l>BIOL 237 class Notes - skeletal System
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The SkeletalSystem
Bones space the offal of the skeleton system. Features of theskeletal mechanism are:support - it creates the body"s frame to support the muscles andorgans.protection - the skeletal solution protects by1) developing the bony cavities about organs, e.g. The thoracic cavity protects the heart andlungs, thecranial cavity protects the brain.2) the red marrow in skeleton produces white blood cell which protect versus invadingmicroorganisms.movement - bones form joints which provide levers for activity such aswalking, lifting, etc.hematopoiesis (blood cabinet production) - the red marrow produce both redand white blood cells.mineral storage and homeostasis - the skeleton creates a reservoir ofminerals, specifically calcium, formaintenance that homeostasis.
Cells uncovered in bonetissue:osteoprogenitor cells - this are prefer "stem cells" for bone. They have thecapacity to divide andproliferate to type osteoblasts, bone developing cells which actively producebone tissue. They comprisethe periosteal and also endosteal cell (see below) which heat the bone and its cavities. In mature bonewheregrowth and also remodeling is not developing these cells space quiescent, however they room thought come functioninmaintenance and nutritional assistance of the osteocytes in the basic matrix,with which castle connectby way of gap junctions.Osteoprogenitor cells are obtained from mesenchymal cell (a fundamental embryologicalgerm tissue)and have actually the capacity to identify into adipose cells, chondroblasts, and fibroblasts and also canmodifytheir morphologic (physical) and physiologic characteristics in an answer to certain stimuli. osteoblasts - these room the "bone creating cells" which secrete the collagenand ground problem thatconstitutes moment-g.comineralized bone (osteoid), and also subsequently are responsible forcalcification of thematrix. These cells also communicate v one another and also with osteocytes by gap junctions.Osteocytes room mature bone cells, distinguished from osteoblasts, whichare responsible for maintainingthe bone matrix. They deserve to synthesize and resorb (break down) the matrix to maintainhomeostasis. Eachosteocyte rectal a space, the lacuna, which conforms to the form of the cell surrounded bymatrixsecreted as soon as the cell was an osteoblast. Osteocytes extend processes throughcanaliculi to connect toneighboring cell by way of gap junctions.Osteoclasts are huge multinucleated cell whose function is to resorbbone. Osteoclasts dissolve thematrix and also osteoid with acids and also hydrolytic enzymes. Osteoclasts space phagocytic and also are derivedfrommonocytes and also not native the very same line together the other bone cells.
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Tissues found inbones:osseous tissues - bone tissue properOsseous tissue has a procession containing not natural salts and organic fibers. Theinorganic matrix provides the rigidity and hardness come bone and also is composed of acombination of calcium and also phosphorus salts called hydroxyapatite. Theorganiccollagen fibers provide a bone its tensile strength and also resistance come stress.cortical (compact) bone - made of a thick regular plan of osteons(Haversian systems). Compact bone is discovered in the diaphysis (shaft) of long bonesand as the outer layer of every bones.cancellous (spongy) bone - is composed of trabeculae (a network) the thin,connectingspicules which type a meshwork in the interior of bones. Spaces between thetrabeculae contain marrow and blood vessels.redmarrow - myeloid (blood producing) tissue discovered in the spaces in the spongybone, to produce both red and white blood cells. Red marrow go not boost inproportion come bone growth, and also in the adult much of the red marrow changes toyellow (fatty) marrow, especially in the medullary canal.yellow marrow - Consists mostly of fat cells. It have the right to revert come red marrowunderextreme hematopoietic stress, such together in blood loss.periosteum - a fibrous covering of bones i beg your pardon connects to tendons andligamentsand anchors blood vessels and nerves. The inner layer of the periosteum containsosteoprogenitor cells, acquired from mesenchyme cells, this arethe cell whichdivide to become osteoblasts under proper stimuli. An extremely strongconnection is developed with tendons and ligaments since the collagen yarn fromthese structures, referred to as Sharpey"s fibers, expand at an angle into the bonewherethey are constant with collagen yarn in the extracellular matrix.endosteum - fibrous tissue lining the medullary canal. Regularly only oncecells thickits cells are also osteoprogenitor cells.medullary canal - main canal the a long bone. It provides the bone lighterand inadults contains yellow marrow.articular cartilage - hyaline cartilage i m sorry forms part of synovialjoints.
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Osteons, or Haversian systems, space theunits of structure in maturation bone. Castle aretightly i ordered it running normally parallel to the lengthy axis of the bone. At the centerof every is an Haversian canal which carries blood vessels and also nerves.Canaliculi(small canals) affix the Haversian canals through lacunae include theosteocytes.Osteocytes extend processes right into the canaliculi and receive nutrients and also O2 and also getrid that wastes and also CO2 by diffusion v the canaliculi. The lacunae andcanaliculi kind lamellae or class of 2 types: concentric lamellaeform circularrings roughly each Haversian canal, and interstitial lamellae, obtained frompreviousosteons, fill in the spaces in between existing osteons.
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See figure 6.7
Bone formation(ossification): two species of bone advance occur,differentiated by even if it is membrane or cartilage is the precursor for the bone.Subsequent remodeling of both types renders similar tissues for all bones.Intramembraneous ossification occurs in the level bones such as those in thecranium and begins with a design of fibrous connective tissue. At around 8 weeksinto breakthrough the mesenchymal cells aggregate and differentiate to becomeosteoblasts and also begin the ossification process, first secreting the organiccomponents the bone (osteoid, make of collagen and proteoglycans) as spikesradiating indigenous an ossification center. Later inorganic salts will be deposit on theosteoid to type spicules of bone which kind trabeculae in the basic shape of thebone. Wherein the spikes fulfill irregular fibrous joints referred to as sutures will be formed.Osteocytes extend their processes through canaliculi while brand-new osteoprogenitorcells keep the variety of osteoblasts for ongoing growth of the bone spicules.
