l>BIOL 237 class Notes - skeleton System
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The SkeletalSystem
Bones space the organs of the skeleton system. Attributes of theskeletal mechanism are:support - it creates the body"s framework to assistance the muscles andorgans.protection - the skeletal systems protects by1) developing the bony cavities about organs, e.g. The thoracic cavity protects the love andlungs, thecranial cavity protects the brain.2) the red marrow in bones produces white blood cell which protect versus invadingmicroorganisms.movement - bones kind joints which carry out levers for activity such aswalking, lifting, etc.hematopoiesis (blood cell production) - the red marrow produces both redand white blood cells.mineral storage and also homeostasis - the skeleton forms a reservoir ofminerals, specifically calcium, formaintenance that homeostasis.
Cells discovered in bonetissue:osteoprogenitor cells - this are choose "stem cells" because that bone. They have thecapacity to divide andproliferate to form osteoblasts, bone forming cells which proactively producebone tissue. Lock comprisethe periosteal and endosteal cell (see below) which line the bone and its cavities. In mature bonewheregrowth and also remodeling is not arising these cells room quiescent, but they room thought come functioninmaintenance and nutritional support of the osteocytes in the basic matrix,with which lock connectby means of space junctions.Osteoprogenitor cell are acquired from mesenchymal cell (a fundamental embryologicalgerm tissue)and have actually the capacity to distinguish into adipose cells, chondroblasts, and also fibroblasts and also canmodifytheir morphologic (physical) and also physiologic characteristics in response to particular stimuli. osteoblasts - these room the "bone forming cells" i beg your pardon secrete the collagenand ground problem thatconstitutes invernessgangshow.netineralized bone (osteoid), and subsequently space responsible forcalcification the thematrix. These cells likewise communicate v one another and also with osteocytes by space junctions.Osteocytes are mature bone cells, differentiated from osteoblasts, whichare responsible because that maintainingthe bone matrix. They can synthesize and resorb (break down) the procession to maintainhomeostasis. Eachosteocyte occupies a space, the lacuna, i m sorry conforms to the shape of the cell surrounding bymatrixsecreted once the cell to be an osteoblast. Osteocytes prolong processes throughcanaliculi to connect toneighboring cell by means of void junctions.Osteoclasts are large multinucleated cell whose role is to resorbbone. Osteoclasts dissolve thematrix and osteoid with acids and hydrolytic enzymes. Osteoclasts room phagocytic and also are derivedfrommonocytes and not native the exact same line as the other bone cells.
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Tissues discovered inbones:osseous tissues - bone tissue properOsseous tissue has a matrix containing not natural salts and also organic fibers. Theinorganic matrix offers the rigidity and also hardness to bone and also is created of acombination the calcium and also phosphorus salts dubbed hydroxyapatite. Theorganiccollagen fibers provide a bone the tensile strength and resistance to stress.cortical (compact) bone - do of a thick regular plan of osteons(Haversian systems). Compact bone is uncovered in the diaphysis (shaft) of lengthy bonesand together the outer layer of every bones.cancellous (spongy) bone - consists of trabeculae (a network) that thin,connectingspicules which kind a meshwork in the inner of bones. Spaces between thetrabeculae save on computer marrow and also blood vessels.redmarrow - myeloid (blood producing) tissue discovered in the spaces in the spongybone, produces both red and also white blood cells. Red marrow go not boost inproportion to bone growth, and also in the adult much of the red marrow transforms 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 as in blood loss.periosteum - a fibrous spanning of bones which connects come tendons andligamentsand anchors blood vessels and also nerves. The inner class of the periosteum containsosteoprogenitor cells, derived from mesenchyme cells, this arethe cells whichdivide to become osteoblasts under appropriate stimuli. Really strongconnection is created with tendons and also ligaments since the collagen fibers fromthese structures, dubbed Sharpey"s fibers, prolong at an angle right into the bonewherethey are continuous with collagen yarn in the extracellular matrix.endosteum - fibrous tissue lining the medullary canal. Often only oncecells thickits cells are also osteoprogenitor cells.medullary canal - central canal the a long bone. It renders the bone lighterand inadults has yellow marrow.articular cartilage - hyaline cartilage i beg your pardon forms component of synovialjoints.
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Osteons, or Haversian systems, are theunits of framework in maturation bone. Lock aretightly i ordered it running normally parallel to the long axis of the bone. In ~ the centerof every is one Haversian canal i m sorry carries blood vessels and also nerves.Canaliculi(small canals) attach the Haversian canals v lacunae include theosteocytes.Osteocytes expand processes into the canaliculi and also receive nutrients and also O2 and also getrid the wastes and also CO2 by diffusion v the canaliculi. The lacunae andcanaliculi type lamellae or great of 2 types: concentric lamellaeform circularrings around 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): two varieties of bone breakthrough occur,differentiated by even if it is membrane or cartilage is the precursor because that the bone.Subsequent remodeling of both types renders similar tissues for all bones.Intramembraneous ossification wake up in the flat bones such as those in thecranium and also begins v a model of fibrous connective tissue. At around 8 weeksinto advancement the mesenchymal cells accumulation and differentiate to becomeosteoblasts and also begin the ossification process, first secreting the organiccomponents that bone (osteoid, made of collagen and also proteoglycans) as spikesradiating indigenous an ossification center. Later inorganic salts will be deposited on theosteoid to kind spicules that bone which kind trabeculae in the basic shape the thebone. Where the spikes meet irregular fibrous joints called sutures will be formed.Osteocytes extend their procedures through canaliculi while new osteoprogenitorcells maintain the number of osteoblasts for ongoing growth that the bone spicules.
