-BoneSupportive connective tissue
Mrs. Dalia Kamal Eldien
MSC in Microbiology
Lecture NO 6
Objectives
Introduction to skeletal system
Functions of skeletal system
Structure of the bone
Bone development
Introduction
Cartilage and Bone are specialized forms of
connective tissue.
They are both made up of cells embedded in an
extracellular matrix.
The nature of the matrix define the properties of
these connective tissues.
Cartilage matrix is thin, avascular, flexible and
resistant to compressive forces.
Bone matrix is highly vascularised, and its
calcified matrix makes it very strong.
Functions of bone
Support - bones make up a structural framework for
the body, and provide attachment sites for muscles.
Protection - protection of internal organs - i.e. brain,
heart and lungs,
Assisting movement.
Storage of mineral - the bone is a store for
calcium and phosphorus
Blood cell production - takes place in the bone
marrow.
Bone structure
 Bone made up of Cells and Extracellular matrix:
 Cells - contribute only about 2% from the bone
mass, which in bone are:-
1- Osteoblasts (osteo = bone, blast= immature cell)
 immature bone cells, lining the surface of bone
 produce collagen and the organic matrix of bone
(osteoid), which becomes calcified soon after it has been
deposited.
 As they become trapped in the organic matrix, they
become osteocytes.
 Osteoblast are involve in making new bone by process
refer as osteogenisis
Bone structure
2- Osteocytes
 Are the mature bone cells maintain bone tissue.
 Osteocytes sit in the calcified matrix, in small spaces
called lacunae (lacuna - singular).
 Long processes from the osteocyte lie in small
channels called canaliculi (small canals).
 These are channels for the transport for nutrients and
waste.
 The osteocyte processes contact other ostocytes,
forming gap junctions, so that they can communicate
with each other.
Bone structure
3-Osteoprogenitor cells
 Are the 'stem' cells of bone, and are the source of
new osteoblasts
4-Osteoclasts
 Are, large multinucleated cells, with a 'ruffled border‘
 produce acid which dissolve the bone therapy to
release the calcium& phosphate ions in to the blood
by process refer as osteolysis
 Are not derived from osteoprogenitor cells.
 They are derived from blood monocytes
Bone structure
Extracellular matrix
 Which is made up of an organic matrix (30%)
containing proteoglycans (but less than cartilage),
glycosaminoglycans, glycoproteins, osteonectin and
osteocalcin .
 There are collagen fibers (mostly type I (90%) help
the bone to resist tensile stresses
 Almost 70% of bone is made up of bone mineral
(Calcium& Phosphate)called hydroxyapatite.
 The collagen fiber& hydroxyapatite make the bone
tissue extremely stronger
 Before the extracellular matrix is calcified, the tissue is
called osteoid (bone-like) tissue.
 When the concentrations of calcium and phosphate
ions rise high enough, they are deposited into the
extracellular matrix, and the bone calcifies.
Types of bone
There are two types of mature bone can be distinguished
macroscopically:
1. Compact (lamellar bone)
 Is composed of cylindrical structures called osteons
(it was the basic unit of bone structure, consist of
central canal, canaliculi, osteocyte, lacunae&
lamellae)
 Found in the shafts of long bones (in the diaphysis).
 This makes up 80% of all bone .
 They are dense& solid .
 Osteoblasts deposit the matrix in the form of thin sheets
which are called lamellae.
Types of bone
2. Spongy (cancellous or Trabecular bone)
 which is found at the ends of long bones (in the
epiphysis).
 This makes up 20% of all bone.
 This type of bone contain red bone marrow .
 The spongy bone create the light weight nature of
the bone
The bone are consist of two layers
 A ‘Periosteum' is found on the outside of bone. This
is a dense fibrous layer, where muscles insert. It
contains bone forming cells. It is isolate and protect
bone from surrounding tissue. Actively participate in
bone growth& repair
 The Endosteum is the tissue that lines the inner
surfaces of bones. Consist of osteoprogenitor cells
Growth of bone
Formation of Bone in an Embryo
cartilage formation and ossification occurs during the
sixth week of embryonic development in two patterns
• Intramembranous ossification
• Flat bones of the skull and mandible are
formed in this way
• “Soft spots” that help the fetal skull pass
through the birth canal later become
ossified forming the skull
• Endochondral ossification
• The replacement of cartilage by bone
• Most bones of the body are formed in this
way including long bones
 Unlike cartilage, bone has a very good blood
supply. The central cavity contains blood vessels
and is a storage for bone marrow.
 Osteogenesis: bone formation
 Calcification: deposition of calcium ions in to the
bone tissue
Factors regulate the bone growth
 Nutrition
 Calcium ions
 Phosphate ions
 Magnesium ions
 Carbon ions
 Citrate
 Vitamin A& D
Factors regulate the bone growth
 Parathyroid gland release the parathyroid hormone
 Stimulate the osteoclasts
 Stimulate the osteoblasts
 Increase the calcium ions absorption from the
small intestine
 Thyroid gland release the calcitonin
 Inhibit the osteoclasts
 Remove the calcium ions from the blood and add it
to bone
 Thyroid gland release the Thyroxine (T4)
 Maintain the normal activity of the epiphyseal
cartilage(cartilage near the diaphysis convert to bone)
 The pituitary gland release growth hormone
(somatotropin)
 Maintain the normal activity of the epiphyseal cartilage