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Exam two Chapter 6 

Hyaline Cartilage o Micrographs shows where the perichondrium is that outer wrapping of connective tissue that has a variety of elements associated with it and where its in contact with cartilage proper itself and you find progenitor cells or in this case chondrogenic cells (cell that becomes a chondroblasts)

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Growth patterns in cartilage (cartilaginous growth) o Grows in two ways o 1. Interstitial growth  growth from within  within cartilage tissue proper, we see a chondrocyte become mitotically active and it’s going to divide and those cells are now chondroblasts and those are going to lay down matrix and they push each other apart and the matrix will mature and they then they will become two separate chondrocytes  chondrocytechondroblastschondrocyte  the cartilage continues to grow internally  (this is within cartilaginous structure itself) o 2. Appositional growth  growth along edge of cartilaginous structure  stem cells, chondrogenic cells, etc. become chondroblasts and divide and lay down matrix and form cartilage along the periphery  (so this is along the periphery)

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 o these growths occur simultaneously during embryonic development o interstitial growth declines rapidly as cartilage matures  there are times when we don’t want that matrix to expand!  Growth later on would be appositional o When you become an adult, we don’t have cartilaginous growth but it will only be resumed if there is damage or injury but even then, it’lll be limited because of nutrient availability. o Cartilages are not vascularized so they need to get their nutrients from diffusion Enough about cartilage…BONE! o Each bone is its own individual organ, it’s a complex, dynamic structure o We’re going to see its primarily composed of bone tissue: osseous tissue as well as other tissues o Unique about bone is its matrix that is sturdy and rigid because of the presence of mineral deposition within ECM o Functions of Bone

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Structural and supportive type of element  Frameworks body is built upon  Protective in that we have the thoracic cage which wraps around delicate tissues like your lung or heart and other various structures  Protection from them from trauma or any injury  Movement  Attachment sites for skeletal muscle (slaughter house)  The bones apart of it serve as a series of levers that allow skeletal muscle to pull on that skeleton or bones to help with movement because remember muscle can only contract so it can only pull in one direction so how do I extend and flex my forearm? Because I have two different sets. Skeletal muscle pulls on that skeleton. o We can alter direction and magnitude of forces generated by skeletal muscle  Movement can be gross or precise o Moving arms- gross, precise- twitling my fingers  Hemopoisis  Within the substance called red bone marrow we have the formation of your blood cells, the process called hemopoesis  Which varies with age  Storage reserve  Storing minerals and energy  Calcium and phosphate o Responsible for storage and release of calcium and phosphate  Store fat (adipose tissue)- yellow bone marrow o Spongy bones o Classification of bones  Classified according to shape or place of development  shape  Long boneo Femur, humorous, o Length is greater than width o Elongated shaft called diaphysis and two bumpy on end called epiphysis  Short o Width and length are similar o Sesamoid bone- is a short bone found in a tendon that influences direction of pull within tendon and it can alter directional movements  Flat bone o Skull, frontal bone

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o Scapula o Thin, and flattened, bit of a curve, bone sandwich (two plates of compact bone with spongy bone in between) o Functionally: provide extensive SA for muscle attachment but also if you look at the skull, they are come together and provide protection for brain. Irregular bone o Elaborate, complex shape o Vertebrae o Doesn’t fall in any of the other categories

o Bone marking  Distinctive surface features, characteristics of that particular bone  Fall into categories  Articulating surfaces  Depressions  Projections  Opening and spaces  Functionality: serve as an attachment site and an entry site for nerves and vessels  Bone is hard and vascularized and innervated:  just understand what is a bone marking o General structure and gross anatomy for a Long bone  Proximal and distal epiphysis (attach tendons or ligaments)  Diaphysis: long cylindrical tube made of bone and provide us with leverage  Metaphysis: between the diaphysis and epiphysis which has an epiphyseal line that is an area of growth  Articular cartilage – epiphyseal ends- where joints are found – HYALINE cartilage  Open area along diaphysis- medullary cavity- vasculature and innervation, where bone marrow is found, bone wrapped around periosteumwrapping around bone of CT  Endosteum- inner layer and incomplete layer  Perforating fibers- originate from periosteum and invade into that outer layer of compact bone that we see on the long bone o Periosteum and endosteum  Periosteum  Outside wrapping of bone  Made up of two layers: outer fibrous layer (made up of dense irregular CT) and innercellular layer (finding osteoblasts or progenerative bone cells)  Isolates and protects bone  Anchors vasculature (blood vessels and nerves) too

