Chapter 6 Bone Tissue PDF

Ch 6 – Bone Tissue I. Intro to the Skeletal System – an organ system with tissues that grow and change throughout life a. Bones b. Cartilages – precursor to bone c. Ligaments – dense regular CT d. Other supportive tissues II. Cartilage: semi-rigid connective tissue a. Weaker than bone, more flexible...

Ch 6 – Bone Tissue I. Intro to the Skeletal System – an organ system with tissues that grow and change throughout life a. Bones b. Cartilages – precursor to bone c. Ligaments – dense regular CT d. Other supportive tissues II. Cartilage: semi-rigid connective tissue a. Weaker than bone, more flexible/resilient b. Avascular – mature cartilage, must remove waste via diffusion, limited healing c. Cell i. Chondroblasts: produce chondrocytes (fxnl cells of cartilage ii. Chondrocytes: maintain cell, produce ECM, reside in lacuna 1. Lacunae – spaces that house chondrocytes III. Functions of Cartilage a. Support soft tissues i. Airways – hyaline cartilage ii. Auricle (ear)– elastic CT b. Articulations i. Joints – hyaline cartilage covers end bones c. Precursor model for bone growth i. Fetal development IV. Bones: living organs with all 4 tissue types a. Primarily CT b. Extracellular matrix is sturdy and rigid (the only organ with solid ECM) c. Strengthened by calcification – minerals deposited in the matrix, main source & storage of Ca2+ and phosphates (PO4-) V. Function of Bones a. Support – framework/scaffolding b. Protection – covers vital organs (flat bones), ribs, skull, vertebral column c. Assistance in mvmt - levers d. Mineral storage and release e. Blood cell production – hemopoiesis / hematopoiesis (all new RBC’s produced in red bone marrow) f. VI. Triglyceride storage – yellow marrow comprised of fat Classifying Bones a. Long bones: length > width b. Short bones: length = width (carpals & tarsals) c. Flat bones: thin surfaces - cranium, sternum d. Irregular bones: vertebral column, sacrum, innominate, facial e. Sesamoid bones: within tendon (floating), patella f. VII. Sutural bones: b/n sutures in cranial bones Long Bone Anatomy a. Diaphysis – long cylindrical shaft i. singular b. Epiphyses i. At ends - knobby ii. Strengthens joints iii. Attachment site for ligaments / tendons d. Metaphysis i. Between diaphysis and epiphyses ii. Contains epiphyseal plate, becomes line/scar when stops growing di. Articular cartilage i. Thin layer of hyaline covering epiphysis ii. Reduces friction dii. Periosteum i. CT: dense irregular ii. Covers external surfaces of bones, except where there is articular cartilage 1. Does not cover joint surfaces iii. Anchor for VAN’s diii. Medullary cavity i. In diaphysis ii. Usually contains yellow marrow div. Endosteum i. Covers most medullary cavity ii. Single layer of cells (bone building osteoblasts) iii. Under torsional force as cells lay down new bone VIII. Bone Surface Markings (osseus landmarks) a. Depressions( fossa, groove) and openings (foramen, meatus, canal) i. Form joints or allow passage of VANs b. Processes, projections of outward growth i. Serve as attachment sites for tendons & ligaments c. See table 6.1 for specific terms IX. Histology of Bone Tissue a. Bone Matrix i. 40% organic components 1. Cells 2. Collagen fibers (mostly) Like rebar – gives flexibility yet resists bending 3. Ground substance ii. 60% inorganic components 1. Calcium phosphate [Ca3(PO4)2] Hydroxyapatite – provides rigidity 2. Calcium hydroxide [Ca2(OH)2] b. Bone Cells i. Osteoprogenitors: develops into mature bone cells, found in periosteum/endosteum, mitotic cells produced ii. Osteoblasts: form bone matrix, builders iii. Osteocytes: reside in lacunae, mature bone cells, - Communicates with each other via canaliculi iv. Osteoclasts: bone crushers & carvers, large multinucleated cells (~30) resorb bone matrix X. Resorb Ca2+ into the bloodstream Comparing Bone Tissues a. Compact bone (cortical or dense bone tissue) i. Dense & solid to the unaided eye, but is porous looking under the microscope ii. External surface: flat bones have 2 