Skeletal System - Bones Lecture Notes PDF

MPharm Programme Skeletal System –Bones (1) PHA115 Dr Praveen Bhugra Slide 1 of 34 PHA115 Skeletal System  Learning objectives (The Bone) By the end of this lecture you should be able...

MPharm Programme Skeletal System –Bones (1) PHA115 Dr Praveen Bhugra Slide 1 of 34 PHA115 Skeletal System  Learning objectives (The Bone) By the end of this lecture you should be able to: – Describe the functions of bones – Describe the structure of a long bone – Explain the function of different bone cells – Explain homeostasis in bone cell function – Explain the action of factors affecting bone Slide 2 of 34 PHA115 Skeletal System  The Skeletal System Parts of the skeletal system include: – Bones (skeleton) – Joints – Cartilages – Ligaments Divided into two divisions: 1. Axial: bones around body axis – Examples: skull bones, hyoid, ribs, sternum, vertebrae 2. Appendicular: bones of upper and lower limbs plus shoulder and hip bones that connect them – Examples: collar bone (clavicle), arm (humerus), forearm (radius and ulna), thigh bone (femur) Slide 3 of 34 PHA115 Skeletal System  Functions of Bones 1) Support of the body 2) Protection of soft organs 3) Assistance in movement 4) Mineral homeostasis 5) Blood cell production 6) Triglyceride storage Slide 4 of 34 PHA115 Skeletal System  Bones of the Human Body The adult skeleton has 206 bones Two basic types of bone tissue Compact bone tissue contains few spaces and is arranged in repeating structural units called osteons or haversian systems. Spongy bone tissue formed of trabeculleus bone tissue and does not contain osteons. Slide 5 of 34 PHA115 Skeletal System  Bones of the Human Osteon (Haversian System) – A unit of bone Central (Haversian) canal – Carries blood vessels, nerves and lymphatic vessels Perforating (Volkman’s) canal – Canal perpendicular to the central canal – Carries blood vessels and nerves Slide 6 of 34 PHA115 Skeletal System  Classification of Bones on the Basis of Shape Slide 7 of 34 PHA115 Skeletal System  Classification of Bones Long bones – Typically longer than wide – Have a shaft with heads at both ends – Contain mostly compact bone Examples: Femur, humerus Short bones – Generally cube-shape – Contain mostly spongy bone Examples: Carpals, tarsals Slide 8 of 34 PHA115 Skeletal System  Classification of Bones Flat bones – Thin and flattened, usually curved – Thin layers of compact bone around a layer of spongy bone Examples:, sternum (breastbone), scapulae (shoulder blades), ribs, and most of the skull bones Irregular bones – Irregular in shape – Do not fit into other bone classification categories Example: Vertebrae and hip bones Slide 9 of 34 PHA115 Skeletal System  Gross Anatomy of a Long Bone Diaphysis – Shaft – Composed of compact bone Epiphysis – Ends of the bone – Composed mostly of spongy bone (cancellous) Metaphysis – regions in a mature bone where the diaphysis joins the epiphyses Slide 10 of 34 PHA115 Skeletal System  Structures of a Long Bone Articular cartilage – Covers the external surface of the epiphyses – Made of hyaline cartilage – Decreases friction at joint surfaces Slide 11 of 34 PHA115 Skeletal System  Structures of a Long Bone Periosteum – Outside covering of the diaphysis – Fibrous connective tissue membrane Sharpey’s fibres – Secure periosteum to underlying bone Arteries – Supply bone cells with nutrients Endosteum – membrane lining medullary cavity Slide 12 of 34 PHA115 Skeletal System  Structures of a Long Bone Medullary cavity – Cavity of the shaft – Contains yellow marrow (mostly fat) in adults – Contains red marrow (for blood cell formation) in infants Slide 13 of 34 PHA115 Skeletal System  Bone Markings Surface features of bones – Projections and processes – grow out from the bone surface – Depressions or cavities – indentations Sites of attachments