Charles University in Prague, First Faculty of Medicine
Types of bone tissue, structure and
function. Bone histogenesis.
Dentin and cementum.
Doc. MUDr. Marie Jirkovská,CSc
Institute of Histology and Embryology
Subject: GHGE
Code: B82241
Bone
hard connective tissue composed of cells and ECM, supports and protects
the body, serves as storage site for calcium and phosphate (controlled by
parathyroid hormone and calcitonin)
Cells: osteoprogenitor cells, osteoblasts, osteocytes, osteoclasts
ECM:
organic component 35%
collagen fibrils (type I collagen), minor collagens (III, V, XI, XIII)
hyaluronan, proteoglycans, GAGs (chondroitin sulfate, keratan sulfate)
multiadhesive glycoproteins (osteonectin, sialoproteins I and II,
osteopontin) - responsible for the attachment of cells and fibrils to the mineralized
ground (amorphous) substance
osteocalcin - captures calcium from the circulation and stimulates osteoclasts
growth factors and cytokines – e.g. bone morphogenic proteins
(BMPs - they induce the differentiation of mesenchymal cells to osteoblasts – used
also clinically)
inorganic component 65% (hydroxyapatite)
Bone cells
Osteoprogenitor cells (osteoblast precursor cells) - derived
from mesenchymal cells, have a potential to differentiate into osteoblasts.
They reside on external and internal bone surface (in the innermost layer of
periosteum and endosteum) and in bone vasculature.
Cells associated with bone
Bone cells
Osteoblasts
differentiated bone-forming cells, able to
divide, display basophilic cytoplasm as
they secrete bone matrix (osteoid) =
collagen I, proteoglycans, multiadhesive
glykoproteins, calcium - binding proteins,
alkaline phosphatase (strong ALP
reaction on the surface membrane),
matrix vesicles (calcification)
Osteocytes
→ osteoblasts surrounded by bone matrix,
they react on tensile forces and are responsible
for the maintaining of the adjacent bone matrix
(synthesis and degradation)
cytoplasmic processes in canaliculi ossium
lacuna
osteoblast
A.L.Kierszenbaum:
Histology and Cell
Biology
Communication by gap junction
between osteoblasts and osteocytes
projections located in canaliculi ossium
Bone cells
Osteoclasts
Histology
L.P.Gartner, J.L.Hiatt: Color Textbok of
large (50-100 µm) multinucleated (up to 10 nuclei) cells resulting from the fusion of
granulocyte/macrophage precursor cells, responsible for bone resorption. The active
osteoclast exhibits:
a) rufflet border (deep plasma membrane infoldings, exocytosis of hydrolytic enzymes
and protons, endocytosis of degradation products and bone debris),
b) clear zone (demarcates and seals bone area being
osteoclast – markedly
resorbed - actin filaments), c) basolateral region
acidophilic cytoplasm
(exocytosis of digested material)
resorption bay
(Howship´s lacuna)
Structure of bones
immature bone (woven, bundle bone) – characterized by interlacing arrangement
of collagen fibrils; in developing fetus; in adults in alveolar sockets and tuberosities
mature bone (lamellar bone) - compact and spongy type (long axes of
osteocytes parallel to bone lamella, collagen fibrils arranged parallel in the lamella)
Compact bone
L.C.Junqueira et al.: Basic Histology
L.C.Junqueira et al.: Basic Histology
Lamellar compact bone
Haversian canals
Interstitial lamellae
Circumferential lamellae
Bone remodeling
longitudinal section
cross sections
Lüllmann-Rauch:Histologie
Lamellar spongy bone
arranged as trabeculae (spicules)
bone marrow
Bone histogenesis
Intramembranous ossification - flat bones of the skull and face, mandible,
Endochondral
clavicle
ossification - vertebrae, bones of the extremities
Intramembranous ossification - mesenchyme cells aggregate in areas
destined for the formation of the bone, then differentiate into osteoprogenitor cells
and then into osteoblasts (production of osteoid)
appositionally growing bone spicules
osteocyte
osteoclast
osteoblasts
Endochondral ossification begins
in second trimester of fetal life
begins with aggregation of mesenchymal cells
which differentiate into chondroblasts
(-> hyaline cartilage model surrounded by
perichondrium)
1) bone collar around the model
2) chondrocytes in the midregion become
hypertrophic, the surrounding matrix calcifies
Endochondral ossification
3) blindly ending blood vessels (osteogenic
buds) grow through the bony collar into the
cartilage (chondroclasts), mesenchymal cells
migrate along the blood vessels and
differentiate into osteoprogenitor cells
Endochondral ossification
4) osteoprogenitor cells come to apposition to
the remaining cartilage spicules and produce
osteoid (osteoblasts);
primary ossification
centre is formed
Endochondral ossification
4) osteoprogenitor cells come to apposition to
the remaining cartilage spicules and produce
osteoid (osteoblasts);
Growth of endochondral bone
stimulated with GH (osteoprogenitor cells), IGF I (chondrocytes)
Bone repair after injury (fracture)
periosteum periosteal proliferation bone
callus
hyaline cartilage
repaired bone
Matrix vesicles and mineralization: mineralization is a cell regulated event, it occurs in ECM
of bone, cartilage, cementum, dentin (collagen fibrils and ground substance). It involves the secretion
of matrix vesicles (membrane limited, 50-250 nm) into the matrix. High local concentration of Ca+2 in
the osteoblast (osteocalcin) stimulates the production of ALP which enhances the local concentration
of phospate ions. Exocytosis of matrix vesicles (ALP, pyrophosphatase, Ca+2) more enhances the local
concentration of phospate ions → crystallization of calcium phosphate which initiate formation and
deposition of hydroxyapatite crystals.
Dentin and cementum
Tooth:
Enamel
Dentin
Dental pulp
Cementum
M.H.Ross,W. Pawlina: Histology
dentin
predentin
A. Stevens, J.S. Lowe: Histology
Dentin
Odontoblasts + ECM (collagen
fibrils, proteoglycans).
Osteocalcin, dentine
phosphoprotein and dentine
sialoprotein are involved in
mineralization, 70% of EMC
comprises hydroxyapatite.
B.K.B.Berkovitz et al. Oral
Anatomy, Histology and
Embryology
B.K.B.Berkovitz et al. Oral
Anatomy, Histology and
Embryology
Cementum
its structure is similar to the woven bone (cca 65% of inorganic
component), cover of the neck and root of the tooth
acellular
cementum
P
C To
Dent
cellular
cementum
P-periodontal ligament; C-cementun; To-granular layer of Tomes at the contact
of dentin and cementum, Dent-dentin