See number 6.8
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Endochondral ossification is ideal exemplified in the longbones. (See figure 6.8):1) Mesenchymal cells aggregate and differentiate into chondroblasts whichproducea model of hyaline cartilage that precedes each bone. At around 8 mainly intodevelopment cells in the mid-region begin to identify into osteoblasts whichproduce a slim layer the bone around the cartilage model. In long bones a bone collardevelops around what will become the pillar (diaphysis). 2) Cartilage cells inthecenter hypertrophy and also cause calcification the the matrix, and also then dice as theybecome isolated from their nutrient source. With the death of the chondrocytes thematrix breaks down resulting in early on formation the the marrow cavity. 3) Bythethird month blood vessels referred to as the periosteal bud invade the developingcavitybringing in osteoprogenitor cells and also other cells and spongy bone and also marrowbegins to form. 4) At birth the lengthy bones covers a collar the cortical bonealongthe shaft and a emerging medullary canal. An additional ossification centers type inthe epiphyses which push outward and also to the center while osssification continuesalong the diaphysis toward the epiphyses. 5) Ossification that the epiphyses.Theproximal end begins near birth and also continues until 18 or 19 yrs. Of age. The distalend begins 1 come 1.5 years old and also continues till the at an early stage 20"s, although allsubstantial expansion has finished in the so late teens.The just remaining cartilage is in the epiphyseal plate and also the articular cartilage.Bone expansion stops as soon as the epiphyseal bowl hardens.
Bone Remodeling:Your bones space constantly remodeled throughout her life. This process helps to save themstrong and also tomaintain your integrity because that withstanding stresses, and maintaining homeostasis. The processinvolvesfirst osteoclastic resorption of one area of bone ,and then succeeding capillary penetration andosteoblastic activity to develop a brand-new osteon. In a healthy adult the price of resorption roughlyequals therate that bone deposition. In older civilization the rate of deposition frequently falls listed below that that resorptionandosteoporosis results. Bone remodeling is engendered by physical stress put on the bone byexercise,and will be tailored come provide particular adaptation to the stress. In that way a load lifter"s boneswillshow development patterns strange to the stresses placed on the bones.
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Hormones crucial to bone growth and homeostasis:growth hormone - native the anterior pituitary, this hormone is necessaryfor normalgrowth and breakthrough of the skeleton. A deficiency (hyposecretion) that GHduring childhood to produce a dwarf, an overabundance (hypersecretion) produce a giant.Hypersecretion in adulthood produces acromegaly, a disorder in which the form ofmany bones, specifically those in the challenge becomes exaggerated.thyroxine - this hormone, in reality its active product, regulates metabolismof mostcells including those in bone.testosterone - this and other androgens are necessary for expansion in massanddensity of bone. Testosterone is existing in both males and females in varyingamounts.estrogens - these hormones are necessary for expansion in size of bone andfor bonemaintenance. They as well are existing in varying quantities in both sexes.parathyroid hormone - this hormone exerts the primary manage in calciumhomeostasis. Calcium is vital in the blood for countless functions and when itslevel drops parathyroid hormone is secreted. This hormone provides several techniques toraise calcium levels in the blood: 1) raised Vitamin D production. VitaminD is ahormone who precursor is developed in the skin in an answer to sunlight and thenprocessed in the liver and also kidney to become active Vitamin D3. 2)Vitamin D3increases calcium absorb in the gut. Without this vitamin calcium is notabsorbed to any great degree. 3) increased reabsorption of calcium in thekidney.Much calcium is shed to the urine, so as soon as you need an ext in the blood this is animportant source. 4) resorption the bone. PTH boosts osteoclastic activity torelease calcium right into the blood.Calcitonin - Normally vital only in children, this hormone is secretedbyspecial cell in the thyroid. Its role is to stimulate the absorb of calcium intogrowing bone and also the deposition that bone matrix. It has actually been used in adults to help inthe absorb of calcium in osteoporosis patients.
Osteoporosis, a disorder involvingdemineralization that bone usually associated with larger individualscan be related to several factors:1) deficiency of dietary calcium2) diminished estrogen levels usual in post-menopausal women. This might be treated withHRT,hormone replacement therapy.3) reduced activity and exercise, including:4) diminished weight bearing stress and anxiety on the bones. This is crucial in stimulating bone growthandreplacement at any type of age.Osteoporosis treatment may incorporate calcium recipe with other minerals, hormonereplacementtherapy, calcitonin, and also an practice program.Other disorders:rickets - Vitamin D deficiency in children. Vitamin D is important forabsorption the calcium. The resultof rickets is not correct mineralization which results in stunted growth and weakened bones.osteomalacia - Vitamin D deficiency in adults. Reasons demineralization ofthe bones.

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Paget"s disease - a disorder the unknown reason which entails thedestruction of normal bone tissue andits replacement with tissue that irregular and unorganized structure. See Musculoskeletal Pathology Images
NOTE: these notes execute not encompass the bones and also contours girlfriend are required to recognize (See ShortList of Bones and Contours). Instructor will certainly go over plenty of of this in class, depending ontimeavailable.