hey everyone's dr. mark on this is chapter six on bones and skeletal tissues so before we get into bones we want to talk about cartilage and we covered cartilage in the first unit of lab we know that cartilage is found throughout the adult body we can see cartilage in the external ear and we know the different types of cartilage so the carlesha found in the external ear is elastic cartilage we know there's cartilage of the nose the articular cartilages and the costal cartilage as well as the cartilages in the larynx and the trachea and we saw cartilage in the intervertebral discs the pubic symphysis and articular discs so this figure shows you the types of cartilage that we have covered and where they are located in the body we have three types of cartilages we have Highland cartilage elastic cartilage and fibrocartilage and what's nice about this picture is that it's color-coded so you can see where the different types of cartilage are found throughout the body and we covered in lab we have elastic cartilage in the external ear the pinna I can't really see the epiglottis but then we have and blue the hyaline cartilages that we see in the nose the costal cartilages the small bronchi in the lungs as well as the trachea and the larynx and then we have my fibrocartilage --is found in the intervertebral discs as well as the articular cartilages and the joints specifically in the knees and the Menace kisses I'm in the sky so just some general characteristics of cartilage we have this structure called the perichondrium the perichondrium surrounds cartilages it helps resist outward pressure and helps function in growth and repair of cartilage it consists primarily of water and is a very resilient tissue it actually has this characteristics where it springs back it's original shape now all cartilages share some similar properties we know that the mature cell type is called the chondrocyte so anything with this root word Kandra is talking about cartilage so chondrocyte is a cartilage cell in this case it is the mature cartilage cell and we know the chondrocytes are located in spaces called lacunae so they're located within lacunae we know that because it's a type of connective tissue it has an extracellular matrix and we know the matrix contains fibers as well as the jelly-like ground substance and we know that the chondroblasts is the cell that helps produce the different types of fibers as well as the ground substance of the extracellular matrix the first type of hyaline cartilage that we've covered is Highland cartilage hyaline cartilage is the most abundant cartilage here we see that the chondrocytes do appear spherical collagen fibers so the collagen unit sidewall is the only type of fiber that is found in the matrix of Highland cartilage and we know that the ground substance actually holds a large amount of water which provides support through flexibility the second type of cartilage we have is elastic cartilage that contains many elastic fibers it is because of these fibers that is able to tolerate repeated bending and we can see elastic cartilage again in the epiglottis as well as the external ear in the peanut of the ear the third type of cartilage that we covered was fibrocartilage fibrocartilage actually resists strong compression and strong tension it's an intermediate between Highland and elastic cartilage and we can see fibrocartilage in the pubic symphysis again that cars that connects the two hip bones the ox coxae anteriorly you can also find fibro college in the meniscus as well as the annulus fibrosus in the intervertebral discs and in lap we saw histo preparations of the different types of cartilage we saw hyaline cartilage which had a ground-glass appearance you can see the chondrocytes in there lacunae we saw elastic cartilage with those lovely elastic fibers between the chondrocytes in there leepu day was very darkly stained and then we saw fibrocartilage fibrocartilage the chondrocytes are kind of in rows and you can see these lovely collagen fibers within the matrix so how does cartilage grow there are different types of growth within cartilage you have a positional growth this is when you have the chondroblasts in the surrounding perichondrium that will actually produce new cartilage and then you have interstitial growth the chondrocytes within the cartilage will divide and secrete new matrix now Carter stops growing when the adult skeleton stops growing so moving on to bones bones actually contains several types of tissues they are dominated by of course bone connective tissue also they contain nervous tissue as well as blood connective tissue they contain cartilage in the articular cartilages where the bones articulate with one another they also contain epithelial tissue that lines the blood vessels so there are different types of tissues that make up bone of course we have functions of bones functions abodes include supports bones provide a hard framework for the body movement skeletal muscles will use the bones as levers protection provide protection of underlying organs they are also also a site for mineral storage they are reservoir for important minerals also within