Mineralized Tissues Flashcards
Background on connective tissue
Cells + extracellular matrix
Matrix: can be gel-like, hard, fluid; usually protein
-supports and binds cells
-exchange medium
-“rigid” connective tissue with
A. Glycosaminoglycans (usually chondroitin sulfate), GAGs
B. proteoglycans (core protein with attached GAG chain)
Mineralization
Deposition of minerals (Ca and P salts) in connective tissue matrix
Advantages of mineralization
Mechanical strength/support
Storage for later use
If mineralized, cells in matrix may become isolated from blood…
=entombment
O2, CO2, nutrients
Mineralized examples
Bone, cartilage, dentin, enamel (or enameloid)
Common themes regarding mineralized tissue
A. Collagen is present
Collagen bundles form network for mineral deposition in connective tissue
B. hydroxyapatite is abundant in dentin and bone
Mineralization processes
- Calcification
- Dentin formation
- Ossification
Calcification (calcified cartilage)
major cartilage components:
- fibroblast: collagen matrix
- chondroblast: sulfated GAGs and proteoglycans in matrix
chondroblasts entombed in lacunae = chondrocytes (cartilage cell) with reduced mitotic ability
diffusion supplies lacunar cells; poor vascular supply
repair of bone quicker than cartilage
compared to bone, cartilage…
- has a lower metabolic rate; avascular
- has different cellular and extracellular components (thus different structural properties)
- cells are chondrocytes suspended in semi-rigid matrix
- matrix with collagen and/or “fibrous proteins” (collagen absent in some lampreys and hagfishes, present in others)
- matrix is rich in polysaccharides
hyaline cartilage
least differentiated; translucent; often converted to bone
Ex, “growth plate” in limb bones, tracheal rings, articular surfaces of joints, larynx, nose
fibrocartilage
intervertebral discs and pelvic girdle symphyses
elastic cartilage
pinna, epiglottis
calcified cartilage
Ca salts released into/form in matrix; usually hyaline or elastic; often appears bone-like
calcification
=calcium salts entomb chondrocytes; lacunar cell death
Ex:
- jaws of chondrichthyes
- endochondral bone formation before replacement by osseous tissue
- atypical - joint damage in osteoarthritis patients (calcium pyrophosphate dihydrate and calcium phosphate)
Dentin Formation
mineralization: cell vitality retained
forms only in dermis, usually near epidermal border
odontoblasts reside near dermal blood vessels
cytoplasmic extensions of ondontoblasts deposit dentin - odontoblastic process
- 30% organic (collagen and GAGs)
- 70% inorganic (hydroxyapatite)
- extensions project away from blood vessel
odontoblast “retreat” toward blood vessel; cell extenstions become embedded in dentin
odontoblastic processes become surrounded by dentin matrix
microscopic “tunnels” through mineralized tissue - canaliculi or dentin tubules
odontoblasts aggregate; dental pulp
dentin is usually covered by epidermal enameloid (enamel, ganoin)
enameloid produced by ameloblasts in epidermis
enameloid applied to surface of dentin teeth, fish scales
Ossification
not restricted to dermis
bone: always with collagen fiber matrix
spaces between fibers filled with hydroxyapatite
crystals bound to collagen by cementing substance (water and mucopolysaccharides)
hydroxyapatite hardens, cells extensions surrounded
microscopic tunnels though mineralized tissue = canaliculi
clusters of 2-4 osteoblasts reside in lacunae with interstitial fluid
cells retain direct/indirect access to vascular supply via canaliculi
cementing substance similar to dentin, but…
- cells (osteoblasts) with cytoplasmic extensions in several directions
- osteoblasts are perivascular regarding vascular supply
- extensions contact other osteoblasts
- usually no cell retreat as hydroxyapatite produced
bone: similar composition as dentin
30% organic (collagen and GAGs)
70% inorganic (hydroxyapatite)
enamel
96% inorganic hydroxyapatite; acellular
ameloblasts
enamelin and amelogenin, epidermis
types of bone cells
osteoprogenitor
osteoblasts
osteocytes
osteoclasts
osteoprogenitor cells
unspecialized; mesodermal mesenchyme origin; mitotic
osteoblasts
bone-forming cells; osteogenesis; not mitotic
osteocytes
“mature” osteoblast; maintenance; not mitotic
osteoclasts
derived from monocytes
all bone ultimately derived from…
mesodermal mesenchyme
Types of Bone
Presence/Absence of Cells:
- cellular bone
- acellular bone - common in fishes
Appearance:
- compact
- cancellous - spongy or trabecular bone (trabecular spaces and trabeculae)
Orientation of collagen:
- lamellar bone - regular arrangement of collagen and bone cells (think osteon)
- non-lamellar bone (spongy bone, dermal bone)
Formation:
- membrane bone
- endochondral bone
Haversian bone (osteonic bone)
=lamellar bone
mineralized collagen bundles surrounding haversian/osteonic canal; lamellae
Each canal: arteriole, venule, lymph vessel, neurons
Canal and surrounding lamellae with lacunae = osteon
blood vessels in osteon connected to blood vessels outside bone
Volkmann’s canal
perforating canal - nutrient foramen
spongy bone (=cancellous bone)
porous, trabeculae
trabeculae = beams/bars, architectural trusses
trabeculae with irregular lamellae, no organized osteonic systems
red marrow
red marrow in spaces between trabeculae = hemopoietic/hemapoietic tissue
compare yellow marrow (in medullary cavity)
abundant in flat bones (roofing bones of skull, ribs, scapulae)
membrane bone
no cartilage precursor
mesodermal mesenchyme cells arrange in layers (sheet-like “membranes”; membranous blastema)
these cells become osteoblasts
types of membrane bone
- dermal bone
- perichondral/periosteal bone
- heterotopic bones
heterotopic bones
usually respond to mechanical stress
- sesamoid bones
- os cordis (fibrous connective tissue between A&V, interventricular septum)
- baculum (in fibrous connective tissue above urethra; bats, rodents, dogs, some primates, otter, walrus, raccoon)
- rostral bone
