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The Skeletal System: Skeletal Tissue

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The Skeletal System: Skeletal Tissue The Skeletal System: Skeletal Tissue Bone tissue forms most of the skeleton, the framework that supports and protects our organs and allows us to move. Remarkably strong but lightweight, bone is a dynamic, ever- changing tissue. Throughout life, it is constantly being broken down and reformed. Contents: -Cartilage -Bone -Ligaments Functions: 1. Internal Structural Support (framework of body) 2. Protection (ribcage, skull) 3. Permits Movement 4. MINERAL STORAGE (Ca, P, Na K) 5. Hemopocesis – formation of blood cells (red bone marrow) 6. Energy Storage (adipose tissue in yellow bone marrow) 1. Cartilage - a connective tissue -forms most of embryonic skeleton. Changes to bone prior to birth -some is found in adult skeleton ( end of ribs, ends of long bones) -AVASCULAR 1 a) histology of cartilage living cells called CHONDROCYTES (chondro = cartilage) -matrix is relatively rigid -contains both collagen and elastic fibers -within matrix are open spaces (lacuna), this is where the chondrocytes live -may or may not have protective outer sheath around tissue (perichondrium) b) hyaline cartilage the most common type of cartilage in body -frosty white in appearance -has perichondrium Located: ribcage, embryonic skeleton, ends of long bones also: trachea, larynx, nose and bronchi c) fibrocartilage a very stong and tough type of cartilage contains very densely packed collagen fibers can be compressed and recoil *lacks a perichondrium Located: between adjacent vertebra (disks) cushioning in joints (knee) 2 d) elastic cartilage a very flexible and elastic type of cartilage contains mostly elastic fibers has a perichondrium Locations: epiglottis, external ear 2. Bone - a connective tissue http://www.youtube.com/watch?v=RExT6pwZAWc Comprises about 20% total body weight 2nd strongest material in body (first is tooth enamel) OSTEOLOGY = the study of bone 3 a) histology of bone http://www.youtube.com/watch?v=c5zcGv8MvMc 1. Living Cells = OSTEOCYTES 2. live in open spaces in matrix called LACUNA 3. Bone matrix is totally rigid and 100% impermeable to diffusion 4. Composition: 1/3 collagen fibers and 2/3 calcium and phosphorus salt called HYDROXY APATITE 4 OSTEON: • Haversian Canal – long cylindrical tunnel in center of osteum. Contains blood vessels • Volkmann Canal - Side to side tunnels that link neighboring Haversian canals. Contain blood vessels • Lamella – circular plates of bone tissue that surround Haversian Canal • Canaliculi – tiny cracks in matrix that connect one Lacuna to another (like tentacles) FUNCTIONAL UNIT OF BONE TISSUE b) bone cells - osteoblast Function: synthesizes and secretes new bone matrix Location: areas of bone growth or repair - osteocyte Function: keeps bone tissue healthy and stable Location: lacuna Looks like an octopus “tentacles” are filopodia - osteoclast Function: breaks down old and worn out bone matrix (c for cuts) Location: areas of bone removal Very large multinucleate cell (fusion of many WBC’s) - osteoprogenitor cell Function: produces new osteoblasts * only bone cell capable of mitosis. 5 b) TWO DIFFERENT PHYSICAL ARRANGEMENTS OF BONE TISSUE compact bone *osteons are densely packed together, parallel to one another * no open spaces between adjacent osteons Location: external layers of all bones and central shaft of long bones Funciton: provides strength and rigidity to bones Physical protection of deeper marrow tissue Resists weight of body spongy bone (= cancellous bone) *osteons form a network of bars and struts (trabeculae) *osteons are stripped down to only a few lamellae around trabeculae and no canals *many open spaces filled with red bone marrow Location: inside end-caps of bones Inside many smaller bones (wrist, ankle) Function: provide space for hemopoiesis React to stresses placed on bones. 