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Mechanism to organize vasculature and nerves House osteoprogenitor cells and osteoblasts for bone growth and repair  Injury- fracture and needed to repair  Perforating fibers come out of periosteum  Osteoblasts and cells help lay down the bone away form the circumferential lamellae  Continuous with articulating cartilage Endosteum  Incomplete layer  Internally  Not as structured as periosteum  Made up of layer of cells, osteoprogenerative cells, stem cells, osteoblasts in osteoclasts which are important for bone growth, repair, and remodeling  Spongy bone- layer of different cell types (incomplete) osteoprogenerative cells, the osteoblasts, and osteoclast o Osteoprogenerator cells- bone stem cells  Drive from mesenchyme  Cell that is destined to become a bone cell  Initiated and utilized throughout life  They become an osteoblast o Osteoblast  Lays down matrix  Blast- laying down something  Matrix is the osteoid  When it lays down matrix, and the osteoid calcifies, it becomes an osteocyte  Build!! o Osteocyte  Hang out in its little room called a lacuna  Part of mature bone structure  Has these cytoplasmic extensions that radiate out from it?  Maintains, looks at health of bone, and can direct it to remodel, repair,  Serves as stress center  Exercise – you build healthier bone o Osteoclast  Arise from bone marrow and migrate here to this location,  Thought to have been derived from monocytes  They are huge and multinucleate cells

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Tear down, secrete hydrochloric acid to bleach out calcium and other minerals in bone and have lysosomes to tear down  Osteolyces  Tear down!! o You want osteoblast and osteoclast to balance each other

 o Matrix  Organic (1/3 of total)  Cells o themselves (osteocytes, osteoblasts, osteoclast) and the osteoid that surrounds it  osteoid o ground substance and collagen fibers o made AND secreted by osteoblasts  inorganic components  hydroxyapatites- (why bones are hard) a mineral salt, Ca phosphate interacts with Ca hydroxide and form hydroxyapatite. Which are crystals and form around and gather other salts and ions and they form around collagen fibers which gives bone its hardness.  Calcification – minerals around collagen fibers to give bone its hardness o Spongy and Compact bone  Compact- lamellar, dense, cortical bone  Spongy- cancellous, trabecular bone  3D arrangements of the different types of bone what do you see?  See compact bone peripherally and spongy bone on the anterior. Why? (long bone)

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Head of femur, articulating with synovial joint (ball and socket) so compact bone is designed to be a shield and take impact in one to two directions.  Spongy bone designed to handle stress in multiple directions  If you had a femur and it was all compact bone, it would be so heavy, spongy bone lightens weight Anatomy of compact bone  Periosteum on outside (2 layers) and fibers that anchor them on bone  Circumferential lamellae  Osteons- made up on cylindrical things – lamella –concentric  Whole- central canal running parallel –  Etc Osteon  Made up of plates of bone  Hollow tubes of bone matrix  Straw of one size, small straw, smaller  That form concentric lamellae  Collagen fibers arranged running in same direction but alternate between lamellae. Function?  allowing us to have a mechanism for twisting forces  Mineralize around collagen fibers  **mineralize collagen fibrils are interconnected by little bridges (or a gluelike filaments) (or sacrificial bonds of collagen)  so, collagen fibers that have salts on the outside and the bridges or bonds help to stabilize them  but when there is stress applied to bone these bridges break and we just build them back (SACROFICIAL BONDS)  so, we can distribute stress since we snap the bridge filaments and that distributes stress and we will build back more  great way to handle hard tissue you can put force against Anatomy of spongy bone  appears disorganized, has all these trabeculae, align along stress lines that are placed across this bone  adventitious: helps with distribution of applied forces of multiple directions so we don’t cause any damage.  Trabeculae only few cells thick  No osteons, have irregular lamellae called parallel lamella  Function is to reduce weight, support and protect marrow, cross bracing type of element for the bone itself Ossification  Internal framework (skeleton) determine size and proportions  Your bony skeleton begins to develop at 8 weeks of development  Bone can grow in thickness throughout life