See number 6.8
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Endochondral ossification is best exemplified in the longbones. (See figure 6.8):1) Mesenchymal cells aggregate and distinguish into chondroblasts whichproducea design of hyaline cartilage that comes before each bone. At around 8 weeks intodevelopment cells in the mid-region begin to differentiate into osteoblasts whichproduce a slim layer of bone approximately the cartilage model. In lengthy bones a bone collardevelops roughly what will come to be the obelisk (diaphysis). 2) Cartilage cell inthecenter hypertrophy and cause calcification the the matrix, and also then die as theybecome isolated from your nutrient source. With the death of the chondrocytes thematrix breaks under resulting in beforehand formation that the marrow cavity. 3) Bythethird month blood vessels called the periosteal bud invade the developingcavitybringing in osteoprogenitor cells and other cells and also spongy bone and also marrowbegins come form. 4) At birth the long bones consists a collar that cortical bonealongthe shaft and a occurring medullary canal. Second ossification centers type inthe epiphyses which press outward and to the facility while osssification continuesalong the diaphysis toward the epiphyses. 5) Ossification the the epiphyses.Theproximal end begins near birth and also continues until 18 or 19 yrs. That age. The distalend begins 1 come 1.5 years old and also continues till the early 20"s, although allsubstantial expansion has ended in the late teens.The just remaining cartilage is in the epiphyseal plate and also the articular cartilage.Bone development stops as soon as the epiphyseal key hardens.
Bone Remodeling:Your bones space constantly remodeled throughout her life. This process helps to save themstrong and tomaintain their integrity for withstanding stresses, and maintaining homeostasis. The processinvolvesfirst osteoclastic resorption of an area of bone ,and then subsequent capillary penetration andosteoblastic action to develop a new osteon. In a healthy and balanced adult the rate of resorption roughlyequals therate the bone deposition. In older people the rate of deposition regularly falls listed below that of resorptionandosteoporosis results. Bone remodeling is stimulated by physics stress placed on the bone byexercise,and will certainly be tailored to provide certain adaptation to the stress. In that method a load lifter"s boneswillshow development patterns peculiar to the stresses inserted on the bones.
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Hormones vital to bone growth and homeostasis:growth hormone - native the anterior pituitary, this hormone is necessaryfor normalgrowth and development of the skeleton. A deficiency (hyposecretion) the GHduring childhood to produce a dwarf, an excess (hypersecretion) produces a giant.Hypersecretion in adulthood produce acromegaly, a disorder in which the shape ofmany bones, especially those in the challenge becomes exaggerated.thyroxine - this hormone, actually its energetic product, regulates metabolismof mostcells consisting of those in bone.testosterone - this and also other androgens are vital for expansion in massanddensity that bone. Testosterone is existing in both males and also females in varyingamounts.estrogens - these hormones are essential for development in length of bone andfor bonemaintenance. They too are current in varying amounts in both sexes.parathyroid hormone - this hormone exerts the primary manage in calciumhomeostasis. Calcium is essential in the blood for numerous functions and when itslevel drops parathyroid hormone is secreted. This hormone provides several techniques toraise calcium levels in the blood: 1) enhanced Vitamin D production. VitaminD is ahormone whose precursor is created in the skin in an answer to sunlight and also thenprocessed in the liver and kidney to become active Vitamin D3. 2)Vitamin D3increases calcium absorb in the gut. There is no this vitamin calcium is notabsorbed come any great degree. 3) increased reabsorption that calcium in thekidney.Much calcium is shed to the urine, so once you need more in the blood this is animportant source. 4) resorption of bone. PTH increases osteoclastic activity torelease calcium into the blood.Calcitonin - Normally important only in children, this hormone is secretedbyspecial cell in the thyroid. Its function is to wake up the uptake of calcium intogrowing bone and also the deposition that bone matrix. It has been supplied in adults to assist inthe uptake of calcium in osteoporosis patients.
Osteoporosis, a disorder involvingdemineralization that bone usually linked with enlarge individualscan be pertained to several factors:1) deficiency of diet calcium2) lessened estrogen levels usual in post-menopausal women. This may be cure withHRT,hormone replacement therapy.3) reduced activity and exercise, including:4) decreased weight bearing tension on the bones. This is vital in stimulating bone growthandreplacement at any age.Osteoporosis therapy may encompass calcium recipe with other minerals, hormonereplacementtherapy, calcitonin, and also an exercise program.Other disorders:rickets - Vitamin D deficiency in children. Vitamin D is essential forabsorption the calcium. The resultof rickets is improper mineralization which results in stunted growth and weakened bones.osteomalacia - Vitamin D deficiency in adults. Causes demineralization ofthe bones.

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Paget"s disease - a disorder the unknown cause which requires thedestruction of normal bone organization andits replacement v tissue the irregular and unorganized structure. See Musculoskeletal Pathology Images
NOTE: these notes carry out not incorporate the bones and contours girlfriend are forced to understand (See ShortList that Bones and also Contours). Instructor will certainly go over plenty of of these in class, depending ontimeavailable.