l>BIOL 237 Class Notes - Skeletal System
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The SkeletalSystem
Bones are the organs of the skeletal system. Functions of theskeletal system are:support - it forms the body"s frame to assistance the muscles andorgans.protection - the skeletal devices protects by1) forming the bony cavities around organs, e.g. the thoracic cavity protects the heart andlungs, thecranial cavity protects the brain.2) the red marrow in bones produces white blood cells which protect against invadingmicroorganisms.movement - bones create joints which carry out levers for motion such aswalking, lifting, etc.hematopoiesis (blood cell production) - the red marrow produces both redand white blood cells.mineral storage and homeostasis - the skeleton forms a reservoir ofminerals, particularly calcium, formaintenance of homeostasis.
Cells uncovered in bonetissue:osteoprogenitor cells - these are prefer "stem cells" for bone. They have thecapacity to divide andproliferate to form osteoblasts, bone forming cells which actively producebone tissue. They comprisethe periosteal and endosteal cells (view below) which line the bone and also its cavities. In mature bonewheredevelopment and remodeling is not developing these cells are quiescent, however they are thshould functioninmaintenance and also nutritional support of the osteocytes in the underlying matrix,with which they connectby indicates of gap junctions.Osteoprogenitor cells are obtained from mesenchymal cells (a standard embryologicalgerm tissue)and have the capability to differentiate right into adipose cells, chondroblasts, and fibroblasts and canmodifytheir morphologic (physical) and physiologic features in response to particular stimuli. osteoblasts - these are the "bone forming cells" which secrete the collagenand also ground substance thatconstitutes princetoneclub.orgineralized bone (osteoid), and also consequently are responsible forcalcification of thematrix. These cells likewise communicate through one another and via osteocytes by gap junctions.Osteocytes are mature bone cells, distinguished from osteoblasts, whichare responsible for maintainingthe bone matrix. They can synthesize and also resorb (break down) the matrix to maintainhomeostasis. Eachosteocyte occupies a room, the lacuna, which condevelops to the shape of the cell surrounded bymatrixsecreted when the cell was an osteoblast. Osteocytes extend processes throughcanaliculi to attach toneighboring cells by indicates of gap junctions.Osteoclasts are big multinucleated cells whose feature is to resorbbone. Osteoclasts disdeal with thematrix and also osteoid through acids and also hydrolytic enzymes. Osteoclasts are phagocytic and are derivedfrommonocytes and also not from the exact same line as the various other bone cells.
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Tconcerns uncovered inbones:osseous tissues - bone tissue properOsseous tproblem has a matrix containing inorganic salts and also organic fibers. Thenot natural matrix provides the rigidity and also hardness to bone and is written of acombicountry of calcium and phosphorus salts dubbed hydroxyapatite. Theorganiccollagen fibers provide a bone its tensile toughness and resistance to stress and anxiety.cortical (compact) bone - made of a dense consistent plan of osteons(Haversian systems). Compact bone is found in the diaphysis (shaft) of long bonesand also as the external layer of all bones.cancellous (spongy) bone - Consists of trabeculae (a network) of thin,connectingspicules which create a meshjob-related in the interior of bones. Spaces between thetrabeculae contain marrowhead and blood vessels.redmarrow - myeloid (blood producing) tproblem uncovered in the spaces in the spongybone, produces both red and white blood cells. Red marrow does not rise inpropercentage to bone growth, and also in the adult much of the red marrowhead alters toyellow (fatty) marrowhead, specifically in the medullary canal.yellow marrowhead - Consists greatly of fat cells. It have the right to revert to red marrowunderexcessive hematopoietic anxiety, such as in blood loss.periosteum - a fibrous spanning of bones which connects to tendons andligamentsand also anchors blood vessels and nerves. The inner layer of the periosteum containsosteoprogenitor cells, acquired from mesenchyme cells, these arethe cells whichdivide to come to be osteoblasts under proper stimuli. An incredibly strongconnection is developed with tendons and ligaments bereason the collagen fibers fromthese frameworks, called Sharpey"s fibers, extfinish at an angle right into the bonewherethey are consistent via collagen fibers in its extracellular matrix.endosteum - fibrous tproblem lining the medullary canal. Often just oncecells thickits cells are additionally osteoprogenitor cells.medullary canal - central canal of a long bone. It provides the bone lighterand also inadults has yellow marrow.articular cartilage - hyaline cartilage which develops part of synovialjoints.
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Osteons, or Haversian systems, are theunits of structure in mature bone. They aretightly arranged running generally parallel to the lengthy axis of the bone. At the centerof each is an Haversian canal which carries blood vessels and also nerves.Canaliculi(little canals) attach the Haversian canals via lacunae containing theosteocytes.Osteocytes extend processes right into the canaliculi and receive nutrients and O2 and getrid of wastes and also CO2 by diffusion with the canaliculi. The lacunae andcanaliculi form lamellae or layers of 2 types: concentric lamellaeform circularrings approximately each Haversian canal, and interstitial lamellae, acquired frompreviousosteons, fill in the spaces in between existing osteons.
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See Figure 6.7
Bone formation(ossification): 2 kinds of bone development occur,differentiated by whether membrane or cartilage is the precursor for the bone.Subsequent remodeling of both forms provides identical tworries for all bones.Intramembraneous ossification occurs in the level bones such as those in thecranium and also starts through a version of fibrous connective tproblem. At around 8 weeksright into development the mesenchymal cells accumulation and also distinguish to becomeosteoblasts and also begin the ossification procedure, first secreting the organiccomponents of bone (osteoid, made of collagen and proteoglycans) as spikesradiating from an ossification facility. Later inorganic salts will be deposited on theosteoid to develop spicules of bone which create trabeculae in the general form of thebone. Wbelow the spikes accomplish ircontinual fibrous joints referred to as sutures will certainly be formed.Osteocytes extend their procedures via canaliculi while new osteoprogenitorcells keep the number of osteoblasts for continued development of the bone spicules.