bones we have blood cell formation hematopoiesis black bone contains red bone marrow where we have formation of new blood cells also bones participate in energy metabolism we have the osteoblasts that secrete osteocalcin osteocalcin is a hormone that stimulates pancreatic secretions that reduce blood sugar levels or through insulin osteocalcin also influences fat cells causing them to store last fat and to secrete a hormone that increases the insulin sensitivity of cells so these results will have clinical implications for the treatment of metabolic disorders that are related to blood sugar regulation such as type 2 diabetes so talking about bone tissue bone tissue has both organic and inorganic components the organic components of bone tissue include cells fibers and ground substance the inorganic home components include mineral salts that do invade the bony matrix the extracellular matrix of bone has a unique composition it gives the bone exceptional properties we know that the extracellular matrix about 35% of it is made up of organic components that help contribute to the flexibility and tensile strength of bone mm-hmm 65% of the extracellular matrix is made up of inorganic components that help provide hardness exceptional hardness and help with resistance of compressive forces the there are cells that make up bone so there are three types of cells in bone that produce or maintain bone we have osteogenic cells osteogenic cells are based stem cells that will eventually differentiate into osteoblasts again we see the word blast think immature cell however osteoblasts will actively produce and secrete bone matrix and bone matrix is osteoid osteoid is just a fancy term that means bone like so the bone matrix that is secreted by the osteoblasts is osteoid or bone like the third type of cells are the mature cells these are the osteocytes these cells help keep the bone matrix healthy we also have osteoclasts osteoclasts are found within bone tissue osteoclasts are responsible for resorption of bone meaning the breakdown of bone we want bone to be broken down in times when we need certain certain molecules if we're for example low on calcium or phosphorus osteoclasts actually break down bone to give our body a supply of these these minerals these molecules osteoclasts are derived from a line of white blood cells they secrete hydrochloric acid as well as lysosomal enzymes to help break down bone now osteoblasts build up bone whereas osteo class break down bone and usually these two kind of even each other out because you don't want one more than the other so if osteoclasts are breaking down bone we have osteoblasts that help build up bone so we can classify bones according to shape we have long bones long bones are longer than they are wide these bones have a shaft plus ends to the shaft there are short bones these are roughly cube shaped we have flat bones that are thin and flattened and usually curved and we have irregular bones base those that fall into the other that don't fit into the other categories so irregular bones are of various shapes and do not fit into these other categories here we just see examples of the different classifications of bones so for example a long bone that has a shaft plus the two ends example this is the humerus a short bone an example this is one of the bones in the foot or ankle this is the talus and then we have flat bones example this is the sternum in the thoracic cage and then we have irregular bones that are irregularly shaped example this are the vertebrae within the spinal column so we want to go over the gross anatomy bones bones are made up of compact bone compact bone is a dense outer layer of bone and then they are also made up of spongy or cancellous bone this is the internal network of bone we see structures culture Bakula Rebecca there are these little beams of bone if you actually kind of open up well you can see little beams with little spaces inside so open spaces between the trabeculae are filled with bone marrow and bone marrows importance and has some very important characteristics so a typical structure of a long bone it has these structures we has the diaphysis the diaphysis is the long shaft of a bone we have the epiphysis these are the ends of a bone with in a typical long bone of course we have blood vessels because bone is very well vascularized it does need a blood supply within the bone is the medullary cavity this is a hollow cavity filled with yellow marrow and then we have the membranes within a typical long bone we have the periosteum the periosteum is a connective tissue membrane that covers the entire outer surface of each except on the ends of the epiphysis where articular cartilage occurs we have perforating collagen fiber bundles called sharpey's fibres again these are thick bundles of collagen that will run from the periosteum into the bone matrix and we have the end ostium the end ostium is the internal bone surface our covering made up of a connective tissue so here we see the structure of a typical long bone again we have this long shaft which is the diathesis we have the two ends we have the proximal epiphysis and the distal