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ossification in adults is primarily used for remodeling and repairing of any damage  Terms:  Osteogenesis- actual physical process of making bone  Ossification- generalized term (osteogenesis is a part of ossification) ossification is the process of replacing tissue with bone. You use cartilage as a template and fetus will use a couple of different tissue templates  Calcification- deposition of calcium salts o Intramembranous ossification  bone is made in developing fetus with two processes  1. intramembranous ossification also called dermal ossification  why it’s called this is because bone is going to develop by using a fibrous CT or a mesenchymal CT  basically, what we’re going to do is start out with a fibrous membrane being the template and this is going to result in membrane bone (making bone in a membrane type structure) this type of ossification leads to flat bone so, were going to see an Ossification center arise (area where we find osteoblasts) so were going to see within this mesenchymal membrane (this fibrous CT membrane) areas that are going to thicken and when they thicken, the mesenchymal cells are going to become osteoblasts and the osteoblasts lay down osteoid around them and we will see osteoid will undergo calcification.  So here is our ossification center and whenever there is an ossification center we will start building bone. So, when that osteoid calcifies were going to see the osteoblast mature to osteoclast. But notice osteoblasts are around center of ossification or bone being formed and continue to do so.  Thicken area of fibrous membrane our multiple ossification center that are directed within a certain region. We see multiple ossification centers link up with each other to form woven bone. Woven bone is also called primary bone within membrane and it’s an immature type of bone and it’s not well organized. It is within a certain section but within that region it’s not organized. It’ll start to form along the edges we see mesenchymal cells condense and form periosteum. Now starting to organize it and now we have lamellar bone or secondary bone. So, we organized primary bone so we have an outer compact bone with spongy bone inside.  Arise from mesenchymal cells  Lamellar bone- mature bone where we have compact and spongy bone and prior to that we had woven bone  Forming flat bones! Which use Intramembranous ossification for their development

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Steps: 1. 1. ossification centers form within thickened regions of mesenchyme. 2. osteoid undergoes calcification. 3. woven bone and surrounding periosteum form. 4. lamellar bone (compact + spongy bone) replaces woven bone. Second process: endochondral ossification  Arises from a cartilage template  Long bone, short bone, and irregular bones  Start with hyaline cartilage template with perichondrium around it  Within shaft (diaphysis) the chondrocytes start and undergo hypertrophy (enlarging) and reabsorb matrix around them so then that matrix then calcifies. and what happens is those chondrocytes within lacunae are going to now not be able to get any nutrients since calcification is blocking any nutrient flow. so, we have calcified cartilaginous shaft that has a bunch of holes in it. So, what’s going to happen is vasculature is going to move in this

area (bring osteoblasts and form the periosteum) and start and lay down bone on outside of structure forming a bone collar.  All arose because we had cartilage that calcified, the chondrocytes are lost, vasculature comes in, and it brings osteoblasts that lay down bone, and have a change from perichondrium to periosteum  Next, within region were going to start and set up primary ossification centers in the shaft region because we have calcified cartilage laying bone down around it and take a periosteal bud and go into spaces and the bud is going to bring osteoblast and osteoclast and osteogenesis occur in bone shaft  Epiphyseal ends invaded by vasculature which refers to secondary ossification center in these epiphyseal ends  Primary in shaft, secondary in epiphyseal ends, and regions of cartilage between them that is going to permit us to have growth occur in both ends (directions)  Growth occurs from shaft to both proximal and distal epiphyseal ends and that cartilage becomes your epiphyseal growth plate  Making of a long bone- primary and secondary ossification sites  If you’re making a short bone you only have primary ossification site  If you’re making an irregular bone you have primary ossification sites in many different locations simultaneously. But if you look at irregular bone and flat bone are similar but their starting template is different… flat bone: intramembranous process within a fibrous CT membrane…irregular bone: endochondral ossification using a cartilage template  http://www.dbriers.com/tutorials/2012/12/how-to-memorizeendochondral-ossification-simplified/  Boys Can’t Pee During Erections o Bone Collar Formation o Cavitation o Periosteal Bud Invasion o Diaphysis Elongation o Epiphiseal Ossification o Growth of bone  Long bone can also growth in length-(interstitial growth) and in diameter or thickness – (appositional growth)  Variety of things to influence bone growth- genes, metabolic factors, hormones present, mechanical stress, local tissue interactions, healthy childhood? medications- impact bone growth o Interstitial growth  Happening in epiphyseal growth plates (EP) – remaining areas of hyaline cartilage- that is found between bony diaphysis and bony epiphyseal ends

