2.  Introduction to skeletal system  Functions of skeletal system  Structure of the bone  Bone development Objectives

3. 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.

4. 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.

5. 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

6. 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

7. 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

8.  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 Bone structure

9.  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.

11. 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.

13. 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

15. 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

18. 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

19.  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

20. Factors regulate the bone growth  Nutrition  Calcium ions  Phosphate ions  Magnesium ions  Carbon ions  Citrate  Vitamin A& D

21. 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

22.  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