epiphysis within the the bone we have a medullary cavity and then the outer connective tissue lining is the periosteum and then we have the internal and ostium that lines the medullary cavity and then within the medullary cavity there is yellow bone marrow and then we can see the two types bone we have a compact bone which is the outer covering and then we have the spongy bone within made up of these trabeculae or beams with spaces and within the spaces we have yellow marrow yellow bone marrow so um short irregular and flat bones also have a similar structure flat bones short bones and irregular bones contain bone marrow but don't have a marrow cavity like long bones do within these bones we have structures called deploy a deploy are the internal spongy bone of flat bones and here we see that spongy diplo way and then the outer compact bone again we have those structures that your Bakula that are like little beams and then spaces within the trabeculae so bone design and stress we note the anatomy of a bone will reflect the stresses that the bone comes in contact with we know that compression and tension are greatest at the external surfaces so here we see a figure of the bone anatomy and bending stress so we can see that body weight is transmitted through this is actually the femur but body weight is transmitted through the head of the femur which will threaten to bend the bone along this arc this dotted line right here so the strongest forces occur at the periphery of this long bone so we have two types of forces we have compression forces on this loaded side you can see that these forces compress the bone and then we have tension forces on the opposite surface so these forces are resisted by the outer compact bone and then we'll have actually a cancelling out so tension and compression will cancel each other out internally at the point of no stress as a much as a result much less bone material will be needed internally than superficially okay and this is just diagram of the stress the different types of stress trajectories through the proximal femur during loading and again these forces will cancel each other out of the point of no stress and compression lines are shown in red where as the tension lens are shown in blue and we can see these lines and we can see we compare this figure with the actual picture of the procs the inside of the proximal femur where the trabeculae kind of aligned with these forces these stress forces so much the last material is needed in this area of the bone because we know that's due to the structure of the bone the compression forces and the tension forces will cancel each other out so we talked a little bit about bone markings and the other day bone markings are just superficial surfaces of bones that will reflect the stresses on them there are three broad categories of goal and markings that you guys need to know bone markings provide projections for muscle attachments secondly and they are they provide surfaces that will form joints they can also be depressions and openings so this Table six point one is actually a really good table that you guys should study because it shows the three categories of bone markings and the different bone markings within those categories so make sure you know which bone markings are in which categories so the first category for bone markings are projections that are sites of muscle and ligament attachments so we have structures called tuberosities tuberosities are large rounded projections they may be roughened we have structures called crests so for example here the iliac crest right here the crest is a narrow ridge of bone that is usually prominent we have trochanter zandig Andrew Cantor's are very large blunt irregularly shaped processes that occur only on the femur so we have the greater trochanter and the lesser trochanter and then we have a line that kind of connects them so a line is a narrow Ridge of bone that is less prominent than a crest so for example the intertrochanteric line can see is definitely a lot smaller or less prominent than a crest and this line connects the greater trochanter would be less search or cancer but lines are found throughout others other bones in the body a tubercle is just a small rounded projection or process we have an epicondyle which is a raised area on or above a condyle when we talk about muscles will later talk about the medial epicondyle of the humerus and how all the flexor muscles within the forum can attach to the medial epicondyle of the humerus a spine is just a sharp slender often pointed projection and a process is just any bony prominence we have bone markings that have surfaces that form joints for example on the rib we have the head the head is a bony expansion carried on a narrow neck we also have facets facets are smooth nearly flat articular surfaces that articulate with other bones and then we have a contact a condyle is just a rounded articular projection which often articulates with a corresponding fossa of another bone and this again helps form and articulation with another bone then we have depressions and openings usually these openings or depressions are for passage