Skeletal System Notes PDF

Chapter 6 Skeletal System The skeletal system contains bones as well as ligaments, cartilage, and other tissues that connect bones Is divide into the: ◦ Axial skeleton: forms long axis (80 Bones) in red...

Chapter 6 Skeletal System The skeletal system contains bones as well as ligaments, cartilage, and other tissues that connect bones Is divide into the: ◦ Axial skeleton: forms long axis (80 Bones) in red SIDED ◦ Appendicular skeleton: bones of the limbs and gridles (126 bones) shown in yellow 3ineachear Functions of the skeletal system support 00 0 Storage of minerals and lipids: Ca++ salts and PO4 ions Blood cell production : RBCs and WBCs are produced in red marrow Protection: of soft organs; eg. Ribs protect the heart and lungs, skull protect brain, vertebrate shield spinal cord, pelvis cradles digestive and reproductive organs Leverage: change in magnitude and force is generated bu muscles to provide movement Storage of Fat (energy): in yellow bone marrow Classification of Bone according to 6 shapes: Long bone - humerus (arm bone) ◦ They have the hollow structure where hollow exist. ◦ Makes the bone lighter ◦ Fibula, radius, ulna, tibula, metatarsals, phalanges o Flat bones - pareital bones, sternum, ribs, parietal (cranial bones) ◦ Flat in appearance and lacks neural cavity ◦ Scapula, parietal bone Sutures bones - unique to each person so ◦ Different sizes, jigsaw puzzles Irregular bones - irregular shapes, 26 vertebras are examples ◦ Some skull bones are weird shape Sesamoid bone - sesame shapes, patella or knee bone ◦ Found inside tendons located near joints at knees and in hands and feet. 5 Short bones - carpal bones, tarsal bones ◦ Rectangular and squarish Blood vessels are very fragile thats why they are not seen in tendons and ligaments Structure of Bone Elevations and etc. = are there where tendons and ligaments are attached too of Tunnels and grooves are for blood vessels and nerves to enter the bone Diploe = two folds of compact bone Two layers: A 1. Compact (dense) 80% of the body- thin layer (cortical bone) A. Very hard B. surrounds spongy bone of epiphysis; C. Also found along diaphysis surround medullary (marrow) cavity core 2. Spongy (20%) - cancellous/trabecular bone/trabeculae A. Filled with bone marrow B. Trabeculaer comes from the word branching C. They are avascular Short Irregular Flat Flat bone has similar structure (no medullary cavity) for bones such as: Short bone = carpal bone Irregular = vertebrae Flat The bone is surrounded by periosteum = peri = surrounds entire bone. Why do we have spongy bone? spongy bone and medullary cavity, reduce the weight of bone, hand if you are a bird and want to flight. reduces the amount of muscle to required to move Provides space for red and yellow marrow Epiphysis = distal and proximal Metaphysis = neck region spongybone both epiphysis and metaphysis is spongy D O bone, they are coloured red to indicate that there is red bone marrow. Compact bone = running the perimeter of the bone Epiphyseal line = growth plate of the bone, where the bone grows to make it longer. Endosteum = Inner lining of the bone, innerlinnings lines the medullary cavity Bones are highly vascularized When bones are broken it will bleed. Periosteum = lines the diaphysis, where it linestheouter lines the entire bone except the very end. Articulate cartilage is hyaline. the from Further trunk Compact Bone Structural Unit: Osteon Concentric lamellae pink cells = cells are CT spread apart Beige = matrix The cells are arrange in concentric layers, the matrix is arranged in layers. Surrounds the concentric canals and allow nutrient and O2 to diffuse Concentric canals blood vessels and nerves are penetrating these cells are trapped; they are needed to provide nutrients to the cells Interstitial lameliae = inbetween layers Circumferential lamellae = surrounds the entire diaphysis Lots of collagen fibers (matrix) they give a lot of strength to the bone, concrete cna break easily (Ca++), collagen acts like steel that will enable the bone to withstand pressure. bone is supportive connecting tissue Only 2% of the bone is cells Endosteum lining each central canal Histology of Bone Matrix CaioPoy OH mineral component - CaPO4 binds to calcium hydroxide to make -> crystals of hyroxyapatite: Ca10(PO4)6(OH)2 (inorganic matrix); makes up most of the bone. ◦ Plus Na, Mg, and F mineralcrystal Mineral crystals are hard and brittle = 55% 55 collagen 1/3 weight of bone = collagen 30% ◦ Collagen in stronger than steel and flexible 30 0 organic ‣ Part of osteoid = organic matrix of the bone 15 Water ◦ Does spongy bone have osteons? = no! No central canal, no blood vessels coming in Water 15% Organic components cells (2%) and osteoid = 90% protein (collagen) and 10% sugar compound Orientation of trabeculae (spongy bones) withstands forces (stress from manual directions) Photo: Does spongy bones have osteons? No! trabeculae = spongy bone 18 netiffuse allows ◦ If we cut this to see what it looks like ◦ The reddish cells are separated by calcium phosphate collagen matrix ◦ Different than osteons, not considered as osteons ◦ Osteocyte = red, mature bone cells ◦ Osteoblast ◦ Osteoclast O ◦ Canaliculi = diffusion of nutrients to keep cells alive Orientation of trabeculae: withstands forces from many directions, they are designed that way. Experiment: if you take out the organic matrix of the bone ◦ This includes the cells and the osteoids ◦ Lots of proteins (mostly collagen) ◦ This is what gives its receilency, it will shatter instantly If you remove the inorganic layer, Ca10(PO4)6(OH)2 ◦ Removing the hard brittle matrix ◦ The bone will then just contain collagen making it flexible! *Femure is the largest bone = can withstand ten to fifteen times your bone weight ◦ Directed by the structures of the trabeculae ◦ As well as the cortical bones, that has osteons which are all lined up in longuitudinal fashion that will help held the weight of the body. ‣ Same as grabbing a bundle of straws = it will be hard to bend them. ‣ That’s why most bones break in the transverse axis Bone Cell Types 4Types 1. Osteoprogenitor cells (osteogenic cells) arise from osteo = bone; genic = genesis, creation of They are the stem cells for the bones They are capable of dividing, their daughter cells will be osteoblasts They are part of mesenchymal stem cells = Mulitpotent stromatolites (CT) cells o Located in periosteum and endosteum Function to divide and produce osteoblast Important in maintenance and repairing fractures B is for building = OsteoBlast osteocytes is mature osteoblasts = blast are also used for immature cells Mesenchymal stem cells Produce cells that differentiate into many different lineage Osteoprogenitor cells give rises into immature osteoblasts, which then give rises to mature osteocytes. they are multi potent cells they can form cells that differentiate into many things Give rise to many different lineages 2. Osteocytes mature bone cells o They are now surrounded by ECM, and lives in a lacunae of bone they are mechanosensors = it senses when bones are under pressure 1. Secrete osteoid (collagen / sugar protein) -> control mineral deposition of calcium phosphate -> build bone! When stressed (e.i bearing weight) 2. Secrete acid phosphatase -> dissolve bone! Also when repairing micro-Fractures! After which it will put new osteoid Functions A. Bone turnover - maintaining protein and mineral content regulate bone density by releasing chemicals that inhibit osteoclasts and ostimulates osteoblasts (building activity) B. Bone repair if exposed by a break, osteocytes are thought to release chemicals taht stimulate bone formation by stimulating osteoblasts. 3. Osteoblasts immature bone cells Location: periosteum, makes the bone wider and also for repair Bone builders Secret the organic component of matrix ◦ osteoid osteolysis need Cattso ◦ Regulation of calcium and phosphate concentrations in body fluids We destroyour weuse bones Microscopic Structure of Bone the diaphysis is wrapped in a connective tissue called the periosteum ◦ This contains rich nervous and blood and lymphatic supply ◦ Houses many osteocytes (cause there is a lot of vessels) ◦ They have perforating fibers that provides a means for tendons and ligaments. The compact bone receives this rich blood supply through the Haversian system (i.e osteon) Periosteum consists of 2 Layers 1. Fibrous outer layer dense irregular CT connectivetissue Fibroblasts and collagen fibers that extend from periosteum into bones ◦ Sharpey’s fibers 2. Inner cellular layer I filled with cell types: fibroblasts and osteoprogenitors, osteoblasts Functions of periosteum 1. Provides isolation of bone from surrounding tissue 8 2. Provides a route for circulation and nervous supply 3. Participates in bone growth and repair 8 4. Interwoven with tendons and ligaments Endosteum incomplete cellular layer Cells ◦ Osteoprogenitors ◦ Osteoblasts ◦ Osteoclasts They dont contain osteocytes because they are mature and looked in lacunae Function bone growth, repair, and remodelling Bone Development Osteogenesis bone formation A life long process In embryo ◦ Endochondral ossification ‣ Within cartilage there is ossification ‣ The cartilage was turned into bone ◦ Intramembranous ossification ‣ Within the membranes of your tissues becomes bones Childhood ◦ Interstitial growth (growth in bone length ) ◦ Appositional growth (growth in bone width) Adult ◦ They are still alive and they turne over every 5-7 years ◦ Bone