Bone
Structure of Bone
1-Periosteum
2- Bone cells
3- Bone matrix
4- Endosteum
-PERIOSTEUM
• vascular CT membrane
covering bone from outside
• Two layers
• Outer fibrous
• Inner osteogenic
-Bone Cells
Bone Cells
Osteogenic cells
(osteoprogenitor cells)
Origin
pericytes
L.M.: They are flat cells with
pale basophilic cytoplasmand
central flat nuclei
E.M.: Rich in ribsomes and rER.
Site
1-BM cavities, •
2-Endosteum & •
3-inner layer of Periosteum •
Function
Bone Growth
Healing of bone Fractures
Osteogenic cells (osteoprogenitor cells)
Bone Cells
Osteoblast cells
Origin osteogenic cells
L.M. : They are small, oval branched cells
with few cytoplasmic processes
• They have oval, eccentric, open face
nuclei.
• They have deep basophilic cytoplasm
with negative Golgi image close to the
nucleus.
E.M.: They show plenty of ribosomes, rER,
well developed Golgi apparatus and
mitochondria.
Site 1- Activated inner osteogenic layer of periosteum. •
2- Endosteum. •
3- Walls of bone marrow spaces. •
Function •
Osteoblast cells (Bone Forming Cells)
Osteoblast cells (Bone Forming Cells)
It is rich in these enzymes: •
Alkaline phosphatase enzyme: Which facilitates deposition of •
.calcium by creation of alkaline medium
Pyrophosphatase enzyme: which inhibit the action of •
pyrophosphate substances “these substances retard the process
.of calcification” i.e. indirect calcification effect
:Function •
1-They are responsible for bone formation by synthesis and secretion of bone •
matrix (Osteocalcin protein).
2- They are concerned with calcification of bone by secretion of: •
Alkaline Phosphatase and pyrophosphatase enzymes. •
Matrix vesicles, budding from the cell membrane which store Ca+. •
They change into osteocytes when they are •
. surrounded by lacunae and calcified matrix •
•
Bone Cells
Osteocyte cells
Origin Osteoblast
L.M.
- They are oval, branched cells.
• They have oval, central nuclei.
• The cytoplasm is slightly basophilic rich is
alkaline phosphatase enz.
• Osteocytes can’t divide so present singly in
each lacuna..
E.M.: - They contain rER, ribosomes, Golgi
apparatus, and many cytoplasmic
microtubules.
• The cells are present inside lacunae
between bone lamellae
• They are connected with one another by
processes passing through bone canaliculi
which connect adjacent lacunae together.
These cell processes intercommunicate •
with one another by gap junctions.
Which allow the electrolytes to pass freely •
from one cell to the other.
Bone Cells
Osteocyte cells
Sites
Function:
• They form bone matrix and
vesicles rich in enzymes which
preserve the integrity of the bone
matrix and maintain its inorganic
components.
• They are related to mobilization of
Ca+ from the bone to the blood in
times of need.
Bone Cells
Osteoclast
Origin Monocytes
Bone Cells
Osteoclast
Site
1- On the inner surface of •
bone where resorption
takes place:
2- Bone marrow spaces. •
3- Medullary cavities. •
4- Endosteum. •
Each cell lies in a shallow •
cavity called “Howships
Lacuna”.
Bone Cells
Osteoclast
Osteoclast
L.M.:
• Size: Oteoclast is large cell “2030 um”.
• Nucleus: It is multinuclated cell
“4-50” nuclei
• Shape: It is irregular in shape.
• Cytoplasm: is foamy acidophilic.
• Border: The cells have striated
or brush border facing the bone
surface.
Bone Cells
Osteoclast
E.M.:
The osteoclast shows the following 4-zones:- •
(1) Ruffled or striated zone. •
It is formed of: •
Numerous finger like processes projecting from the cell •
membrane.
Collagenous fibrils from the resorped bone matrix. •
(2) Clear Zone: •
It is a ring shaped region under the ruffled part of the cell •
membrane.
It is rich in actin filaments. •
It is called clear because it is devoid of cell organelles. •
(3) Vesicular Zone: •
It is a zone of lysosomal vesicles of variable shape and •
size.
The vesicles are rich in acid phosphatase enzyme. •
(4) Basal Zone: •
It contains nuclei (4-50) & cell organelles
•
(Golgi apparatus & mitochondria) and cell inclusions. •
Bone Cells
Osteoclast
Function:
•
1- They are concerned with bone
•
resorption during ossification causing
remodeling of the bone by the following
mechanisms.
A- Secretion of acids “lactic and
•
carbonic acids” in the tissue fluids
creates an acidic medium causing
decalcification of bone matrix.
B- Secretion of collagenase enzyme
•
which dissolves bone matrix during
ossification.
2-They remove bone debris during
•
ossification and after healing of bone
fracture.
BONE MATRIX
General charcters:
It is hard in consistency.
It is rich in blood supply.
Structure of the bone matrix:
Organic components 50%
– Collagen (typeI) It constitutes
about 90% of the organic
component.,
•
– sulphated
glycosaminoglycans,
– osteonectin glycoprotein
Which anchor cells with
bone matrix ,
– osteocalcin protein It helps
bone calcification.
Inorganic components 50%
Ca++
They are called hydroxy apitate crystals
which responsible for Bone
hardening
P+ phosphorus salts
NA+ CO3citrate
Fe+
Mg+
The hardening of the matrix is due to
1- Hydroxy apitate Crystals
2- Collagen fibrils
ENDOSTEUM
Def. vascular CT membrane that lines
inner surface of bone, BM
cavities &
Stru. Contain Osteogenic,
Osteoblast & Osteoclast
Function
1.
Provide nourishment &bl.supply
to bone
2.
Its osteogenic cells &
osteoblasts & osteoclasts are
concerned with bone
formation and resorption
during growth & healing after
fracture.
Types of Bone