layers with spongy bone in between (clavicle) b. Spongy bone (trabecular or cancellous bone tissue) i. Trabeculae – open latticework of narrow plates ii. Internal surface iii. Abundant in epiphysis (forces coming in all directions) iv. 2 unique char: light & supports/protects red bone marrow (hip bones, ribs, sternum, vertebrae, prox humerus/ femur) XI. Compact Bone Organization a. The basic sx & fxl unit of mature compact bone is the osteon i. Cylindrical ii. Parallel to the shaft XII. Osteon Components a. 3 Types of Canals i. Central (AKA osteonic or haversian): in center of osteon ii. Perforating (AKA Volkman or interosteonic): perpendicular to central canal - Contains VAN’s iii. Canaliculi: b/n lacunae, allows metabolic interaction b/n osteocytes b. Lamellae (sheets of compact bone) i. Concentric – around central canal, concentric plates of bone forming osteon ii. Circumferential – around perimeter of bone along endosteum & periosteum iii. Interstitial – left overs / plates of bone forming the osteon and old replaced osteons XIII. Blood and Nerve Supply a. Arteries (aa) & Veins (v.v.) i. Periosteal: enter periosteum in diaphysis through interosteonic (perpendicular) canals ii. Nutrient: enters dominant away from growth end of bone (go to the elbow, flee the knee) iii. Metaphyseal: b/n diaphysis & epiphyseal plate iv. Epiphyseal: in epiphysis, supplies red bone marrow b. Nerves i. Accompany blood vessels ii. Periosteum – rich in nerve supply XIV. Ossification: the formation and development of bone a. A.K.A. Osteogenesis b. Begins 6th - 8th week of embryonic development and continues into adulthood i. 3 initial germ layers 1. Endoderm – epithelial tissues 2. Mesoderm – skeletal, cardiac, smooth ms; bone, blood, dermis, kidneys, ureters, adrenal cortex, dura mater 3. Ectoderm – epidermis, nervous tissue, melanocytes, skeletal & CT of head c. 2 general patterns i. Intramembranous ossification 1. Develops from mesenchyme 2. Produces flat bones of the skull, some facial bones, the mandible, and central portions of clavicle 3. 4 stages of Intramembranous ossification a. Development of ossification center (mesenchymal cells cluster > osteoprogenitor > osteoblast) b. Calcification – secretion of ECM stops > osteocytes formed > Ca2+ deposited into ECM c. Formation of trabeculae – form around blood vessels (CT surrounding this, becomes red bone marrow) d. Development of periosteum – from surrounding mesenchyme, surface layers develop compact bone ii. Endochondral ossification 1. Begins with a hyaline cartilage model 2. Produces the majority of bones in the body 3. 6 stages of endochondral ossification (Hyaline cartilage model) a. Development of cartilage model – chondroblasts secrete ECM (hyaline cartilage), perichondrium develops in diaphysis b. Growth of cartilage model – cell division of chondrocytes i. > interstitial growth (from within, ↑ length) ii. > appositional growth (from perichondrium, ↑ width). As chondrocytes hypertrophy they get further from blood supply and start to die due to calcification of ECM. c. Development of primary ossification center – 6-8th wk, diaphysis calcifies first (periosteum) - Proceeds inward from external surface, nutrient artery penetrates perichondrium at mid diaphysis, stimulates osteoprogenitor cells to form osteoblasts - Periosteal capillaries > 1o ossification center: osteoblasts form spongy bone d. Development of medullary cavity – osteoclasts break down trabeculae, most diaphysis replaced by compact bone e. Development of secondary ossification centers (epiphyses) – epiphyseal plate in childhood consists of cartilage from epiphyseal arteries (about time of birth), no medullary cavity, bone growth outward f. Formation of articular cartilage & epiphyseal plate (both hyaline cartilage). Epiphyseal plate only remains hyaline cartilage through interstitial growth. XV. Bone Growth During Infancy, Childhood & Adolescence a. Growth in Length i. Interstitial growth of cartilage on epiphyseal side of plate + replacement of cartilage by bone on diaphyseal side (grows into diaphysis) ii. Epiphyseal plate 1. Layer of hyaline cartilage on metaphysis 2. 