of vessels and nerves so the first opening we'll talk about as a form and foramen is just a round or oval opening through a bone the plural for foramen is foramina we have grooves that are furrows where vessels can also travel along then we have fissures fissures are narrow slit like openings notches are indentations at the edge of the structure and then we have other bony markings that fall in this category we have fossa these are shallow base and like depressions in a bone that often serve as an articular surface or where you know muscles can can sit such as the subscapular fossa and then we have a me itis of me this is just a canal like passageway sinusitis is a cavity within a bone filled with air and lined with mucous membranes the sinuses that we'll be talking about are the paranasal sinuses within the skull so here we see a figure of the microscopic structure of compact bone this is a section from the diathesis of a long bone and we can see the different structures that make up the compact bones so under the mr. slides we saw the osteon which is this rounded structure within the bone tissue and then we saw those lines as well as the osteocytes in the lacunae we saw those thin spidery like lines called canaliculi which allow for communication between the osteocytes and we saw these concentric lines within the osteon called lamellae and then in the middle is the central canal where we have passage of nerves as well as blood vessels and we'll talk more about these structures so compact bone is the structure that makes up the outer part of the bone compact bone contains passageways for blood vessels lymph vessels and nerves within compact bone we have these rounded structures called osteons osteons are also called haversian systems osteons are long cylindrical structures that are or parallel to the long axis of the bone and to the main compression stresses functionally they are basically major weight-bearing pillars within compact bone osteons function and supports and structurally they resemble rings of a tree and cross-section we saw those concentric layers within the osteon so the osteon contains structures called lamellae each of the tubes within the osteon is a lamellae which is a layer of bone matrix in which collagen fibers and mineral crystals will align and run in a single direction and then each layer of lamellae alternates directions to kind of help with the twisting forces so osteons also contain a central canal central canal runs through the core of each osteon and also is called a haversian canal it's lined with endosteum and contains its own blood vessels and nerve fibers but going back to the lamellae the fibers and crystals of adjacent lamellae always run in opposite directions this alternating pattern is optimal for helping to withstand torsion or twisting forces and then we have a centralized central canal we also have perforating canals perfect these perforating canals are known as bulk mince canals these perforating fans will lie at right angles to the central canal and connect the blood and nerve supply of the periosteum to the central canals and marrow cavity then we have canaliculi which we talked about canaliculi are thin tubes also known as little canals that run through the matrix and connect neighboring lacunae to one another and to the nearest capillaries such as those in the central canal these canaliculi allow for communication between osteocytes and they form gap junctions between osteocytes so here we see the structures within the osteon or havisham system we have that central canal that allow for passageway of blood vessels and nerves then we have the outer lamellae again these lamellae are concent concentric structures that will run parallel so if the inner lamellae for example is going a clockwise direction the van lay on top of that will go in a counter clockwise position so the collagen fibers will run in different directions to help kind of help with the twisting forces that occur on the bone so these are the structures that make up compact bone spongy bone is less complex than compact bone we have those beam like structures cultured Bekele that will contain layers of lammle and osteocytes however they spongy bone and the tareq they are too small to contain osteons so you don't have those have ershon systems and be spongy bone in here again we see those beam like structures of the trabeculae and then the spaces within the trabeculae so we have a layer of and ostium again they contain osteoblasts that are important for forming new bone and forming matrix and then we have the mature osteocytes within the solid portions of the trabeculae so how does bone develop we have the process of ossification also known as osteogenesis which is bone tissue formation membrane bones are formed directly from Mezen kind and they ossify through what's known as interim membranous ossification so membranous bones form directly from Mezen kind without first being modeled in cartilage all bones to the skull except for a few at the base of the skull are of this category the clavicles are the only bones formed by intramembranous ossification that are not in the skull other