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WHERE AM I? Online Anatomy Module 1 INTRO & TERMS CELL EPITHELIUM BONE MUSCLE NERVOUS SYSTEM AXIAL SKELETON APPENDICULAR SKELETON MUSCLES EMBRYOLOGY BONE Bone is the hard supporting tissue that is used to make the very many bones of the skeleton: small, large; long, short; flat, rounded Bones come together and are held at joints which allow (& restrict) movement Muscles act across joints to cause particular movements, which are classified in relation to the planes of the body - flexion, abduction, rotation, etc. at that joint, e.g., extension of the knee to kick ENJOYABLE LIFE - - bones as the means to do things; extended by the use of tools & devices LIFE & ENJOYABLE LIFE: The BONE Connection First things first - the most important activities: BREATHE - respiratory muscles contract & relax CIRCULATE BLOOD - heart & vessel muscles contract muscle contractions driven or timed by rhythm generators in the brain Nerve-cell firing & signaling + muscle contraction & relaxation need Calcium ion Blood Ca2+ level is held to a very precise and limited range WHAT GUARANTEES Ca2+ STAYS AT THIS LEVEL A very large store bone is about half crystalline calcium salts (hydroxyapatite/bone mineral) A way to get Ca2+ out of storage cells that eat away bone & put its salts back into solution A way to get Ca2+ into storage cells that make bone and build in the calcium salts Ways to get Ca2+ for the body calcium in the diet; absorbed in the gut; not lost by the kidneys into the urine Ways to control the blood level hormones WHAT GUARANTEES Ca2+ STAYS AT THIS LEVEL A very large store bones are about half mineral To get Ca2+ out of storage cells that eat away bone & put its salts back into solution - OSTEOCLASTS To get Ca2+ into storage cells that make bone and build in the calcium salts OSTEOBLASTS Ways to get Ca2+ for the body calcium in diet; absorbed in the gut; not lost by the kidneys To control the blood level hormones & helper materials (e.g. vitamin D, cytokines); use SOME IDEAS 1 1 Bone is a hard material. How do cells make something this hard? 2 Cells synthesize and release to their exterior materials that will assemble to a strong, but soft substrate - densely packed string-like collagen fibers (fibril is the term used because they are small) 3 Also secreted outside the cell into the ECM/extracellular matrix (extra=outside) are other molecules that cause calcium, phosphate, hydroxyl and opther ions to precipitate as fine hydroxyapatite crystals 4 The densely packed fibrils make bone matrix strong; the mineral crystals, also densely arranged, confer hardness SOME IDEAS 2 1 Construction/formation of bone is slower than destruction/resorption 2 Construction & destruction need to be in balance, or bone is lost 3 Many organs have to work together: gut, bone, kidney, skin, endocrine glands, muscles & nerves 4 Complicated & vulnerable control systems 5 Some aspects under person’s control -- exercise, diet, lactation; many things are not: genes, sex, age, size PURPOSE OF THE SKELETON 1 Mineral store for Ca2+ 2 Protection skull - brain, eyes cord heart vessels bone marrow spine - spinal rib cage lungs, great bone - Calls for a living, hard, strong material with Ca in it } 3 Support & leverage SKELETON -- many bones, connected by joints (with ligaments), pulled on by muscles, covered by skin & fat ENJOYABLE LIFE - - bones as the means to do things; extended by the use of tools & devices PURPOSE OF THE SKELETON: Correlates 1 Mineral store for Ca2+ 2 Protection skull, marrow etc 3 Support & leverage BONE MATERIAL/MATRIX STRONG - densely packed-in collagen fibrils HARD - calcium hydroxyapatite mineral crystals LIVING - osteocytes/bone cells living in spaces/lacunae & extending long processes in canaliculi Contrast tooth enamel - 98 % mineral so very hard, but brittle Where the bone cell lives LACUNA (hole) for OSTEOCYTE BODY MATRIX CANALICULUS (tiny channel) for Gap junction contact with next osteocyte OSTEOCYTE PROCESS EXTRACELLULAR MATRIX ECM 3 Cells create and achieve control over their environment by synthesizing combinations of types of macromolecule which interact outside the