Skeletal System 1 PDF

Principles of Human Structure Skeletal System 1 Dr Siobhain O’ Mahony  Learning Objectives List and compare the major types of cartilage based on structure, function, and location. List and explain the main functions of the bony skeleton. Class...

Principles of Human Structure Skeletal System 1 Dr Siobhain O’ Mahony  Learning Objectives List and compare the major types of cartilage based on structure, function, and location. List and explain the main functions of the bony skeleton. Classify bones according to shape; include several bony examples for each category. Explain why bones are considered organs. Select a specific bone, such as the femur, and discuss the tissues comprising it. Describe the gross anatomy of a typical long bone, and compare it to that of a typical flat bone. Compare the microscopic structure of compact and spongy bone. Discuss the components of the extracellular matrix and each of the important cell types found within bone tissue. Explain how bones withstand tension and compression; point out the role of compression lines and tension lines. Distinguish between two types of bone formation: intramembranous and endochondral ossification. Identify the basic steps in the healing of a bone fracture. Know the axial and appendicular skeletons  Skeletal System Framework of Cartilage and Bones (organs) interrupted by Joints Axial Skeleton Appendicular Skeleton Bones are more than just racks to hang muscles from- – Support weight – Work with muscles to produce controlled and precise movements – Muscles pull against skeleton to make us sit, walk, run Fig. 7.1 Tortora 10th ed.  Cartilage Connective tissue Collagen and / or elastic fibres in gel-like structure Chondrocytes (cells) in lacunae (cavities) No nerves or blood vessels Sometimes surrounded by perichondrium – Absent in articular and Fibro cartilage – Connective tissue composed of fibroblasts (outer layer) and chondroblasts (precursors to chondrocytes, inner layer) – Acts to support the cartilage Hyaline: – Most common – Fine fibres in a gel-like matrix Fig. 6.1 Marieb – Found in most articulations E.g. most joints Fibrocartilage – Large bundles of collagen – Resists compression and tension forces E.g. anulus fibrosus Elastic – Matrix of elastic fibres – Where flexibility is needed E.g. epiglottis  Bones Bones as organs are made up of Functions of Bones – Connective tissue: – Support Bone, cartilage, adipose, blood Framework to support the body weight and attachment of soft tissue – Epithelial tissue Blood vessels – Movement Lever system to help muscles generating movement-large range – Nervous tissue Nerves – Protection Skull, rib cage, vertebral column, pelvis – Mineral Storage Calcium and phosphate Can be released in the blood stream – Blood cell production and energy storage Red, white blood cells-red bone marrow – Energy metabolism Hormone- Osteocalcin produced by bone cells (osteoblasts) influences bone production, fat storage and stimulates insulin production  Types of Bones Flat bones Long bones – Thin layers of compact bone surrounding spongy – Elongated shape bone (diploë) Limbs, Fingers, Toes roof of skull, ribs, sternum, scapula Short bones – Roughly cuboidal shape Sutural bones Carpals, Tarsals – Oddly shaped bones inserted between flat bones Sesamoid of skull – Present within tendons Structurally they are flat bones Patella Pneumatized bones Irregular bones – Hollow bones or containing air pockets – Shape varies Vertebrae, some facial bones, Heel bone Ethmoid Fig. 5.11 Martini  Anatomy of a long bone e.g. femur and tibia-subjected to load and crucial for skeletal mobility Fig. 6.2 Tortora Fig. 6.4 Marieb  Structure of short, irregular & flat bones External layers of compact bone covered by periosteum – Internal and external tables Internal layer of spongy bone (diploë) covered by endosteum Bone marrow is present but there is no marrow cavity Blood vessels and nerves similar to long bones  Composition of Bone Tissue Abundant extracellular matrix containing widely separated cells Matrix: 15% water, 30% collagen fibres, 55% minerals – Collagen fibres provide elasticity – Mineral salts provide rigidity Hydroxyapatite, calcium phosphate, magnesium, fluoride, potassium, sulfate – Collagen fibres provide an organic framework on which crystals can form Allows bone to strong, somewhat flexible and highly resistant