L5 - BONES.pdf

ITM 101 | HISTOLOGY LESSON # 4 - BONES 1st YEAR A.Y. 2023-2024 | SEPTEMBER 7, 2023 DR. FERDAUZIA E. BASTERO THE BONE -is a special type of connective tissue with a hard matrix. -it is also rich in blood supply. TWO TYPES OF BONE 1. Com...

ITM 101 | HISTOLOGY LESSON # 4 - BONES 1st YEAR A.Y. 2023-2024 | SEPTEMBER 7, 2023 DR. FERDAUZIA E. BASTERO THE BONE -is a special type of connective tissue with a hard matrix. -it is also rich in blood supply. TWO TYPES OF BONE 1. Compact or Cortical Bone (substantia compacta) -makes up approximately 80% of total skeletal tissue mass. -solid continuous mass made up of osteons. 2. Spongy or Cancellous Bone (substantia spongiosa) -3D lattice of branching bony spicules (trabeculae) occupied by bone marrow. Bone Functions Provide support Protect the vital organs Storage of calcium PARTS OF LONG BONE Figure 1. Parts of long bone TEST YOURSELF !! Diaphysis (shaft) - consists of thick walled hollow cylinder of compact bone with central marrow cavity (medullary cavity) occupied by the bone marrow Epiphysis - ends of long bones arising from separate ossification centers and separated from the diaphysis by the cartilaginous epiphyseal plates Epiphyseal Plate - a cartilaginous plate separates the Epiphysis and Diaphysis. Metaphysis - From the epiphyseal plate there is a transition growth bone which we call the metaphysis wherein the growth of the bone occurs. Periosteum – the specialized connect tissue that covers most of the bone is also the site which has osteogenic properties – or form new bones especially during repairs of fractures. Note: some bones do not have a periosteum covering (sesamoid bones) INTRODUCTION TO MEDICINE 101 | HISTOLOGY LESSON # 4 : BONES AYURA 2027 1 ITM 101 | HISTOLOGY LESSON # 4 - BONES 1st YEAR A.Y. 2023-2024 | SEPTEMBER 7, 2023 DR. FERDAUZIA E. BASTERO Endosteum - lines the marrow cavity inside of the diaphysis which also has the ability to form new Volkman’s canal - connects haversian canals from bones. one another. They traverse the bone in a direction perpendicular or oblique to the osseous lamellae. BONE TISSUE BONE CELLS Bone tissue is made up of four different types of bone cells; 1. osteoprogenitor cells 2. osteoblasts 3. osteocytes 4. osteoclasts Together these cells comprise the compact and spongy bone layers and work together to maintain the mineral composition and structure of the bones. Figure 2. Bone tissue under microscope Bone Matrix - The bone is surrounded by the bone matrix which as an interstitial substance 3-7 micrometers thick, most of the constituents of the bone are floating in this bone matrix. Lacunae – these are uniformly spread throughout the interstitial space they contain the bone cell or osteocytes Canaliculi – radiating structure from the lacunae and comes into contact with nearby lacunae. Connects one lacunae from another lacunae. Allows for the exchange of nutrients and waste products between lacunae. OSTEOPROGENITOR CELLS Haversian Systems (osteons) – basic unit of bone. Appear as concentric rings made up of 4-20 lamellae Osteoprogenitor cells, also known as osteogenic cells, are stem cells in the bone Interstitial systems - angular pieces of lamellar that play a prodigal role in bone repair and bones between haversian canals growth. Outer and Inner laellae - several lamellae that These cells originate from infant mesenchymal extend uninterrupted around much of the cells and turn into spindle cells at the surface circumference of the shaft of matured bones and remain in place throughout postnatal life. Haversian canals - vascular longitudinal channels in ➔ Osteoprogenitor cells are most active the centers of osteon. They are 22-110 um in diameter during the growth of bones but are and contain one or two small blood vessels, mostly reactivated in adult life in the repair of capillaries and postcapillary venules. bone fractures and other forms of injury. INTRODUCTION TO MEDICINE 101 | HISTOLOGY LESSON # 4 : BONES AYURA 2027 2 ITM 101 | HISTOLOGY LESSON # 4 - BONES 1st YEAR A.Y. 2023-2024 | SEPTEMBER 7, 2023 DR. FERDAUZIA E. BASTERO Secretes the extracellular bone matrix (includes type-I collagen, proteoglycans, osteocalcin, osteonectin and osteopontin) During active deposition of new matrix, they are arranged as an epithelioid layer of cuboidal or columnar cells on the bone surface. Once surrounded and trapped by their own secretions, the osteoblast becomes a mature bone cell referred to as an osteocyte , imprisoned in lacunae within the newly formed bone matrix. Osteoprogenitor cells are located in the inner Bone normally has a thin layer of unmineralized matrix cellular layer of the periosteum, lining called osteoid. haversian canals, and in the endosteum. Osteoblasts are believed to participate in bone Also these cells can undergo mitotic division resorption by secreting enzymes that remove and have the potential to differentiate into this superficial layer of osteoid, thereby osteoblast. exposing mineralized matrix that can be ➔ This is evident when the population of attacked by the osteoclasts. osteoblasts is depleted in the continual internal remodeling of bone, they are replaced by proliferation and differentiation of the osteoprogenitor cells OSTEOBLASTS Mononucleated cells that are responsible for bone formation OSTEOCYTES Present in the non-continuous lacunae Comes from the osteoblasts Maintains the bone matrix by continuously secreting Calcium salts Figure 3. Osteoblasts of Trabecular bone Retrieved from: (https://vmicro.iusm.iu.edu/virtual_h/34_bl_5.html) derived from osteoprogenitor cells in the periosteum and the bone marrow INTRODUCTION TO MEDICINE 101 | HISTOLOGY LESSON # 4 : BONES AYURA 2027 3 ITM 101 | HISTOLOGY LESSON # 4 - BONES 1st YEAR A.Y. 2023-2024 | SEPTEMBER 7, 2023 DR. FERDAUZIA E. BASTERO secretes Calcium when needed by the body. Note: In pathologic states where uncontrollable actions are happening, Calcium will be secreted even if the body does not need it. Bone forming cells : Osteoblast and the Osteocytes Bone resorption cells : Osteoclasts Figure 4. Osteocytes inside the lacunae Retrieved from: (https://vmicro.iusm.iu.edu/virtual_h/34_bl_5.html) OSTEOCLASTS Throughout life, bone undergoes a continuous process of internal remodeling and renewal that involves removal of bone matrix at multiple sites, followed by its replacement by newly deposited bone. In this process, the agents of bone resorption are the osteoclasts. Largely multinucleated cells Figure 5. Osteocytes of Healing Trabecular bone Retrieved from: (https://vmicro.iusm.iu.edu/virtual_h/34_bl_5.html) Cytoplasm is rich in lysosomes ○ Lysosome breaks down cells/tissues that are used for bone resorption to (TransNote) chisel down the bone to prevent For Interactive learning on Bone Cells: fracturing. Bone resorption also Virtual Microscope Slide: https://vmicro.iusm.iu.edu/virtual_h/34_bl_5.html INTRODUCTION TO MEDICINE 101 | HISTOLOGY LESSON # 4 : BONES AYURA 2027 4