cells Cartilage collagens II & Resilient firmness in joint, airway, IX aggregated proteoglycans link & fetal-skeletal cartilages proteins & hyaluronan cartilage glycoproteins Collagens I & XII Resilient hardness of bone bone proteoglycans bone glycoproteins mineral crystals STRUCTURES OF A WORKING JOINT Articular cartilage Marrow Joint space with synovium Bone Joint capsule Ligament Tendon Nerve Muscle Periosteum dense irregular HARD/IMPOSSIBLE TO MOVE & ENJOY LIFE WHEN Joints get inflamed Cartilage wears out Bones break Bones grow out of shape Muscles weak or painful Brain, cord or nerves injured (paralysis) Articular cartilage absorbs & spreads the load Marrow Joint space with synovium Bone Joint capsule Ligament Tendon Nerve Muscle Periosteum dense irregular BONE REGIONS & TYPES Joint capsule EPIPHYSIS DIAPHYSIS/ SHAFT Periosteum marrow Joint cartilage absorbs and spreads load Spongy bone with struts/ trabeculae Dense bone BONE SURFACES Fibrous Periosteum Osteoblastic vessels marrow Joint cartilage Spongy bone with struts/ trabeculae Dense bone Inner surfaces of both types lined by ENDOSTEUM of resting cells, active osteoblasts, & osteoclasts Endo = inside Peri = around BONE COMPONENTS Joint capsule EPIPHYSIS DIAPHYSIS/ SHAFT Fibrous Periosteum Osteoblastic vessels marrow Joint cartilage Spongy bone with absorbs struts/ trabeculae Dense bone and spreads Inner surfaces of both types lined by ENDOSTEUM load of resting cells, active osteoblasts, & osteoclasts Bone matrix = collagen fibrils + mineral crystals BONE CELLS Active Osteoblasts Bone canal vessels Periosteum Osteoclast Resting cells Osteocyte Ca 2+ Osteon/Haversian system with concentric lamellar/layered bone DENSE BONE REMODELING Osteoblasts filling in the tunnel New bone start of new osteon Osteoclasts as a team eating out a resorption tunnel BALANCE is vital in bone - bone destroyed by osteoclasts has to be replaced close by with new bone made by osteoblasts 1 Everything has to be done by cells* 2 Organs & tissues need to grow & to change shape 3 Cells age , and control systems get out of balance 4 Bone is always at the mercy of body’s need for calcium - nerve-muscle priority 5 Bone needs to be loaded every day: use is essential BONE’S PROBLEMS 1 Everything has to be done by cells* 2 Organs & tissues need to grow & to change shape 3 Cells age , and control systems get out of balance 4 Bone is always at the mercy of body’s need for calcium nerve-muscle priority 5 Bone needs to be loaded every day: use is essential * Cells die & may not be replaced Cells cannot respond to signals Cells do not send signals Supplies, e.g. of Ca , not adequate Growth more demanding than staying the same DENSE BONE at less risk than spongy bone 1 A lot of bone to start with (less in women) 2 Only a few tunnels made by osteoclasts 3 Tunnels filled in at least a little by new bone DENSE BONE OSTEOCLAST-osteoblast imbalance leads to somewhat weaker bone Larger holes Narrower SPONGY BONE at more risk than dense bone 1 Struts are thin to start with ~ weak 2 Much surface area for attack by osteoclasts 3 Gap in a strut/trabecula cut right through is usually too wide to be bridged by any new bone SPONGY BONE OSTEOCLAST- osteoblast imbalance & architecture lead to fragile bone Thinner struts Bigger holes Fewer struts = much weaker framework MAINLY SPONGY BONE LOSS causes fractures in 1 Bones that are mostly spongy, e.g. vertebra compression fracture 2 Spongy part of long bones where leverage “Wrist” end concentrates loading of radius “Hip” fracture at neck of femur from falling on the hand FRACTURES KILL Lung embolism - clot(s) not stopped until lungs’ arteries Infections - pneumonia, etc Falls get Granma sent to a “home”, where she is too depressed to live How to get a better cell-activity balance 1 Get more bone built when young food, exercise, vitamin D (sunlight) 2 Keep on eating properly, & boost needed nutrients when older, or pregnant 3 Exercise - high rapid loads, as well as lengthy lower loadings 4 Correct hormone deficiences - older women especially 5 If at risk, have bone density measurements taken, with a view to special drug therapy Osteoblasts filling in the tunnel