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5 distinct regions that are continuous  zone 1: o made up of cartilage, job is to serve as securing element to the epiphysis, helps to keep growth plate attached to epiphyseal ends  zone 2: o represents area of proliferation, rapidly growing cells increasing in numbers and size (hypertrophy) arranging themselves in longitudinal columns and stack themselves up. o Proliferation and hypertrophy occur together o Stacking in column and push ephyseal ends away from diaphysis--- increasing in length  Zone 3: o Matrix begins to calcify o Narrow deposits of minerals i.e. within matrix of columns of cells and because we calcify it that means we can’t get nutrients into those cells and the chondrocytes die. So, we end up with calcified channels and were going use them as a template. So, most of these channels are called longitudinal channels. (because they are longitudinal in form) And they are invaded by capillaries and osteopgenitor cells and were going to lay bone down on that calcified matrix frame. o Taking area and making bone upon it and remodel it and make what we need to find there (type of bone) o Always see in epiphyseal growth region- newly formed bone chasing cartilage formation o Build bone and push hyaline cartilage further away. So, you put down cartilage matrix and go through whole ossification process ending up forming new bone right behind cartilaginous structure o Epiphyseal cartilage/plate  As long as epiphyseal cartilage can grow and enlarge, the bone can continue to growth in length  Osteoblast are what’s going to be present to lay down new bone  osteoblasts and epiphyseal cartilage (chondrocytes) grow at the same rate  puberty- combination of hormones impacting various processes and cause bone to grow dramatically and they specifically target osteoblast that then start to outpace those chondrocytes (the cartilage forming cells) eventually bone will overtake all of the cartilage and when it disappears,

the epiphyseal growth has to stop- close- fine lines where plates used to be and open spaces are gone. Attained height that genetics have dictated  bone formation is equal with cartilage but puberty bone is faster than cartilage final length for bone structure o appositional growth  increases structures width  occurs in periosteum and along medullary cavity  osteoblast in periosteum they’re going to lay down layers or lamellae of bone on surface of bone (which forms circumferential lamellae)  ex. infant looks proportional so elements going into epiphyseal growth plate and have to address areas like the diaphysis. So, as we build on the outside we reabsorb on the inside so we can keep or retain the proper proportions o bone remodeling  in the adult, your bone is not static, there will be changes, which is referred to as remodeling because your bone continues to renew and grow throughout life  the process of bone remodeling is a continuously deposition of new bone and removal or reabsorption of old bone stimulated by stress (exercise and gravity) and occurs at both periosteal and endosteal surfaces  so, what we have here is within the bone there is a group of osteoclasts that open up a channel that’s followed by a group of osteoblasts that lay done bone and form an osteon. When that osteon is formed then the osteoblasts disappear and were going to vascularize through central canal as well as innervate.  So, bone remodeling allows us to modify architecture of bone and allow us to maintain calcium and phosphate levels.  20% of adult skeleton replaced yearly  as you age you remodel less  compact bone replaced slower than spongy bone  bone formation is going to outpace bone absorption  right now, bone formation and reabsorption occur equally but as you get older you start to lose bone. o Response to mechanical stress  Important because it stimulates remodeling  You make healthier bone by stressing your bone  Process that serves needs of skeleton  Follows wolfs law  Bone grows or remodels in response to applied forces and stresses placed upon it  Stress in two different directions: tension (laterally) and composition (medially)  Bone is a mechanosensitive organ which alters structure to suit its mechanical environment

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Mechanical loading generates pressure gradient that drive interstitial fluid through lacunar-canalicular system that is sensed by the osteocytes  Bone anatomy reflects applied stressed placed upon it, the more stress the healthier it’s going to be  Whole process_- mechanotransduction- take these physical forces placed on bones and convert to biochemical signals i.e. mechanosensitive ...