Basic Osteology Lecture Notes PDF

Basic Osteology Dr Stamatia Papathanasiou [email protected] 1 1  This lecture will cover…  Explain the bone histology of compact bone: What is the harversian system and what are osteons  Describe the bone histolo...

Basic Osteology Dr Stamatia Papathanasiou [email protected] 1 1  This lecture will cover…  Explain the bone histology of compact bone: What is the harversian system and what are osteons  Describe the bone histology of cancellous bone. Specifically, you need to be able to describe the structure and function  Explain the composition and functions of bone  Define and explain the following types of bone cells;  Osteoprogenitor Cells  Osteoblasts  Osteocytes  Osteoclasts  Explain the process of bone growth  Explain the process of Intramembranous ossification  Explain the process of Endochondral ossification  Explain the factors which affect the growth of bone 2 2  Types of Skeleton Endoskeleton Exoskeleton 3 3  How many bones the human body has? 4 4  Number of Bones in the Human Body Axial skeleton – skull/face, vertebral column and thorax. Appendicular skeleton – shoulder girdle, upper extremities, pelvic girdle, and lower extremities. 5 5  What are the functions of the skeletal system? 6 6  Skeletal System Axial Skeleton Appendicular skeleton 7 7  Axial Appendicular skeleton skeleton Skull Upper bones (29) limbs (64) Vertebral Lower column limbs (62) (26) Thoracic cage (25) 8 8  Axial Skeleton  Skull 29 bones Cranium 8 bones Face 14 bones Hyoid 1 bone Ossicles 6 bones 9 9   Vertebral column 26 bones Cervical vertebrae 7 bones Thoracic vertebrae 12 bones Lumbar vertebrae 5 bones Sacrum 1 bone (5 fused) Coccyx 1 bone (3 – 5 fused or partially fused) 10 10   Thorax 25 bones Sternum 1 bone Ribs 24 bones 11 11  Appendicular Skeleton  Shoulder girdle 4 bones Clavicle 2 bones Scapulae 2 bones 12 12   Upper extremity 60 bones Humerus 2 bones Ulna 2 bones Radius 2 bones Carpals 16 bones Metacarpals 10 bones Phalanges 28 bones 13 13   Pelvic girdle 2 bones Innominate bone 2 bones (Each consists of 3 fused bones– ilium, ischium, and pubis) 14 14   Lower extremity 60 bones Femur 2 bones Fibula 2 bones Tibia 2 bones Patella 2 bones Tarsus 14 bones Metatarsus 10 bones Phalanges 28 bones 15 15  Types of Bone  Long bones  Short bones  Flat bones  Irregular bones  Sesamoid bones 16 16  1 10 2 11 12 3 13 4 14 15 5 16 17 6 7 8 9 18 19 20 21 22 23 24 17 17  Microanatomy of bone The bone tissue comprises four main types of bone cells:  Osteogenic cells  Osteoblasts  Osteocytes  Osteoclasts 18 18  Bone Cells  Osteoprogenitor Cells – stem cells of bone  Found on the inner lining of periosteum and endosteum 19 19  Bone Cells  Osteoblasts – secretory cells, found on the surface of the bone matrix. Osteoblasts are bone producing cells.  Secrete bone matrix and alkaline phosphatase which calcifies matrix 20 20  Bone Cells  Osteocytes – Osteocytes are derived from osteoblasts and have a function in the daily metabolism of bone tissue  These are mature osteoblasts trapped in lacunae between the layers of lamellae in cortical bone  They have fine cytoplasmic processes which project into the canaliculi  They moderate short term fluctuations in of serum calcium and phosphate levels 21 21  Bone Cells  Osteoclasts – Osteoclasts are bone resorption cells.  These cells contain many lysosomes and secrete substances which break down bone matrix and phagocytose the remains. 22 22  Composition of bone The composition of the material (osseous tissue) which makes up bone consists of widely separated cells surrounded by large amounts of intercellular substance 23 23  Composition of bone  This bone matrix is formed from an organic material called OSTEOID which consists of a ground substance of proteoglycans and a protein scaffold of Type I collagen fibres.  Osteoid gives bone its tensile strength 24 24  Composition of bone  Crystals of inorganic mineral salts attach themselves to the collagen fibres which gives bone its incredible strength and hardness without being brittle  These mineral salts of calcium phosphate, carbonate and hydroxide are collectively called CALCIUM HYDROXYAPETITE 25 25  Bone Histology An adult long bone 26 26  Bone Histology  1. Woven bone – fragile bone found in stages of bone formation and repair  2. Lamellar bone  Compact or cortical bone which covers spongy bone and shafts of long bones (protects and supports)  Cancellous or spongy (trabecular) bone which forms the ends of long bones and the inner mass of many others (provides support and stores RBM) 27 27  Bone Histology  Compact bone consists of structural units called HAVERSIAN SYSTEMs or OSTEONs arranged in a regular fashion 28 28  Bone Histology  Cancellous bone is unorganised extensions of bone tissue around the bone-marrow spaces 29 29  Bone Type Distribution 30 30  Bone Structure  Compact Bone  Composed of many osteons in a regular fashion  Form concentric ring structure OSTEON 31 31  Bone Structure  