets of the teeth . (orthodontic corrections)
Cell of bone tissue and their origin
- Osteoprogenitor cells (mesenchymal SC)
- Osteoblasts (MSC)
- Osteocytes (MSC)
- Bone lining cells and (MSC)
- Osteoclasts . (granulocyte-monocyte progenitor)
Locations of osteoprogenitor cells
external ( periosteal )
internal (endosteal ) surfaces of the bone and may also be found in microvasvculature of the bone . ( Harversian and Volkmann’s canals )
morphology of osteoprogenitor cells
Flat/ squamous
ovl nucleous
pale cytoplasm
rER and free ribosomes
The bone cells with PTH surface R
osteoblasts
Osteoblasts (ob)
bone – forming cells that secretes bone matrix( type I collagen) and bone matrix proteins (BMPs) which constitute the initial un mineralized bone or osteoid .
Osteoblast
morphology
communication
function
- cuboidal or polygonal shape and in a single layer lying in apposition to the forming bone .
- communicate with other osteoblasts and with osteocytes by gap junctions
Function:
- responsible for calcification of bone matrix
- PTH-R
Bone lining cells
- derived from obl
- external- periosteal cells
- internal- endosteal cells
Osteocytes
•When completely surrounded by osteoid or bone matrix , the osteoblast (ob)is referred to as osteocyte (oc).
- Bone matrix maintaining
- Ca2+homeostasis .
Bone-resorbing cells
- Osteoclasts :
- Are derived from the fusion of mononuclear hemopoietic progenitor cells.
- Newly formed osteoclasts undergo an activation process to become bone –resorbing cell .
The cells with calcitonin receptors
Octeoclasts
Osteogenesis mechanisms:
- endochondrial (cartilage precursos)
- Bones of extremities
- weight bearing axial skeleton
- im ossification
- flat bones
•Intramembranous ossification
- Bone is formed by differentiation of mesenchymal cells into osteoblasts .
- begins around the 8th week of gestation .
- Mesenchymal cells migrate and aggregate in specific areas destined to form bones . This condensation of mesenchymal cells ( ossification centers) starts the process of intramembranous ossification.
Intramembraneous ossification -after ossification centers are formed
1- inc. vasulatures
2- cytoplasmic changes that causes obl diff.
3- differentiated obl makes the matirix
- secreting type collagen
- secreting other matrix comp.
4- Newly formed bone have spicules/trabeculae
5- with matrix calcification: obl–> oc
oc have connected cytoplasms
Appositional growth (intramembraneous ossificaiton)
•With time the matrix is calcified , osteoblasts become osteocytes with their cytoplasmic processes connecting with neighboring osteocytes .This is the process of appositional growth and bony spicules increase in size and form woven bone or intramenbranous bone .
Endochondrial ossification
Periosteal bud
requires hyaline cartilage model (template- bone made within).
Cartilage does not become bone , instead a bony subperiosteal collar is formed around the midriff of the cartilaginous template
2- hypertrophy of chondrocytes (center)
3- (cells of number 2) help with calcification of the cartilage and die
4- invasion of newly formed space by the periosteal bud
Components of periosteal bud
- The hypertrophied chondrocytes assist in calcification of the cartilage and later on die .
- The newly formed spaces are invaded by the periosteal bud ( composed of blood vessels, mesenchymal cells and osteoprogenitor cells)
Osteoblasts during endochondral ossification
explan bone marrow cavity formation
- Osteoprogenitor cells differentiate into osteoblasts
- obl lay a bony matrix on the surface of calcified cartilage .
- As the sub periosteal bone collar increases in thickness and length, osteoclasts resorb the calcified cartilage – calcified bone complex, leaving an enlarged space , the future marrow cavity.
Primary ossification center
•The entire process of ossification will spread away from the primary ossification center , and eventually most of the cartilage template will be replaced by bone , forming the diaphysis of a long bone .
growth of endochondral bone
2nd trimester of pregnancu into early adulthood
•The entire process of ossification will spread away from the primary ossification center and eventually most of the cartilage template will be replaced by bone forming the diaphysis of the long bone .
Zones of epiphyseal cartilage
- As the diaphyseal marrow cavity enlarges , a distinct zonation can be recognized in the cartilage at the both ends of the cavity .
- This remaining cartilage is referred to as epiphyseal cartilage and the zones are :
- The zone of reserve cartilage ( R)
- Zone of proliferation (P)
- Zone of maturation (M)
- Zone of hypertrophy and calcification ( H)
- Zone of cartilage degeneration (CD)
- Osteogenic zone (O)
secondary ossification center & epiphyseal growth plate
Shortly after birth a secondary ossification center develops in the proximal epiphysis .As a result the cartilage remains only as the articular cartilage at the end of long bones and a transverse disc of cartilage known as epiphyseal growth plate which is responsible for maintaining the growth process
Bone remodeling unit and coupling
•The bone remodeling unit consists of 2 components :
- resorption cavity ( cutting cone )
- lamellar formation ( closing zone)
•The process of integrated bone resorption and bone replacement is known as coupling.
Harversian canal modification
Bone remodeling
- Adult bone is continuously being remodeled .
- Harversian canal systems have to be modified by osteoclastic resorption followed by osteoblastic bone formation .
- Internal remodeling:
2 units: resorption cavity and lamellar formation