3. Ligaments strong bands of connective tissue that attaches bone to bone *dense regular connective tissue matrix is mostly bundles of densely packed collagen fibers ligaments appear dull white in color ----bone quiz #1 6 4. Typical long bone ( humerus, femur tibia) a) diaphysis a long hollow shaft of bone forms most all of the bones length made of a thick layer of compact bone midway, a small opening allows blood vessels to enter bone. b) epiphysis * a small endcap of bone at either end of diaphysis * for most long bones, they are: proximal epiphysis and distal epiphysis * made of compact bone as a thin outer shell and spongy bone as the filling inside * red bone marrow fills in spaces in spongy bone. c) articular cartilage * a thin layer of hyaline cartilage on surface of each epiphysis function: allows smooth, frictionless movement of bones and tendons in a joint * if it gets worn away becomes arthritis. d) epiphyseal plate • a thin pad of hyaline cartilage located in between the diaphysis and each epiphysis • one proximal one distal • Function: allows for bone elongation during growth years. In early 20’s, the cartilage turns into bone. • Bone elongation ends at this point • Renamed as epiphyseal line 7 e) medullary (marrow) cavity • hollow space inside of diaphysis • filled with yellow bone marrow • inactive red marrow infused with adipose tissue f) periosteum • an outer, tough protective membrane covering the surface of bone tissue • located everwhere except over articular cartilage • contains: nerves, blood vessels, osteoclasts, osteoblasts • Function: protection of bone tissue & solid attachment site for tendons & ligaments g) endosteum * an inner eark membrane lining inside a bone * lines inner wall of medullary cavity * contains: osteoclasts and osteoblasts HW: Skeletal 2 5. Bone growth bone growth involves mainly diaphysis because epiphysis is involved in joints (can’t change too much) a) growth in bone length a. chondroblasts add new cartilage at epiphyseal end b. osteoblasts turn “old” cartilage at diaphysis end into bone 8 b) growth in bone diameter a. periosteal osteoblasts deposit new bone matrix on outside b. endosteal osteoclasts destroy old bone matrix on inside. 6. Bone physiology * bone is a dynamic, living tissue * a) remodeling • a daily process in which bone tissue is added and removed in response to: o growth o repair o stresses placed on skeleton (24/7/365) *Osteoblasts and osteoclasts are active. c) fractures and bone repair Fracture: any significant break in a bone -bleeding occurs at site of fracture from torn blood vessels in periosteum inside osteons -a blood clot called a hemotoma forms at site of injury -fibroblasts and osteoblasts secrete new collagen fibers and new hydroxyapatite. Result: osteons are repaired stronger than before injury Video: broken bones 9 d) mineral storage - bone tissue is a major storage area for Ca andP in body - these minerals are added or taken away from bone as needed (diet and remodeling - about 99% Ca in body is stored in bones - remaining 10% is dissolved in blood or used in muscle cells for contraction. d) hormonal controls of mineral storage parathyroid hormone -secreted in response to low blood calcium Result: calcium released from boneà increases blood calcium calcitonin - secreted in response to high blood calcium - Result: excess calcium is added to boneà decrease in blood calcium human growth hormone - secreted during first 20 or so years of life - Result: stimulates osteoblasts to make new bone estrogen/testosterone (sex hormones) - secreted throughout most of life, especially during puberty - Result: stimulates osteoblasts to make new bone 10 7. Disorders of the skeletal system a) osteoporosis - condition in which osteoclast activity is greater than osteoblast activity - net loss of bone tissue leads to weakness and thinning of bones - increases the chance of bone fracture - common in middle-age or elderly women - onset of menopause (loss of estrogen) b) giantism and dwarfism -caused by an imbalance in human growth hormone ex: too much hormone à excessive bone growth à larger skeleton/tall stature ex: to little hormone à insufficient bone growth à smaller skeleton/short stature c) rickets a dietary disorder due to lack of vitamin D (remember – production begins in skin) *Vitamin D helps calcium and phosphorus absorption in digestive tract *if no vitamin Dàno Ca or P absorbed into body Secretion of parathyroid hormone causes Ca to be released from bones. Symptoms: weak, bendable bones, tooth loss. Common disorder in ancient sailors (poor diet) Treatment: fortify foods with Vitamin D. http://www.bbc.co.uk/news/uk-england-leicestershire-22531725 11 .
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