bones will develop from a cartilage model so developed initially from Highland cartilage and this is known as endochondral ossification so all bones from the base of the skull down except for the clavicles are endochondral bones meaning they are first modelled in Highland cartilage which is then gradually replaced by bone tissue so again this is known as endochondral ossification so here we see intramembranous ossification again these are the bones of the skull except for the bones the base let's call and the clavicles so this occurs in the developing fetus we first have ossification centers that will appear in the fibrous connective tissue membrane so we'll have selected centrally located mesenchymal cells that will eventually cluster and differentiate into osteoblasts and form an ossification Center okay so we have our osteoblasts kind of coming together forming this ossification center so we know that osteoblasts secrete bone matrix which is osteoid so secreted within the fibrous membrane which will eventually calcify so osteoblasts begins to secrete osteoid which is then calcified within a few days trapped osteoblasts eventually will mature to become osteocytes so here we see newly calcified bone matrix so calcification basically is just the hardening of the matrix to come bone then woven bone and periosteum will form accumulating osteoid being secreted by the osteoblasts laid down between embryonic blood vessels in a random manner which will results of a network of trabeculae instead of lammle and this is called woven bone vascularized mesenchyme will condense on the external face of the woven bone and we become that outer periosteum again periosteum being that outer connective tissue membrane that will cover the entire outer surface except for any bends that might articulate so lamellar bone will then replace woven bone just deep to the periosteum and we have a red marrow that appears trabeculae just deep to the periosteum will thicken and will later be replaced with mature lamellar bone forming compact bone plates spongy bone also known as deploy will consist of distinct trabeculae which will persist internally and then it's vascular tissue becomes red marrow so then we also have endochondral ossification this includes all bones basically from the base of the skull except for the actual Bulge of the skull and the clavicles basically these bones are modeled in highland cartilage so are formed from highland cartilage this begins forming late in the second month of embryonic development and will continue forming until early adulthood a year we see the steps of the endochondral ossification of a long bone so first we have the formation of a bone collar so the bone collar will form around the diaphysis of the hyaline cartilage model then we have the cartilage in the center of the diaphysis will calcify and then develop cavities here we see areas of deteriorating cartilage matrix then we have the periosteal bud which will invade the internal cavities and formation of spongy bone beginning to form then this occurs about the third month of fetal life and then at Birth the diaphysis will elongate elongation of the shaft and a medullary cavity will form as ossification continues will then have secondary ossification centers that will appear in the epiphysis of the the different ends of the the long bone and then the epiphysis will ossify when completed hyaline cartilage remains only in the epiphyseal plates here as well as the articular cartilages so we want to talk about the anatomy of the epiphysial growth areas and epiphysial plates of growing bones cartilage is organized for quick efficient growth CARTER cells will form tall stacks the chondroblasts at the top of these stacks will divide very quickly the epiphysial plates will push the epiphysis away from the diathesis and then we have lengthening of the entire long bone older chondrocytes will signal surrounding matrix to calcify and then or older chondrocytes will die and disintegrates which will leave long trabeculae or beams or spicules of calcified cartilage on the diaphysis side trabeculae are partly eroded by osteo class again these cells that help break down bone they have the hydrochloric acid and the enzymes that help with breaking down a bone osteoblasts will then then cover trabeculae with bone tissue so they help with putting down bone or forming bone tissue trabeculae will then filing be eaten away from the tips by osteo class you have this kind of breaking down and building up a bone by the two different cells so osteoclasts kind of break down bone whereas osteoblasts versus Abby and osteoblasts build up bone so here we see an organization of these cells and cartilage cells within the epiphysial plate of growing long bone so we have the resting zone within the epiphysial plate and then we have the Pearl iteration zone this is where we have cartilage cells undergoing mitosis or cell division we have the hypertrophic zone this is where we have enlargement of the older cartilage cells then we have the calcification zone this is where a matrix becomes calcified cartilage cells will die and the matrix begins deteriorating and here