l>BIOL 237 course Notes - skeleton System
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The SkeletalSystem
Bones room the offal of the bones system. Attributes of theskeletal system are:support - it creates the body"s structure to support the muscles andorgans.protection - the skeletal equipment protects by1) developing the bony cavities around organs, e.g. The thoracic cavity protects the heart andlungs, thecranial cavity protects the brain.2) the red marrow in skeletal produces white blood cells which protect versus invadingmicroorganisms.movement - bones type joints which carry out levers for activity such aswalking, lifting, etc.hematopoiesis (blood cabinet production) - the red marrow to produce both redand white blood cells.mineral storage and homeostasis - the skeleton forms a reservoir ofminerals, specifically calcium, formaintenance of homeostasis.
Cells uncovered in bonetissue:osteoprogenitor cells - these are like "stem cells" for bone. They have thecapacity to division andproliferate to form osteoblasts, bone developing cells which proactively producebone tissue. They comprisethe periosteal and endosteal cell (see below) which heat the bone and also its cavities. In maturation bonewheregrowth and remodeling is not emerging these cells space quiescent, yet they space thought come functioninmaintenance and nutritional assistance of the osteocytes in the underlying matrix,with which castle connectby method of void junctions.Osteoprogenitor cells are acquired from mesenchymal cells (a an essential embryologicalgerm tissue)and have the capacity to identify into adipose cells, chondroblasts, and also fibroblasts and also canmodifytheir morphologic (physical) and physiologic features in an answer to specific stimuli. osteoblasts - these space the "bone developing cells" i beg your pardon secrete the collagenand ground substance thatconstitutes inter-base.netineralized bone (osteoid), and subsequently space responsible forcalcification the thematrix. These cells likewise communicate with one another and also with osteocytes by space junctions.Osteocytes room mature bone cells, distinguished from osteoblasts, whichare responsible because that maintainingthe bone matrix. They deserve to synthesize and resorb (break down) the matrix to maintainhomeostasis. Eachosteocyte occupies a space, the lacuna, which conforms come the form of the cell surrounded bymatrixsecreted when the cell was an osteoblast. Osteocytes expand processes throughcanaliculi to attach toneighboring cells by way of gap junctions.Osteoclasts are large multinucleated cells whose function is to resorbbone. Osteoclasts dissolve thematrix and osteoid v acids and also hydrolytic enzymes. Osteoclasts space phagocytic and are derivedfrommonocytes and also not native the very same line as the other bone cells.
Tissues uncovered inbones:osseous organization - bone tissue properOsseous tissue has actually a procession containing not natural salts and also organic fibers. Theinorganic matrix gives the rigidity and hardness come bone and also is created of acombination that calcium and phosphorus salts dubbed hydroxyapatite. Theorganiccollagen fibers offer a bone the tensile strength and resistance to stress.cortical (compact) bone - do of a thick regular setup of osteons(Haversian systems). Compact bone is uncovered in the diaphysis (shaft) of long bonesand as the external layer of every bones.cancellous (spongy) bone - consists of trabeculae (a network) the thin,connectingspicules which form a meshwork in the internal of bones. Spaces between thetrabeculae contain marrow and blood vessels.redmarrow - myeloid (blood producing) tissue discovered in the spaces in the spongybone, produce both red and also white blood cells. Red marrow does not increase inproportion come bone growth, and also in the adult much of the red marrow changes toyellow (fatty) marrow, specifically in the medullary canal.yellow marrow - Consists largely of fat cells. It can revert come red marrowunderextreme hematopoietic stress, such as in blood loss.periosteum - a fibrous spanning of bones i m sorry connects come tendons andligamentsand anchors blood vessels and nerves. The inner layer of the periosteum containsosteoprogenitor cells, obtained from mesenchyme cells, this arethe cells whichdivide to become osteoblasts under suitable stimuli. An extremely strongconnection is formed with tendons and also ligaments because the collagen fibers fromthese structures, called Sharpey"s fibers, prolong at an angle into the bonewherethey are consistent with collagen yarn in its extracellular matrix.endosteum - fibrous tissue lining the medullary canal. Frequently only oncecells thickits cells are likewise osteoprogenitor cells.medullary canal - central canal of a lengthy bone. It makes the bone lighterand inadults consists of yellow marrow.articular cartilage - hyaline cartilage which forms component of synovialjoints.
Osteons, or Haversian systems, are theunits of structure in tires bone. Lock aretightly arranged running generally parallel to the lengthy axis of the bone. In ~ the centerof each is an Haversian canal which carries blood vessels and also nerves.Canaliculi(small canals) connect the Haversian canals v lacunae include theosteocytes.Osteocytes extend processes right into the canaliculi and receive nutrients and O2 and getrid of wastes and also CO2 through diffusion with the canaliculi. The lacunae andcanaliculi kind lamellae or class of 2 types: concentric lamellaeform circularrings around each Haversian canal, and also interstitial lamellae, obtained frompreviousosteons, fill in the spaces in between existing osteons.