Cross section through an osteon 32 32  Compact Bone  Central (Haversian) Canal 33 33  Compact Bone  Concentric lamellae (rings of hard calcified intercellular substance) 34 34  Compact Bone Lacunae (spaces containing osteocytes) 35 35  Compact Bone CANALICULI  Tiny canals radiating out from lacunae, containing slender processes of osteocytes  Connect with surrounding lacunae and central canal 36 36  Compact Bone  Running at 90 degrees to the central canal are channels called Volkmann`s canals 37 37  Compact Bone Volkmann`s canals  Connect blood vessels from the PERIOSTEUM with those of Haversian system and medullary cavity 38 38  Bone structure Name these structures a b c d 39 39  Cancellous or Spongy Bone  An irregular lattice work of thin plates called TRABCULAE  They are nourished by red bone marrow 40 40  Bone Growth and Development  Long bones begin as cartilage. The centre ossifies then the ends, leaving a strip of specialised growing cartilage in between 41 41  Ossification  Primary ossification centres formed during intrauterine life or just after e.g. shaft of long bone.  Secondary ossification centres appear at different times of the child’s development. 42 42  Anatomy of the long bone  Periosteum: This is the fibrous membrane that covers the exterior of each bone. The periosteum functions to help with fracture repair, to nourish and protect the bone, and to act as an attachment point for tendons and ligaments.  Endosteum: this is a thin layer of cells and connective tissues that covers the internal bone surfaces facing the medullary cavity. This membranous layer covers the trabeculae of spongy bone and also lines the canals that pass through the cortical bone.  Like the periosteum, the endosteum has a rich neurovascular supply and contains both osteoblasts and osteoclasts.  Diaphysis: it is a long, cylindrical structure/bone which forms the main shaft of the long bone. The central part is hollowed to form the medullary cavity or the marrow cavity.  Metaphysis: The metaphysis are regions of bone found between the diaphysis and epiphyses of long bones. During the growth of a bone, a thin layer of hyaline cartilage known as the epiphyseal plate in this region which allows the shaft to grow in length.  Epiphysis: this is the rounded parts located at the proximal and distal ends of a long bone. The interior of each epiphysis is filled with spongy trabecular bone containing red bone marrow. The exterior surface of the epiphyses is covered in compact bone in order to protect the fragile, spongy tissue below it. 43 43  The Growing Long Bone DIAPHYSIS– or shaft 44 44  The Growing Long Bone The diaphysis contains the MEDULLARY CAVITY which contains bone marrow The cavity is lined with a thin membrane called the END- OSTEUM the site of osteoblasts and osteoclasts 45 45  The Growing Long Bone EPIPHYSIS – ends of the long bone composed of cancellous bone 46 46  The Growing Long Bone EPIPHYSEAL GROWTH PLATE – a plate of hyaline cartilage separates the epiphysis from the rest of the bone Growth of bone length occurs at this point 47 47  The Growing Long Bone The METAPHYSIS the region proximal to the growth plate where ossification occurs 48 48  The Growing Long Bone  The PERIOSTEUM – a tough fibrous connective tissue covers the bone except for the articular surfaces 49 49  The Growing Long Bone  This consists of an outer layer containing nutrient arteries and nerves and an inner layer of osteoblasts which assists in the growth of girth of the bone 50 50  The Growing Long Bone  The inner layer is attached to bone by collagen fibres called SHARPEY’S FIBRES  The periosteum protects underlying bone and provides attachment for muscles and ligaments 51 51  The Growing Long Bone Articular surfaces are covered with ARTICULAR HYALINE CARTILAGE 52 52  The Growing Long Bone 53 53  Bone  Cortical bone 54 54  Bone  Cancellous bone 55 55  Bone  Epiphyseal growth plate 56 56  Bone Growth  The Epiphyseal Growth Plate 57 57  Bone Growth 58 58  Bone Growth 59 59  Bone Growth  Germinal and proliferating zone where new chondrocytes are developed and form a cartilage matrix 60 60  Bone Growth  Zone of maturation and hypertrophy where cells form pallisades and enlarge 61 61  Bone Growth  Zone of Calcification where the matrix around the chondrocytes calcify and the trapped cells die 62 62  Bone Growth  Zone of ossification where osteoblasts arrive from the metaphyseal blood supply and secrete osteoid 63 63  Ossification  The process by which bones form in the body  The potential skeleton of the human embryo is composed of fibrous membranes and hyaline cartilage 64 64  Ossification  Begins at around 6th or 7th month  Intramembranous ossification  Endochondral ossification 65 65  Intramembranous Ossification  Ossification occurs in membranes  Forms cancellous bone  Flat skull bones and clavicles form in this way 66 66  Endochondral Ossification  Ossification occurs in rods of cartilage  Forms long bones 67 67  1.Cartilage template surrounded by perichondrium 68 68  2. Bony collar forms 69 69  3. Primary ossification centre forms 70 70  4. Blood vessels enter 71 71  5. Marrow cavity forms 72 72  6. Thickening and lengthen -ing of collar (this becomes the diaphysis) 73 73  7.Formation of secondary ossification centres (this becomes the epiphysis) 74 74  8.Remains of cartilage as articular cartilage and epiphyseal plate 75 75  9. Epiphyseal closure 76 76  Can you think of factors that could affect the bone growth? 