Bone Chapter 4 PDF

BONE DR/ GhaDa MOhaMED  Chapter 4: Bone ❖ Definition: It is a highly vascular & hard type of connective tissue. It is the hardest type of C.T. as it has Calcified matrix. Since it is a type of connective tissue, it consists of cells, fibe...

BONE DR/ GhaDa MOhaMED  Chapter 4: Bone ❖ Definition: It is a highly vascular & hard type of connective tissue. It is the hardest type of C.T. as it has Calcified matrix. Since it is a type of connective tissue, it consists of cells, fibers & matrix. ❖ General structure of bone: The main components of bone are: a- Matrix & fibers. B- Bone Cells c- Bone covering Bone matrix &fibres - Bone matrix is formed of two main parts: 1- Organic Part (35%): It is mainly formed of type I collagen fibers which are arranged as thick bundles & ground substance 2- Inorganic Part (65%): It is mainly formed of calcium salts in the form of calcium phosphate & carbonate. They are present on the surface of collagen bundles & also within the ground substance & cause hardness of bone. Bone Cells Osteogenic cells Osteoblast Osteocyte Osteoclast [Bone forming] Bone maintaining Bone Destroying Origin UMC & pericytes Osteogenic cell Osteoblasts Blood monocytes Site Present in the inner Present immediately Singly in bony On the surfaces of layer of periosteum under the periosteum lacunae bone near the bone & endosteum Also present under the Lacunae connect marrow endosteum. by canaliculi Howship's lacuna. Cannot Divide Cannot Divide L.M. Flat cell Oval cells with minute Oval cells with Large irregular Flat nucleus few processes fine processes. cells having Pale basophilic Eccentric nuclei. Oval central N brush border cytoplasm Cytoplasm is darkly Cytoplasm is multinucleated basophilic lightly basophilic cells (6-12), with Rich in alkaline Alkaline foamy phosphatase enzyme. phosphatas Acidophilic. E.M. rER,Golgi& Mit Rich in r ER, Golgi Less r ER, Golgi Microvilli ribosomes apparatus & Mit apparatus Lysosomes Functions They divide & 1-They are bone forming 1-Bone I-Bone Resorption in differentiate to cells. maintaining cells two steps: osteoblasts 2-Secrete the organic part 2-Form organic 1- Remove calcium o They are of the matrix &inorganic part [decalcification] numerous in 3-Alkaline phosphatase of the matrix. 2Secrete lysosomal young age enzyme deposits proteolytic enzymes &fracture. calcium remove organic part o Change to 4-They change into N.B. Lacuna II-Bone remodeling chondroblasts in imprisoned cells called contains Only one N.B. Osteoclasts area of poor osteocytes. osteocyte unlike not phagocytic cell vasculature chondrocytes 1  Bone covering &fibres 1- Periosteum: Definition: A connective tissue which covers the outer surface of bone. Structure: It consists of a- Outer fibrous layer: It is formed of a layer of dense collagen fibers, fibroblasts & blood capillaries. b- Inner osteogenic layer: It is formed of osteogenic cells. This layer is very thick in case of growth & fracture as osteogenic cells multiply & differentiate to osteoblasts. Functions: 1) Protection of bone. 2) Nutrition for bone. 3) Bone growth as osteogenic cells differentiate to osteoblast which form bone matrix & change to osteocytes (appositional growth). 2- Endosteum: Definition: It is a delicate layer of connective tissue that contains a single layer of osteogenic cells. Functions: 1- Protection of bone 2- Bone growth by adding from inside Methodes of bone preparation A) Decalcification method: - Calcium is removed by treating the bone with mineral acid as nitric acid 10%. - Bone becomes soft & sections can be cut and stained. - Decalcified bone sections demonstrate the bone cells and soft tissues. B) Grinding method: - Bone is left to dry in air. - Small pieces of the bone are cut by a saw. - Ground bone sections are unstained sections which only show the bone lamellae, the lacunae, canaliculi (no cells) & Volkmann's canals. N.B. Grinding method cannot be used for spongy bone sections. Classification of bone 1- Compact bone: It has regular bone lamellae [Haversian system]. 2- Spongy bone: It is formed of irregularly arranged bone trabeculae & multiple bone marrow cavities. General component of compact bone ❖ Sites: It forms the shaft of long bones & also presents as a covering over spongy bone. ❖ It is formed of: 1- Periosteum: It covers the outer surface of bone. 2- External Circumferential Lamellae: They are found under the periosteum & parallel to the surface of bone. 3- Haversian System (OSTEON): It is the structural units of compact bone. 2  It is a cylindrical structure which is longitudinally arranged parallel to longitudinal axis of bone shaft It is formed of a central canal (Haversian canal) that contains b.vs. & nerves embedded in loose C.T. surrounded by 5-20 of concentrically arranged circular bony lamellae & osteocytes within lacunae embedded in between them. Compact bone has transverse or oblique canals that connect the Haversian canals together & with periosteum or bone marrow cavity, they are called Volkmann's canals 4- Interstitial Lamellae: They are irregularly arranged bony lamellae & in between Haversian systems. 5- Internal Circumferential Lamellae: These are bone lamellae parallel to the inner circumference of bone & they surround the bone marrow cavity. 6- Endosteum: It lines the bone marrow cavity. General component of spongy bone Sites: Spongy bone is present in the center of flat bones, short bones, irregular bones as well as epiphysis of long bones. Structure: It is formed of irregular branching & anastomosing bony trabeculae enclosing between them irregular bone marrow cavities. Each trabeculum is formed of irregularly arranged bony lamellae & osteocytes, No Haversian system. Bone surface is covered by periosteum & bone marrow cavities are lined by endosteum. 3