See number 6.7
Bone formation(ossification): two species of bone advance occur,differentiated by whether membrane or cartilage is the precursor for the bone.Subsequent remodeling that both types renders the same tissues for all bones.Intramembraneous ossification wake up in the level bones such as those in thecranium and also begins v a version of fibrous connective tissue. At about 8 weeksinto breakthrough the mesenchymal cells aggregate and identify to becomeosteoblasts and also begin the ossification process, an initial secreting the organiccomponents of bone (osteoid, make of collagen and also proteoglycans) together spikesradiating native an ossification center. Later inorganic salts will be deposit on theosteoid to form spicules that bone which type trabeculae in the general shape that thebone. Whereby the spikes fulfill irregular fibrous joints referred to as sutures will certainly be formed.Osteocytes extend their processes through canaliculi while brand-new osteoprogenitorcells preserve the variety of osteoblasts for ongoing growth the the bone spicules.
See number 6.8
Endochondral ossification is finest exemplified in the longbones. (See number 6.8):1) Mesenchymal cells aggregate and identify into chondroblasts whichproducea version of hyaline cartilage that comes before each bone. At around 8 weeks intodevelopment cell in the mid-region begin to identify into osteoblasts whichproduce a slim layer the bone roughly the cartilage model. In long bones a bone collardevelops approximately what will end up being the tower (diaphysis). 2) Cartilage cells inthecenter hypertrophy and cause calcification of the matrix, and then die as theybecome diverted from your nutrient source. Through the death of the chondrocytes thematrix breaks down resulting in early on formation of the marrow cavity. 3) Bythethird month blood vessels called 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 long bones consists a collar the cortical bonealongthe shaft and a developing medullary canal. An additional ossification centers type inthe epiphyses which push outward and also to the facility while osssification continuesalong the diaphysis towards the epiphyses. 5) Ossification of the epiphyses.Theproximal end begins near birth and continues until 18 or 19 yrs. Of age. The distalend begins 1 to 1.5 year old and continues until the early on 20"s, return allsubstantial development has ended in the late teens.The only remaining cartilage is in the epiphyseal plate and also the articular cartilage.Bone growth stops as soon as the epiphyseal bowl hardens.
Bone Remodeling:Your bones are constantly remodeled throughout your life. This process helps to store themstrong and also tomaintain their integrity because that withstanding stresses, and also maintaining homeostasis. The processinvolvesfirst osteoclastic resorption of one area of bone ,and then subsequent capillary penetration andosteoblastic action to produce a new osteon. In a healthy and balanced adult the rate of resorption roughlyequals therate of bone deposition. In older human being the rate of deposition regularly falls below that the resorptionandosteoporosis results. Bone remodeling is created by physics stress placed on the bone byexercise,and will be tailored to provide particular adaptation to that stress. In that means a weight lifter"s boneswillshow growth patterns strange to the stresses placed on the bones.
Hormones important to bone growth and homeostasis:growth hormone - from 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 to produce acromegaly, a disorder in i m sorry the form ofmany bones, particularly those in the challenge becomes exaggerated.thyroxine - this hormone, actually its energetic product, regulates metabolismof mostcells including those in bone.testosterone - this and also other androgens are vital for growth in massanddensity the bone. Testosterone is current in both males and females in varyingamounts.estrogens - these hormones are necessary for growth in length of bone andfor bonemaintenance. They also are present in varying amounts in both sexes.parathyroid hormone - this hormone exerts the primary manage in calciumhomeostasis. Calcium is essential in the blood for countless functions and also when itslevel falls parathyroid hormone is secreted. This hormone supplies several techniques toraise calcium levels in the blood: 1) enhanced Vitamin D production. VitaminD is ahormone whose precursor is developed in the skin in response 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 good degree. 3) enhanced reabsorption the calcium in thekidney.Much calcium is lost to the urine, so once you need an ext in the blood this is animportant source. 4) resorption of bone. PTH rises osteoclastic task torelease calcium into the blood.Calcitonin - Normally essential only in children, this hormone is secretedbyspecial cells in the thyroid. Its duty is to wake up the uptake of calcium intogrowing bone and also the deposition of bone matrix. It has been provided in adult to help inthe absorb of calcium in osteoporosis patients.
Osteoporosis, a disorder involvingdemineralization of bone usually associated with older individualscan be related to several factors:1) deficiency of diet calcium2) reduced estrogen levels typical in post-menopausal women. This might be treated withHRT,hormone replacement therapy.3) reduced activity and exercise, including:4) lessened weight bearing stress and anxiety on the bones. This is crucial in stimulating bone growthandreplacement at any kind of age.Osteoporosis treatment may incorporate calcium formulated with other minerals, hormonereplacementtherapy, calcitonin, and an practice program.Other disorders:rickets - Vitamin D deficiency in children. Vitamin D is necessary forabsorption the calcium. The resultof rickets is wrong mineralization which outcomes 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 of unknown cause which involves thedestruction of common bone organization andits replacement through tissue of irregular and unorganized structure. Check out Musculoskeletal Pathology Images
NOTE: this notes do not encompass the bones and also contours girlfriend are required to understand (See ShortList the Bones and also Contours). Instructor will go over many of these in class, escape ontimeavailable.