See Figure 6.8
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Endochondral ossification is finest exemplified in the longbones. (See Figure 6.8):1) Mesenchymal cells accumulation and also identify right into chondroblasts whichproducea version of hyaline cartilage that comes before each bone. At about 8 weeks intobreakthrough cells in the mid-area start to distinguish into osteoblasts whichproduce a thin layer of bone about the cartilage model. In long bones a bone collarestablishes roughly what will end up being the shaft (diaphysis). 2) Cartilage cells inthecenter hypertrophy and also cause calcification of the matrix, and then die as theyend up being isolated from their nutrient resource. With the death of the chondrocytes thematrix breaks down resulting in beforehand development of the marrow cavity. 3) Bythethird month blood vessels called the periosteal bud invade the developingcavitybringing in osteoprogenitor cells and also various other cells and spongy bone and also marrowbegins to create. 4) At birth the lengthy bones consist of a collar of cortical bonealongthe shaft and also a emerging medullary canal. Secondary ossification centers form inthe epiphyses which press exterior and to the facility while osssification continuesalengthy the diaphysis towards the epiphyses. 5) Ossification of the epiphyses.Theproximal finish starts near birth and also proceeds until 18 or 19 yrs. of age. The distalfinish starts 1 to 1.5 years old and also proceeds until the early 20"s, although allextensive growth has finished in the late teenagers.The only continuing to be cartilage is in the epiphyseal plate and the articular cartilage.Bone growth stops as soon as the epiphyseal plate hardens.
Bone Remodeling:Your bones are constantly remodeled throughout your life. This process helps to store themsolid and also tomaintain their integrity for withstanding stresses, and keeping homeostasis. The processinvolvesinitially osteoclastic resorption of a space of bone ,and then succeeding capillary penetration andosteoblastic action to produce a brand-new osteon. In a healthy and balanced adult the price of resorption roughlyamounts to theprice of bone deplace. In older world the rate of deposition frequently falls listed below that of resorptionandosteoporosis results. Bone remodeling is engendered by physical tension put on the bone byexercise,and also will be tailored to administer particular adaptation to that stress and anxiety. In that method a weight lifter"s boneswillpresent development patterns peculiar to the stresses inserted on the bones.
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Hormones necessary to bone development and also homeostasis:expansion hormone - from the anterior pituitary, this hormone is necessaryfor normalgrowth and advance of the skeleton. A deficiency (hyposecretion) of GHin the time of childhood produces a dwarf, an excess (hypersecretion) produces a large.Hypersecretion in adulthood produces acromegaly, a disorder in which the form ofmany type of bones, particularly those in the face becomes exaggerated.thyroxine - this hormone, actually its active product, regulates metabolismof mostcells consisting of those in bone.testosterone - this and also other androgens are crucial for development in massanddensity of bone. Testosterone is present in both males and females in varyingamounts.estrogens - these hormones are necessary for expansion in size of bone andfor bonemaintenance. They also are current in varying amounts in both sexes.parathyroid hormone - this hormone exerts the major manage in calciumhomeostasis. Calcium is crucial in the blood for many type of attributes and as soon as itslevel drops parathyroid hormone is secreted. This hormone offers a number of methods toraise calcium levels in the blood: 1) increased Vitamin D manufacturing. VitaminD is ahormone whose precursor is developed in the skin in response to sunlight and also thenprocessed in the liver and also kidney to become energetic Vitamin D3. 2)Vitamin D3rises calcium absorption in the gut. Without this vitamin calcium is notsoaked up to any type of excellent level. 3) boosted reabsorption of calcium in thekidney.Much calcium is shed to the urine, so once you require even more in the blood this is anessential source. 4) resorption of bone. PTH rises osteoclastic task torelease calcium into the blood.Calcitonin - Generally necessary only in children, this hormone is secretedbyspecial cells in the thyroid. Its attribute is to stimulate the uptake of calcium intoprospering bone and the deplace of bone matrix. It has actually been provided in adults to assist inthe uptake of calcium in osteoporosis patients.
Osteoporosis, a disorder involvingdemineralization of bone generally connected with older individualscan be pertained to numerous factors:1) deficiency of dietary calcium2) reduced estrogen levels common in post-menopausal womales. This might be treated withHRT,hormone replacement treatment.3) diminished activity and exercise, including:4) decreased weight bearing stress on the bones. This is vital in stimulating bone growthandreplacement at any age.Osteoporosis treatment may incorporate calcium formulated via other minerals, hormonereplacementtreatment, calcitonin, and also an exercise routine.Other disorders:rickets - Vitamin D deficiency in children. Vitamin D is vital forabsorption of calcium. The resultof rickets is improper mineralization which outcomes in stunted development and weakened bones.osteomalacia - Vitamin D deficiency in adults. Caoffers demineralization ofthe bones.

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Paget"s disease - a disorder of unwell-known cause which involves thedamage of normal bone tissue andits replacement through tissue of irconstant and unarranged framework. See Musculoskeletal Pathology Images
NOTE: These notes perform not include the bones and contours you are compelled to recognize (See ShortList of Bones and Contours). Instructor will go over many type of of these in course, depending ontimeeasily accessible.