we see the ossification zone ossificans the ossification zone is where we have a new bone formation so after birth we have Co sale growth of endochondral bones so during childhood and adolescence bones will lengthen entirely by growth of the epiphyseal plates cartilage is replaced with bone connective tissue as quickly as it grows and the epiphysial plate will maintain a constant thickness and the whole bone will lengthen as adolescence draws to an end Kadri bust will divide less often the epiphyseal plates become thinner cards which means the cars will stop growing and is replaced by bone tissue so long bones will stop lengthening when the diaphysis and the epiphysis fuse growing bones will widen as they lengthen again we have these cells the osteoblasts will add bone tissue to the external surface of the diaphysis whereas the osteoclasts will remove bone from the internal surface of the diathesis and now we have what's known as a positional growth acquisition growth is the growth of a bone by addition of bone tissue to its surface bone growth is regulated through hormones and you have different hormones that are included so we have the growth hormone which is produced by the pituitary gland specifically the anterior pituitary gland growth hormone will stimulate bone growth by stimulating the epiphysial plates we have thyroid hormone secreted by the thyroid gland that ensures that the smells and retains proper proportions and then we have sex hormones such as estrogen and testosterone that promote bone growth and later on it will induce closure of these epiphysial plates so we know that bone is a dynamic living tissue and participates in what's known as bone remodeling 500 milligrams of calcium may enter leave the adult skeleton each day so guys make sure you are getting enough calcium either in your diet or through supplements bone matrix and osteocytes are continually removed and replaced cancellous bone of the skeleton is replaced every three to four years and compact bone is replaced every 10 years bone deposit and removal occurs at the periosteum and endosteal surfaces so the outer and inner surfaces of the bone bone remodeling is done through bone deposition which again is done by osteoblasts are accomplished by osteoblasts and then bone reabsorption breaking down a bone which is performed by the osteo class so within the spongy bone for example we can see remodeling occurring so we know that the trabeculae of the spongy bone is covered with that inner membrane called the end ostium and if we kind of zoom in we can see resorption of the bone matrix by osteoclasts that are along that and ostium and then we have deposition of new bone by osteoblasts okay so we have osteoclasts and osteoblasts within the bone that either will reabsorb bone by breaking it down or the osteoblasts will deposit new bone all occurring along the end ostium so just talking about the different cells that participate in bone remodeling we have the osteoclasts which are our bone degrading cell it's a giant cell with many nuclei curls along bone surfaces will break down bone tissue through secretion of concentrated hydrochloric acid also there are lies of zonal enzymes that help break down bone that are released from the osteoclasts and we know that osteoclasts are derived from matter poetic stem cells and then finally these osteoclasts apparently take up collagen and dead osteocytes through phagocytosis so here we see an osteo class this is the ruffled border of the osteoclasts which will break down the bone and the bone matrix through release of hydrochloric acid as well as lysosomal enzymes so here is that osteoclast so how does bone repair itself we have different types of fractures that it can occur in bone we have simple and compound fractures now a simple fracture is a fracture in which the bone breaks cleanly but does not penetrate the skin whereas a compound fracture is when broken ends of the bone will protrude through the skin and we have other types of other common types of fractures that include comminuted fractures compression fractures spiral epiphysial depressed and greenstick fractures and you can see this in table 6.2 and we did which we treat bone fractures through reduction which is the realignment of the broken bone ends in close reduction the bone ends are kind of manipulated back into position by the physician physicians hands in open reduction the bone ends will be joined surgically with pins or wires so after the bone is immobilized I'm sorry after the broken bone is reduced it is immobilized by cast or attraction to help allow for the healing process to begin and healing takes usually about six to eight weeks for a simple fracture but it may be longer for large weight-bearing bones and for bones of older people so here we see the different stages in the healing of a bone fracture first we have hematoma formation so fracture is usually accompanied by hemorrhaging we have broken blood vessels that break in the periosteum and inside the bone that will release clots to form what's known as a hematoma and we can see the stages of inflammation in and around the clot so here is that hematoma that