BIOL1XX8 2024 Lecture Notes - Bone Structure and Growth PDF

Support Bone Structure and Growth MEDS1001 _2023 BIOL1008_2023 Associate Professor Michelle McDonald School of MedicalSciences [email protected] I acknowledge and pay my respects to the Gadigal people of the Eora Nation, whose land I walk, work, and gather on every day. The University...

Support Bone Structure and Growth MEDS1001 _2023 BIOL1008_2023 Associate Professor Michelle McDonald School of MedicalSciences [email protected] I acknowledge and pay my respects to the Gadigal people of the Eora Nation, whose land I walk, work, and gather on every day. The University of Sydney Page 1 Fun facts about the skeleton The human body has 206 bones in it, this is reduced from over 300 at birth! Approximately every 11 years your skeleton is completely replaced remodelling The smallest bone is the stapes in the middle ear The longest and heaviest bone is the femur The University of Sydney Page 2 Bone Structure and Maintenance Key Learning Outcomes Understand basic bone structure and matrix components To understand bone remodelling/turnover Why is it important? How is it achieved? Knowledge of the different bone cells Be able to describe how bones grow/develop Develop a strong understanding of osteoporosis, Causes Risk factors Lifestyle Role of exercise The University of Sydney Page 4 The many roles of the skeleton Structural Enable movement Support/form structure Protection for internal organs Homeostasis Storehouse for essential minerals 85% of phosphorus 99% of calcium Houses the bone marrow (heamatopoiesis) Site of energy metabolism Endocrine functions The University of Sydney Page 5 https://open.oregonstate.education/aandp/chapter/6-1-the-functions-of-the-skeletal-system/ Bone Structure Bone Structure Cortical (compact/dense) bone 80% of total bone mass 10% porous Provide strength to structure Cancellous (trabecular/spongy) bone Makes up about 20% of the total bone mass. Highly porous, 50-90% Network of thin porous trabeculae in directions of stress– shock absorption. Provides a large bone surface for mineral exchange The University of Sydney Page 7 Bone Structure The University of Sydney Page 8 Baron R Anatomy and Ultrastructure of Bone in Favus MJ Ed. Collagen and Hydroxyapatite Form Bone Matrix Collagen cross links Provides elasticity Hydroxyapatite crystals Source of Pi and Ca2+ Provides rigidity Bone matrix The University of Sydney Page 9 Bones need to be hard, strong and flexible Collagen Hydroxyapatite crystals Brittle bones Bendy bones The University of Sydney Created with BioRender.com Page 10 Balance Between Collagen and Hydroxyapatite is Essential for Healthy Bone Matrix bone tissue = calcium + protein Normal Without Without calcium protein Created with BioRender.com Page 11 Bone Remodelling Key Functions : Repair damage to skeleton Prevent accumulation of aged tissue/microdamage Supply calcium and phosphorous for mineral homeostasis The University of Sydney Page 12 Bone Remodelling Bone – A Complex Organ The University of Sydney Page 14 Bone Remodelling – The Cycle The University of Sydney Page 15 https://www.frontiersin.org/articles/10.3389/fbioe.2018.00134/full Bone Remodelling – The Cycle The University of Sydney Page 16 https://www.frontiersin.org/articles/10.3389/fbioe.2018.00134/full Bone Remodelling – The Cycle The University of Sydney Page 17 https://www.frontiersin.org/articles/10.3389/fbioe.2018.00134/full Bone Remodelling – The Cycle The University of Sydney Page 18 https://www.frontiersin.org/articles/10.3389/fbioe.2018.00134/full Osteoblasts Form Bone Derived from mesenchymal lineage Forms organic collagen matrix, osteoid, and then mineralizes it Can terminally differentiate into an osteocyte or return to resting bone lining cell Bone Surface The University of Sydney Page 19 P1NP, N-terminal propeptide of type 1 procollagen, P1CP, C-terminal propeptide of type 1 procollagen Osteoblasts Form Bone Osteoblats Collagen bone matrix https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6759523/ P1NP, N-terminal propeptide of type 1 procollagen, P1CP, C-terminal propeptide of type 1 procollagen Osteoclasts Resorb/Degrade Bone Bone surface Derived from hematopoietic pre-cursor cells Resorbs bone matrix by secreting acid to demineralize and proteases to breakdown collagen matrix Liberate minerals into the circulation CTX collagen fiber component cleaved during matrix degradation The University of Sydney CTSK, Cathepsin K. TRAP, Tartrate Resistant Acid Phosphatase. CTX, C-terminal telopeptide of type I collagen, NTX, N-terminal telopeptide of type 1 collagen, PYR, pyridinoline, DPD, deoxypyridinoline Page 21 Osteoclasts Resorb Bone