for muscles, tendons, and ligaments Passages for nerves and blood vessels Slide 14 of 34 PHA115 Skeletal System  Types of Bone Cells Osteoblasts: Bone-forming cells Osteocytes : Mature bone cells Osteoclasts: Bone-destroying cells;Break down bone matrix for remodeling and release of calcium Bone remodeling is a process by both osteoblasts and osteoclasts Slide 15 of 34 PHA115 Skeletal System  Types of Bone Cells Osteoblasts Active bone –forming cells that produce collagenase bone matrix Secrete enzyme alkaline phosphatase – promotes deposition of calcium phosphate salts in the matrix to calcify the bone As the bone matrix is formed and calcified the osteoblasts become incorporated within the bone and become transformed into relatively inactive mature bone cells called Osteocytes Osteoclasts Multinucleated cells concerned with bone resorption Remove bone matrix by phagocytosis , dissolve the bone salts and release calcium and phosphate ions in circulation Slide 16 of 34 PHA115 Skeletal System  Bone Formation Known as ossification Timeline ― Initial bone development in embryo and foetus ― Growth of bone into adulthood ― Remodelling: replacement of old bone ― Repair if fractures occur Mesenchyme (early connective tissue) model ― This initial “skeleton” model will be replaced by bone tissue beginning at 6 weeks of embryonic life Slide 17 of 34 PHA115 Skeletal System  Bone Formation Two different methods of ossification each result in similar bone tissue ― Intramembranous: bone forms within sheets of mesenchyme that resemble membranes  Only a few bones form by this process: flat bones of the skull, lower jawbone (mandible), and part of clavicle (collarbone) ― Endochondral: mesenchyme forms hyaline cartilage which then develops into bone  All other bones form by this process Slide 18 of 34 PHA115 Skeletal System  Bone Formation (Intramembranous Ossification) 1) Development of ossification center 2) Calcification 3) Formation of trabeculae 4) Development of the periosteum Slide 19 of 34 PHA115 Skeletal System  Bone Formation (Intramembranous Ossification) 1) Development of ossification center – Mesenchyme cells osteogenic osteoblasts – Osteoblasts secrete organic matrix 2) Calcification: cells become osteocytes – In lacunae they extend cytoplasmic processes to each other – Deposit calcium & other mineral salts 3) Formation of trabeculae (spongy bone) – Blood vessels grow in and red marrow is formed 4) Periosteum covering the bone forms from mesenchyme Slide 20 of 34 PHA115 Skeletal System  Bone Formation (Endochondral Ossification) 1) Development of 2) Growth of cartilage 3) Development of 4) Development of cartilage model model primary ossification medullary cavity 6) Formation of 5) Development articular of Secondary cartilage and ossification epiphyseal plate Slide 21 of 34 PHA115 Skeletal System  Bone Formation (Endochondral Ossification) 1) Development of cartilage model of the “bone” ― As mesenchyme cells develop into chondroblasts 2) Growth of cartilage model ― Cartilage “bone” grows as chondroblasts secrete cartilage matrix ― Chondrocytes increase in size, matrix around them calcifies ― Chondrocytes die as they are cut off from nutrients, leaving small spaces (lacunae) Slide 22 of 34 PHA115 Skeletal System  Bone Formation (Endochondral Ossification) 3) Development of Primary ossification center – Perichondrium sends nutrient artery inwards into disintegrating cartilage – Osteogenic cells in perichondrium become osteoblasts that deposit bony matrix over remnants of calcified cartilage and the spongy bone forms in center of the model – As perichondrium starts to form bone, the membrane is called periosteum Slide 23 of 34 PHA115 Skeletal System  Bone Formation (Endochondral Ossification) 4) Development of medullary (marrow) cavity – Spongy bone in center of the model grows