remodelling Formation of the Bony Skeleton Embryonic skeleton by week eight, skeleton formed of hyaline cartilage which will be replaced by bone All the yellow is cartilage Twelve week old fetus. The red areas represent bones that are forming (calcified). Translucent areas represent cartilage (uncalcified) This is the endochondral ossification 1. Intramembranous ossification dermalbones when osteoblasts differentiate with a mesenchymal or fibrous CT osteoblast osteoids mineralize Bones formed this way are called dermal bones ◦ They are formed in the middle of dermis tissue ◦ Flat bones of the skull, mandible (lower jaw) and clavicle CazP04 Blood deposit nature of original support structure: spicules ◦ Small struts of developing bone that trap osteoblasts in place (in lucunea) Mesenchymal cells cluster and differentiate first into osteogenic cells and then into osteoblast = building, they are building ECM ◦ they secrete osteoid, which becomes mineralized as osteoblast take minerals 00 Ca3(PO4)2 from the blood and deposit ◦ 90% collagen + 10% sugar compound 1 A ◦ (1) This is called the development of ossification center: osteoblast secret organic extracellular matrix = once there is enough ECM they will lock themselves into a lacunae ‣ This will keep expanding there will be osteoblast surrounding the perimeter ‣ They will keep on building bone ◦ The bone then start expanding into a series of spicules spread in top surrounding tissue ◦ (2) calcification : Ca++ and other minerals salts are deposited and ECM calcifies ‣ Bone expands as bony spicules that grow together, trapping blood vessels within the bone. ‣ Spicules form trabeculae which then form spongy bone ‣ Some spongy bone is remodeled to be compact, while the inside is spongy ◦ The connective tissue around the outside forms the fibrous layer of the periosteum 2. Endochondral ossification most bones are born like this Osteoblasts replace chondrocytes (which have died) Nature of the original support structure: hyaline cartilage model  perichordium osteoblast Endochondral Ossification Step 1 size eases as the cartilage enlarges, chondrocytes near the center of the shaft in teaser greately in O air O perichond The matrix is reduced to a series of struts that soon begin to calcify ium hollow The enlarged chondrocytes then die and disintegrate, leaving cavities within the cartilage We are making hyaline artilage, the ones on the middle is old and starts dying C Bloodvessels Step 2 blood vessels grow around the edges of the cartilage, and the edges of the cartilage, The cells of the perichondrium converts to osteoblasts. The shaft of the cartilage then becomes ends heated in the superficial layer of the bone Theated covered Step 3 the blood vessels penetrate the cartilage Osteoblast starts producing spongy bone at the primary ossification centre Step 4 remodelling occurs as growth continues, creating a marrow cavity. The bone of the shaft become thicker and further growth increases length and diameter. Osteoclasts they break down trabeculae forming medullary cavity cartilageleft Osteoblast continue to add bone at ends of the cavity Step 5 capillaries and osteoblasts migrate into epiphyses This creates secondary ossification Centers Step 6 soon the epiphyses are filled with spongy bone. An articulate cartilage remains exposed to the joint cavity; over time it will be reduced to a thin superficial layer At each metaphysis, an epiphyseal cartilage separates the epiphysis from diaphysis state of most bones at birth Postnatal growth of bones Growth in length chondrocytes (cartilage cells) in the epiphyseal plate continue to divide and grow, adding length to them bone. ◦ Chondrocytes closets to the cavity dies Osteoblasts (builders) ◦ Migrate towards epiphysis replacing cartilage with bone Bone developers from hyaline cartilage, which becomes fully ossified after birth: ◦ Calcilfication ◦ Deterioration of chondrocytes (die), leave cavities ◦ Replacing with osteoid tissue (osteoblast and clast) Bone growth is under hormonal control during development, bone grows longitudinally through the formation of new cartilage through the epiphyseal plate, this process is complete after puberty. Lateral bone growth is achieved by osteoblasts in the periosteum laying down new bone Osteoclast in the medullary cavity breaking down old bone Summary 1. Development if cartilage model: mesenchymal cells develop into chiondroblastss, which forms the cartilage model 2. Chondrocytes produce a substance that inhibits the formation of blood vessels limiting O2 and nutrient delivery 0 3. Chondrocytes in shafts enlarge and eventually die p 4. Chondrocytes in the primary ossification site enlarge and stop secreting collagen and 0111 other proteoglycans sand begin secreting alkaline phosphatase an enzyme required for mineral deposition. 