https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7460581/ Osteocytes – Master Regulators of Bone Remodelling The University of Sydney Terminally differentiated osteoblasts embedded within bone Form a canalicular network between each other Releases factors which increase (RANKL) or decrease (OPG) osteoclast formation and activity Mechano-sensing cells – respond to load in tissue – cause for bone loss in space RANK, Receptor Activator of Nuclear Factor KappaB. CTSK, Cathepsin K. TRAP, Tartrate Resistant Acid Phosphatase. CTX, C-terminal telopeptide of type I collagen, Page 23 Osteocytes embed in bone matrix https://pubmed.ncbi.nlm.nih.gov/32512167/ Bone Growth Flat Bones Form via Intramembranous Ossification Protect major organs 1. Mesenchymal cells condense to form connective tissue (No cartilage template) 2. Differentiate to form osteoblasts and form bone spicules 3. Spicules fuse to form trabeculae which then interconnect to form woven bone 4. Mesenchymal cells surrounding trabculae form the periosteum (outer thin layer) 5. Periosteum forms bone collar that mineralises into lamellar bone of cortex of flat bone Long Bone Structure Most long bones have similar structure with Epiphysis (trabecular/spongy bone) Metaphysis (trabecular and cortical) Diaphysis (cortical) Endosteum Periosteum Marrow cavity Major blood supply Long Bones Form via Endochondral Ossification Jennings R, Premanandan C. Veterinary Histology. https://ohiostate.pressbooks.pub/vethisto Long Bones Grow via Endochondral Ossification Joints are cartilaginous at birth Epiphyses ossify in post-natal development Post natal limbs continue to develop until cessation of growth at 13-18 years of age through growth plates Child Adult Long Bones Grow via Endochondral Ossifcation Longitudinal growth involves: Proliferation Chondrocyte proliferation and hypertrophy Calcification of Hypertrophy & calcification Degradation & invasion hypertrophic cartilage and apoptosis Degradation of transverse septa, vascular invasion New bone formation Bone formation on calcified remnants by osteoblasts – primary spongiosa. Osteoporosis Osteoporosis Osteoporosis: characterized by compromised bone structure and strength, predisposing to an increased risk of fracture. Normal Osteoporosis Well-connected or broad band plates of bones. Disrupted, thin or weakened rods. Some of the rods are disconnected. 1 in 3 women and 1 in 5 men over 50 years of age suffer an osteoporotic fracture! The University of Sydney Page 32 Changes in Bone Density with Age The University of Sydney Page 33 Osteoporosis – imbalanced bone remodelling Osteoporosis Healthy The University of Sydney osteoclast osteoblast Page 34 Osteoporosis and Sex Hormones Estrogen: Acts on both osteoclasts and osteoblasts to: ↓ bone resorption and ↑ bone formation. A marked decrease in estrogen during menopause is associated with rapid bone loss via: ↑ bone resorption and ↓ bone formation. Testosterone: Increases bone formation. A source of estrogen Reduces with age → bone loss and fracture The University of Sydney Page 35 https://propelphysiotherapy.com/exercise/decrease-the-risk-of-osteoporosis-with-exercise/ Risk factors for Osteoporosis Primary: Age – older higher Gender - female higher risk (post menopause) Height/BMI – short and frail = higher risk Genetics Lifestyle: Calcium intake Sedentary lifestyle Smoking/medications The University of Sydney Page 36 Lifestyle and Bone Health Exercise that increases bone mass Weight bearing exercise with increasing load will produce the BEST response The University of Sydney https://youtu.be/JLY7JB1Jmgc Page 37 Bone Responds to load/unload Bone loss during spaceflight Bone mass increases in response to load The University of Sydney Page 38 Key Learning Outcomes To understand basic bone structure and matrix components – Cortical, trabecular, hydroxyapatite – rigidity, collagen, elasticity To understand bone remodelling/turnover Why is it important? Maintain integrity, mineral homeostasis, bone shape How is it achieved? Bone resorption followed by new bone formation Knowledge of the different bone cells which maintain bone- osteoblasts, osteoclasts, osteocytes Be able to describe how bones grow/develop – flat bones, long bones, growth pate chondrocytes expand Develop a strong understanding of osteoporosis, Causes – imbalanced remodelling, age, menopause, diet Risk factors –sex, age, genetics, build Lifestyle – diet, sunlight, exercise Role of exercise – response of bone to load The University of Sydney Page 39 Summary bone biology and osteoporosis The University of Sydney https://youtu.be/JLY7JB1Jmgc Page 40 Is this tennis player right or left handed? Left Right https://theconversation.com/what-exercise-does-to-your-bones-57524