towards ends of model – Octeoclasts break down some of new spongy bone forming a cavity (marrow) through most of diaphysis – Most of the wall of the diaphysis is replaced by a collar of compact bone Slide 24 of 34 PHA115 Skeletal System  Bone Formation (Endochondral Ossification) 5) Development of secondary ossification center – Similar to step 3 except that nutrient arteries enter ends (epiphyses) of bones and osteoblasts deposit bony matrix spongy bone forms in epiphyses from center outwards – Occurs about time of birth 6) Formation of articular cartilage and epiphyseal cartilage – Hyaline cartilage at ends of epiphyses becomes articular cartilage – Epiphyseal (growth) plate of cartilage remains between epiphysis and diaphysis until bone growth ceases Slide 25 of 34 PHA115 Skeletal System  Changes in the Human Skeleton In embryos, the skeleton is primarily hyaline cartilage During development, much of this cartilage is replaced by bone Cartilage remains in isolated areas – Bridge of the nose – Parts of ribs – Joints Slide 26 of 34 PHA115 Skeletal System  Bone Growth Epiphyseal plates allow for growth of long bone during childhood – New cartilage is continuously formed – Older cartilage becomes ossified Cartilage is broken down Bone replaces cartilage Slide 27 of 34 PHA115 Skeletal System  Bone Growth Bones are remodeled and lengthened until growth stops – Bones change shape somewhat – Bones grow in width Slide 28 of 34 PHA115 Skeletal System  Homeostasis in Bone Bone Resorption – action of osteoclasts and parathyroid hormone (PTH) Bone Deposition – action of osteoblasts and calcitonin Occurs by direction of the thyroid and parathyroid glands Slide 29 of 34 PHA115 Skeletal System  Homeostasis in Bone Blood levels of Ca2+ controlled Negative feedback loops Parathyroid hormone (PTH) increases osteoclast activity and also decreases loss of Ca2+ in urine Calcitonin decreases osteoclast activity Slide 30 of 34 PHA115 Skeletal System  Homeostasis in Bone Bone tissue has the ability to alter its strength in response to changes in mechanical stress. Under stress, bone tissue becomes stronger through increased deposition of mineral salts and production of collagen fibres by osteoblasts Without mechanical stress, bone does not remodel normally because bone resorption occurs more quickly than bone formation. Main mechanical stresses on bone are those that result from the pull of skeletal muscles and the pull of gravity. Slide 31 of 34 PHA115 Skeletal System  Factors Necessary for Bone Development, Growth and Repair Adequate minerals (Ca, P, Mg) Vitamins A, C, D Hormones – Before puberty: hGH + insulin-like growth factors – Thyroid hormone and insulin also required – Sex hormones contribute to adolescent growth spurt Weight-bearing activity Slide 32 of 34 PHA115 Skeletal System  Factors Affecting Bone Development, Growth and Repair Deficiency of Vitamin A – retards bone development Deficiency of Vitamin C – results in fragile bones Deficiency of Vitamin D – rickets, osteomalacia Insufficient Growth Hormone – dwarfism Excessive Growth Hormone – gigantism, acromegaly Insufficient Thyroid Hormone – delays bone growth Sex Hormones – promote bone formation; stimulate ossification of epiphyseal plates Physical Stress – stimulates bone growth Glucocorticoids – activate osteoclasts and resorption of bone Slide 33 of 34 PHA115 Skeletal System  Further Reading Refer to the Following Textbooks Ross and Wilson Anatomy and Physiology in Health and illness 13th Edition Gerard J. Tortora and Byran H. Derrickson Principles of Anatomy and Physiology 13th Edition Frederic H. Martini Fundamentals of Anatomy & Physiology 7th Edition Elaine N. Marieb and Katja Hoehn Human Anatomy & Physiology 8th Edition VanPutte, Regan and Russo Seeley’s Anatomy and Physiology 12th Edition Slide 34 of 34 PHA115 Skeletal System