was formed then we have a fibrocartilaginous callus formation so within a few days new blood vessels will grow into the clots um the periosteum in the end ostium near the fracture sites show a proliferation of bone forming cells which will then invade the clot and fill it with a repair tissue called soft callus so then we have the soft callus being called the fibrocartilaginous callus then we'll have a bony callus that forms so within a week that you're back laid up new one bone will begin to form and the callus mostly through endochondral ossification the callus is now called a bony callous or hard callus and that trabeculae will grow thicker and stronger and become firm in about two months after the injury then we have finally bone remodeling that occurs so if over a period of many months the bony callus is remodeled excess bony material is removed from both the outer bone shaft and the interior of the medullary cavity compact bone is laid down to reconstruct the walls of the shaft the repair area will resemble the original unbroken bone region because it responds to the same set of mechanical stresses so these are the stages of healing of a bone fracture and again table 6.2 shows the common types of fractures which you guys should be aware of we have a comminuted fracture where grown fragments into three or more pieces and are common in the old elderly whose bones are more brittle we have compression fractures where the bone is crushed these are common in porous bones or osteoporotic bones that are subjected to extreme trauma as an AFOL so here we can see compression fractures occurring within the vertebrae we have spiral fractures where a ragged break occurs when excessive twisting forces are applied to a bone and these are common in sports fractures we have epiphysial fractures where the epiphysial epiphysis will separate from the diaphysis along the epiphysial plates occurs where cartilage cells are dying and the calcification of the matrix is occurring we have depressed fractures where the broken bone portion is pressed inward this is a typical type of skull fracture usually due to trauma green strip fractures this is when the brain bone breaks skin completely much like how a green twig will break only one side of the shaft will break and the other side bends these are usually common in children because their bones have more organic matrix and are more flexible than those of adults so here we can see a break in one side of the bone but the other side has only bent as it's still relatively intact so then we have disorders of bones we have a disorder - many of you may know about called osteoporosis and osteoporosis is characterized by low bone mass what happens is bone reabsorption by the osteo class will occur more quickly than bone deposition by the osteoblasts and this often occurs in most women after menopause usually due to the decreased effects of estrogen after a certain age in women so here we can see the trabeculae abnormal bone strong trabeculae beams of spongy bone and then in osteoporotic bone so we can see these pores kind of infiltrating the trabeculae making the bones less firm and this is you due to a decrease in the amount of calcium as well as the effects a decrease effective estrogen on bone osteomalacia occurs in adults this is basically a vitamin D deficiency in adults bones are inadequately mineralized rickets is just the vitamin D deficiency in children so rickets occurs to children and is analogous to osteomalacia so basically it's just the vitamin D deficiency in children versus adults and here we can see the pathognomonic bowing of the legs of a child with rickets and this is again due to a vitamin D deficiency osteosarcoma this is a form of bone cancer osteosarcoma primarily affects young people between 10 and 25 years old usually originates in the long bone of the upper or lower limb with 50% of cases arising near the knee so basically the sarcoma is any cancer arising from a connective tissue cell or muscle cell and we know that osteo means bone so now we're going to talk about what occurs to the skeleton throughout life cartilage grows very quickly in youth the skeleton shows fewer chondrocytes in the elderly and basically we can use the bones as a time table we have me as a derm that gives rise to embryonic mesenchyme cells and the messing times will produce membranes and cartilage membranes and cartilage will ossify so here we see the primary ossification centers in the skeleton of a 12-year 12 week old fetus and we can see you know the different types of bones that will eventually become adult structures the cells skeleton grows until about 18 to 21 years old in children and adolescents bone formation will exceed the rate of bone reabsorption and young adults full information and bone reabsorption are in balance with one another and then in old age reabsorption will predominate and we know that as we get older bone mass declines that's why now you guys take care of your bones make sure you are getting enough calcium and vitamin D eating good healthy diets as well as getting enough exercise to build strong healthy bones okay and that is the chapter on bones