4 zones a. Zone of resting cartilage: closest to epiphysis, small chondrocytes b. Zone of proliferating cartilage: large chondrocytes, ↑↑ mitosis, “stack of coins” c. Zone of hypertrophic cartilage: growth in size, no more mitosis d. Zone of calcified cartilage: deposited minerals (Ca2+), kill chondrocytes (apoptosis) b. Growth in Thickness i. Appositional growth = growth in width, occurs throughout lifespan 1. Periosteal cells differentiate into osteoblasts > secrete collagen fibers & organic molecules (ECM) >endosteum 2. Forms tunnel around blood vessels – former periosteum becomes endosteum surrounding blood vessels 3. Osteoblasts continue secreting ECM > concentric lamellae (from osteoblasts in endosteum) 4. Osteon forms with continued layers 5. Osteoclast destroy bone tissue in medullary cavity, increasing inner diameter as outer widens XVI. Remodeling of Bone: replacement of old bone tissue with new bone tissue a. Resorption: removal of Ca2+ (minerals) & collagen fibers by osteoclasts b. Bone deposition addition of Ca2+ (minerals) & collagen fibers by osteoblasts c. 5-10% of bone mass replaced yearly: compact 4%, spongy 20%, distal femur q 4mos, never shaft d. Benefits: new bone is stronger, bone can change shape depending on stress load e. Orthodontics – ↑ stress by braces > remodeling f. Osteoporosis – middle aged/elderly, females > males, ↓hormone production, ↓ activity i. Treatment: 1. antiresorptive drugs – bisphosphonates, selective estrogen receptor modulators, estrogen & hormone replacement therapy 2. bone building drugs (Forteo – PTH synthetic) g. Fractures XVII. Factors Affecting Bone Growth/Remodeling (Table 6.3) a. Exercise: bone responds to mechanical stress (s kms & grav /WB) b. Diet & Lifestyle c. Hormones i. Growth Hormone: stimulates epiphyseal plate & osteoblast (dwarfism & giantism) ii. Thyroid Hormone: ↑’s osteoblastic activity iii. Calcitonin (also from thyroid): (↓ osteoclastic activity) iv. Parathyroid Hormone: (↑ osteoclast activity) v. Sex Hormone: estrogens (female), testosterone (male) > ↑ osteoblast (growth spurt), slows in adulthood vi. Cortisol: releases Ca2+ into bloodstream, naturally released in times of stress 1. Glucocorticoids (prednisone) d. Vitamins i. Vit A: ↑ osteoblasts ii. Vit C: ↑ collagen (get scurvy if you don’t have enough!) iii. Vit D (hormone): promotes Ca2+ and phosphorus absorption in intestine (low levels/ ↓ sun exposure leads to Rickets > bone softening) iv. Vit K & B12: synthesis of bone proteins (deficiency > decreased bone density) XVIII. Fractures = any break in the bone a. Common Types i. Open (compound) ii. Comminuted – splintered / crushed iii. Greenstick – partial, bone is bent, one side fx’d, other not, found more in children iv. Impacted – one end of fx driven into the other v. Pott – distal fibula w/ injury to distal tibial articulation vi. Colles – distal radius displaced posteriorly b. 3 Steps to Repair Bone Fx i. Reactive Phase – fx hematoma 6-8 hrs post injury, nearby cells die, phagocytes and osteocytes clean up remains ii. Restorative Phase – formation of fibrocartilaginous (3 wks) and bony (3-4 mos) callus 1. Bony callus: osteoprogenitor cells become osteoblasts > produce spongy trabeculae joining fibrocartilage > spongy bone iii. Bone remodeling Phase – dead portions absorbed by osteoclasts, compact bone replaces spongy bone in periphery XIX. Aging a. Birth > adolescents: osteoblasts outpace osteoclasts b. Young adults: bone deposition = bone resorption c. Middle age: bone resorption > bone deposition (sex steroids diminish > menopause) d. Old age: bone resorption >> bone deposition, women’s bones most affected, as they start with less mass e. Two principles effects of aging i. Demineralization: > loss of bone mass (Ca 2+, begins at age 30 women - 8%/10yr; men start at 60yr, 3%/10yr) ii. Brittleness: ↓ rate of protein synthesis (collagen fibers), influenced by ↓Growth Hormone