New bone DENSE BONE REMODELING* REMODELING Eaten-out hole is a Howship’s lacuna Sealing ring of tight attachment to bone Osteoclast Ruffled border agitating released enzymes & acid Osteoclasts as a team eating Un-mineralized OSTEOID between out a resorption tunnel active osteoblasts & calcified bone INTRAMEMBRANOUS OSTEOGENESIS Osteoblast Mesenchyme Condensation Differentiation Osteoid deposition Osteocyte incorporation INTRAMEMBRANOUS OSTEOGENESIS Condensations are widely dispersed and separated to commit a territory to becoming bone Mesenchyme Vessels present Continued division & recruitment to osteoblast numbers Mesenchyme INTRAMEMBRANOUS OSTEOGENESIS LESS ACTIVE CELLS OSTEOCLAST TRABECULA OSTEOID ACTIVE OSTEOBLASTS Mesenchyme later turns into marrow IM & EC OSTEOGENESIS Vessels : incorporated from the start & remodel with the bone TRABECULAE thicken by division & recruitment of more osteoblasts to increase bone density OSTEOCLASTS active from the start to remodel & reshape the bone SKELETON & CARTILAGE Cartilage provides some flexibility & recovery of shape at critical places Cartilage participates as pieces that develop, and stay attached to the skeleton Other cartilage develops with bones (indeed, it precedes the bone), then remains at the ends to make the joint surface or articular cartilage Facial and skull vault/dome bones form with negligible cartilage present ENDOCHONDRAL OSTEOGENESIS Recognizable, if some of the trabeculae have cores of calcified cartilage SKELETAL DEVELOPMENT Skeletal piece of hyaline cartilage Grows by internal expansion and from the surface Cell enlargement/hypertrophy Matrix calcification Calcified cartilage can be resorbed like bone, and be attached to bone selective erosion into mineralized cartilage EARLY ENDOCHONDRAL OSSIFICATION perichondrium periosteum Bony collar provides support as mineralized cartilage is eaten away } EPIPHYSIS } DIAPHYSIS/SHAFT primary ossification front EARLY ENDOCHONDRAL OSSIFICATION: Cell activities Expansive/interstitial growth by cartilage cell division and matrix synthesis Hypertrophy of chondrocytes precedes calcification Bony collar Chondroclasts & other cells eating into calcified cartilage Bone laid down as a seam on remnants of calcified cartilage by Marrow osteoblasts primary ossification front MIDDLE ENDOCHONDRAL OSSIFICATION Secondary ossification centers start by repeating the processes of the 1o center Bone would be larger than in the previous } EPIPHYSIS } SHAFT primary ossification front LATER ENDOCHONDRAL OSSIFICATION Articular cartilage Growth/epiphyseal plate Secondary ossification centers - + Shaft bone grows by deposition on the outside, with mild resorption on the inside surface, plus osteonal remodelling in the interior Bone would be larger than in the previous view No surface growth possible on loaded surface STRATEGIES FOR GROWTH WITH USE Articular cartilage Secondary ossification center Interstitial growth to elongate bone here Erosion matching cartilage’s expansive growth keeps plate same width Other growth plate doubles the ability to grow in length Growth/epiphyseal plate - + Shaft bone grows in width by deposition on the outside, & mild resorption on the inside surface, with osteonal remodelling in the interior Separation of function: articular cartilage is just for load-bearing ZONES/LAYERS OF THE GROWTH PLATE }RESTING } PROLIFERATION Expansion } HYPERYTROPHY } Matching erosion Osteoclasts stop the trabeculae from forever extending CALCIFICATION } OSSIFICATION new bone on calcified cartilage Cartilage is replaced by bone. There is no transformation of cartilage into bone RICKETS - Expression in growth plate Normal Vitamin D & Ca2+ deficiencies Cartilage cannot mineralize CARTILAGE LENGTHENS & IS WEAK V. little erosion & bone substitution WHERE AM I? Online Anatomy Module 1 ORIENTATION You are at the End CELL EPITHELIUM Caution how you exit. BACK on your BONE browser is needed MUSCLE Unfortunately there is NERVOUS SYSTEM no way that you can directly reach other AXIAL SKELETON topics listed here by APPENDICULAR SKELETON clicking on them. You get there by going back MUSCLES to the Paramedical Anatomy menu EMBRYOLOGY