77 77  Identify the steps of bone repair:  Bone repair (remodeling) usually occurs where there is a injured bone or areas in need of extra strength; the process encourages the protection of bone tissue and renewal of old bone tissue (around a fractured bone).  The bones in our body are active tissues which is why they are always being remodeled. E.g., the femur shaft may not always be restored completely (and rather changes very slowly) , but the distal end of the femur is repaired every 5-6 months.  Bone repair occurs in four different stages which may take several months to be completely healed. If it’s a plain fracture, it would take up to 3-4 weeks, however this may change depending on the location, angle, severity and the type of fracture.  In approx. 5% of total bone mass, bone repair takes place. However, around distinct parts of the body, the rates will vary. Bones are able to get thicker and stronger when subjected to stress (due to bone remodeling), but bones like a limb in a cast isn’t subject to normal stress and therefore will eventually lose its mass. 78 78  Bone repair 1. Fracture Hematoma Formation 2. Fibrocartilaginous Callus Formation 3. Formation of Bony Callus 4. Bone remodelling 79 79  Bone repair includes 4 main stages such as: 1) Fracture Hematoma Formation: When a bone is fractured or breaks, the blood vessels surrounding the bone and periosteum (the membrane covering the outer surface of bones) are damaged. This causes blood to hemorrhage ( blood escaping from ruptured vessels) into the surrounding area. This then results in the formation of hematoma (clotted blood) at the fractured site within 6-8 hours; producing the constriction of blood vessels (preventing any further bleeding). Clotting allows the damaged blood vessels at the broken ends of the bone to seal. Due to the hematoma forming, blood cells end up lacking nutrients and thus die, causing inflammation around the fractured area. The phagocytic cells will remove the dead cells from the area. 2) Fibrocartilaginous Callus Formation: Fibroblasts (cells in connective tissues that produce collagen and other fibers) enter the site of fracture from the periosteum and replicate. The collagen fibers are then produced and distributed with small blood vessels as well as inflammatory cells; this will form the granulation tissue (a newly created connective tissue). Osteoblasts will form the spongy bone. Due to the formation of granulation tissue, a fibrocartilaginous callus (a temporary repair tissue consisting of many collagen fibers and cartilage) is generated. 80 80  3) Formation of Bony Callus The region of the fracture is provided with vascular tissue, as additional connective tissue stem cells and new blood vessels invade the soft callus. The osteogenic cell develops to osteoblasts and moves towards the fibrocartilaginous callus. Spongy/soft bone is on the inside and outside surfaces, joining the broken bones together. This process may take several months for the broken ends of the bone to firmly join after the fracture. Over time the area of fibrocartilaginous callus is converted into spongy bone forming bony callus. 4) Bone remodelling The final stage is bone remodelling , where the osteoclasts increases in area as it removes any damaged or dead cells around the bony callus. Spongy bone or medullary cavity is replaced with compact bone. This creates a stable, strong and thick area of bone, where the fracture was. Over time the bone should correctly align- repairing the bone. 81 81  Synovial Joints  Joint cavity with bones connected and contained by joint capsule 82 82  Synovial Joints  Bone ends covered with hyaline cartilage 83 83  Synovial Joints  Joint capsule is lined by synovial membrane which also covers intra- capsular structures 84 84  Synovial Joints  Joint cavity contains synovial fluid which nourishes and lubricates cartilage 85 85  Synovial Joints  Pouches of synovial fluid called bursae are found connected to the joint and function as cushions 86 86  Synovial Joints  Synovial fluid contains fats, sugars, serum and hyaluronic acid 87 87  Synovial Joints  Joints are supported by ligaments which joint bone to bone and tendons which join bone to muscle n.b. tendon sheath 88 88  School of Health & Psychological Sciences City St George’s, University of London Northampton Square London EC1V 0HB United Kingdom T: +44 (0)20 7040 5060 E: [email protected] www.city.ac.uk/department Thank you! 89 89