to shattering Cells present in bone tissue – Osteogenic (osteoprogenitor) cells: Unspecialised bone cells, only bone cells to divide, found in inner and outer lining of bones (endosteum and periosteum) – Osteoblasts: Bone building cells, secrete collagen fibres and initiate calcification, will surround itself with matrix and become osteocyte- osteogenesis – Osteocytes: Main cell in healthy bone, maintenance and metabolism – Osteoclasts: Derived from white blood cells, concentrated in the endosteum, active in bone growth and remodelling as well as resorption which regulates calcium levels-remove and recycle bone Fig. 6.3 Tortora  Compact bone External layer (cortex) Osteons or Haversian systems – Lamella Provides strength and support – Canaliculus – Central canal – Osteocyte Fig. 6.4 Tortora  Spongy bone tissue Internal layer Trabecula with no central canal, osteocytes in lacunae receive nutrients from blood vessels of the endosteum by diffusion Reduces weight of bones Supports and protects red bone marrow Present in areas receiving lighter stress Trabeculae arranged along lines of stress Fig. 6.4 Tortora  Periosteum and Endosteum Periosteum – Composed of outer fibrous layer and inner cellular layer (osteoprogenitor cells). – Periosteum is absent in sesamoid bones. Also absent at attachment of tendons, ligaments, joint structures and articular cartilage. – Its functions are: isolate and protect the bone from surrounding tissues provide a route and a place of attachment for circulatory and nervous supply participate in bone growth and repair attach the bone to the connective tissue network of the deep fascia Endosteum – Single layer of osteoprogenitor cells – Active in growth and remodelling – Covers trabeculae in the medullary cavity or the central canal of osteons. – Not always continuous Fig. 5.4 Martini  Blood and Nerve Supply Diaphysis – Nutrient Foramen (usually one or a few) Nutrient Artery Nutrient Vein Epiphysis and Metaphysis – Several veins and arteries penetrating through several foramina Periosteum & outer part – Many small veins and arteries (branches from the nutrient vein and artery) – Perforating canals Nerve supply follows veins and arteries – Sensory nerves – Large amount of ending in periosteum and cortical bone make fractures painful Fig. 6.5 Tortora  Forces at work Compact and spongy bone tissues are aligned along lines of stress – Compact bone is thicker where forces are greater, the mesh of spongy bone is also oriented to counteract stress – Spongy bone is more appropriate for multidirectional tension Fig. 6.6 Marieb Change throughout life - remodelling  Bone surface markings Bones develop surface markings offering anchor points for tendons and ligaments as muscles are being used (tension and compression forces change the topography) – Usually not present at birth Other markings allow the passage of nerves and blood vessels and are present from birth. From Tortora Bone Formation – Endochondral Ossification Mesenchymal cells=can differentiate into a variety of cell types Osteoblasts = bone cells Chondrocytes = cartilage cells Osteoclasts=breakdown bones Fig. 6.7 Tortora Fig. 5.6 Martini Bone Formation - Intramembranous ossification When osteoblasts differentiate within mesenchymal or fibrous connective tissue-also called dermis ossification- occurs in deeper layers of the dermis- bones that result are dermal bones Flat bones of the skull Facial bones Fig. 6.6 Tortora Mandible Medial part of clavicle  Bone Growth (length) 5 4 1.On the epiphyseal side, anchors the epiphyseal plate to the epiphysis 3 2.Chondrocytes divide and form columns 3.Chondrocytes enlarge and start producing a calcified matrix 2 4.Chondrocytes die because the matrix has calcified 5.Osteoclasts dissolve the calcified cartilage and osteoblasts and blood vessels from the 1 diaphysis invade the area to form new bone. 6.After adolescence, the epiphyseal plate becomes ossified, stopping growth. Fig. 6.8 Tortora  Bone growth (thickness) 1. Periosteal cells differentiate into osteoblasts and produce bone matrix creating ridges around blood vessels. 2. Ridges grow and fuse, forming a canal surrounding blood vessel. The periosteum becomes endosteum. 3. Osteoblasts of the new endosteum form new lamellae, closing the canal. 4. The new osteon is formed and new circumferential lamellae are formed, creating new ridges. Fig. 6.9 Tortora