5. Calcification of the matrix occurs 6. Blood vessels grow into perichondrium transforming it into periosteum containing Osteoprogenitor cells which become osteoblasts 7. Osteoblasts secrete osteoid and create bone collar against shaft of cartilage model -> generate collar of bone o 8. Mature chondrocytes can not divide and die leaving cavities 9. Osteoblasts in ossification sites produce osteoid and turn into osteocytes as mineral deposits surround and harden around them How are new osteons and central canals formed during appositional growth? (Width-wise growth) 1. Ridges in periosteum create groove for periosteum blood vessel O 2. Periosteum ridges fuse, forming an endosteum-lined tunnel they have osteoblastwiththem 0 3. Osteoblasts in endosteum build new concentric lamellae inward toward center of tunnel, forming a new osteon Gets 4. Bone growns outwards as osteoblasts in periosteum build new circumferential lamellae. Osteon formation repeats as new periostea’s ridges fold over blood vessels Ben Enlargement of medullary cavity with increased Brien diameter resulting from appositional growth increase the diameter of the long bone, forms new circumferential lamellae Involved both osteoblast and osteoclasts Growth in width by appositional growth where you have osteoblast in periosteum ◦ Osteoblast under the periosteum lay down bone Osteoclast break down bone on inside of medullary cavity ◦ Bone increases in diameter, cavity enlarges ◦ In the midddle, starts dissolving bone to extend diameter At Puberty 000 under influence of sex hormones, growth hormine, thyroid hormone Cartilage in epiphyseal plate is reaplaced with bone -> No further growth in length Bone remodeling O O bone remodeling occurs through life and involves resorption of old bone and deposition of new bone where it is needed Remodeling occurs in response to ◦ Bone growth (to maintain proper thickness and shape) ◦ Blood Ca++ levels (storage) ◦ Mechanical stress on the bone Why do sharks have a skeleton made of cartilage instead of bone? weight is reduce -> saves on energy Blood Supply to the bone Nerve Supply periosteum Endosteum And the bone itself is richly supplied with sensory nerve endings Hormonal and Nutritional Requirements for Normal Bone growth Hormonal 1. Growth Hormone from the pituitary gland ( at the epiphyseal layers) , promotes osteoblast activity 2. Thyroid hormone thyroxine ( at the epiphyseal layer) Stimulates cell metabolism, promotes osteoblast activity 3. Calcitriol produced by kidneys; derived form vitamin D3 o Allows normal absorption of Ca++ and PO4 ion from the digestive tract 4. Sex hormones estrogen and testosterone Promote growth, cause osteoblasts to produce bone faster When production fo sex hormones increase at puberty, epiphyseal plates become narrower Nutritional Requirements for bone growth 1. Calcium and phosphate salts to prevent rickets (children) and osteomalacia (adults) 2. Vitamin C required for collagen synthesis Stimulates osteoblast differentiation 3. Vitamin A E stimulates osteoblast activity 4. Vitamin K and B12 required for synthesis of proteins in normal bone = large in collagen Regulation of Bone Remodeling Hormonal maintain a clacium ion in blood and interstitial fluid at 9-11 mg/100 ml blood Two organs monitor calcium levels ◦ Para (beside)thyroid glands ‣ Releases parathyroid hormone in response to lower than normal Ca++ in blood ‣ Effects (cannot inhibit calcitonin secretion) Stimulates osteoclast activity ◦ Disssolve calcium ion off the bone, which will go into the blood and help the levels go up Increase the rate of absorption of Ca++ from intestine Decrease the rate of excretion by kidney (don’t pee too much) ◦ thyroid glands ‣ Release the hormone calcitonin ‣ In response to highe than normal Ca++ in blood Inhibit tha activity of osteoclast Increase rate of kidneys excretion Ca++ Bone remodelling: response to mechanical stress Wolff’s law: bones are remodelled in response to forces placed on them How does it work stress generates electrical currents in bone Osteocytes are mechanosensors and secrete chemicals that alter the activities of osteoblasts and osteoclasts (make bone more dense and thicker) Net effect of Wolff’s law bones that are used to stressed become stronger ◦ The trabeculae is shaped to cope with stress Unstressed bones are remodelled to become weaker When stress is applied to the bone, the minerals in the bone produce a weak electrical field that attract osteoblast. -> result in the bone make thicker Repair of Fractures Treatments realign bone pieces = reduction of movement (i.e immobilize) Open (compound ) = term for fracture in which the broken bone breaks through the skin o