Chapter 6 Bones and Skeletal Tissues Flashcards
Skeletal Tissue in early development
- Skeletal initially made up of cartilage and fibrous membranes
- Bone replaces cartilage and in adult cartilage found where flexibility needed
Basic structure of Skeletal Cartilage
large portion is water no blood vessels or nerves surrounded by perichondrium appositional growth interstitial growth hyaline cartilage – most abundant skeletal cartilage o elastic cartilage o fibrocartilage
Perichondrium
Dense irregular connective tissue
- Contains blood vessels that supply nutrients to cartilage via diffusion.
Appositional growth
New matrix onto surface of existing cartilage from chondroblasts in the perichondrium
Interstitial growth
Chrondrocytes in existing lacunae divide and secrete more matrix
Hyaline cartilage types?
most abundant skeletal cartilage – forms:
Articular cartilage – covers ends of most moveable joints
Costal cartilage – connects ribs to sternum
Respiratory cartilage – forms framework of larynx and reinforce respiratory passages
Nasal cartilage – supports external nose
Elastic cartilage
Similar but more flexible than hyaline cartilage
- Contains elastin fibers in extracellular matrix
- Found in pinna (external ear) and epiglottis (cover larynx when swallowing)
Fibrocartilage
Highly compressible and great tensile strength
- Parallel rows of chondrocytes and thick collagen bundles
- Cushion areas subject to pressure and stretch
- Menisci of knees, pubic symphysis, intervertebral discs
Bones functions?
Provide:
- Support – framework that supports body
- Protection – surrounds brain and spinal cord and protects vital organs of thorax
- Anchorage – skeletal muscles attach to it by tendons – bones act as levers to allow movement
- Mineral and growth factor reservoir – calcium and phosphate – can be stored and removed from bone
- Hematopoiesis = blood cell formation – occurs in red marrow of bones
- Triglyceride storage – fat (energy) storage in yellow marrow of bones
- Hormone production – osteocalcin – helps regulate insulin secretion
Axial skeleton
Forms long axis of body
Skull bones, vertebral column, rib cage
Appendicular skeleton
Bones of upper and lower limbs and girdles (pectoral and pelvic) that attach them to the axial skeleton
Compact bone
Dense outer layer of bone – looks smooth and solid
Spongy bone
Honeycomb look with bone arranged on trabeculae – flat beams
-Spaces between trabeculae filled with marrow
Long bones structure
Diaphysis Epiphyses Epiphyseal plate Epiphyseal line Periosteum Endosteum
Long-bone Diaphysis
- Shaft – composed of thick collar of compact bone that surrounds
- Medullary cavity – contains yellow marrow in adults
Long-bone Epiphyses
-Bony ends that are broader than diaphysis
• exterior = compact bone
• interior = spongy bone – contains red marrow
• articular cartilage – covers joint surface
-Cushions opposing bone ends during movement
Long-bone Epiphyseal plate
Epiphyseal plate (“growth plate”) = disc of hyaline cartilage between epiphyses and diaphysis where lengthening of bone and linear growth occurs during childhood
Long-bone Epiphyseal line
Forms when epiphyses and diaphysis fuse in adult and linear growth ceases
Long-bone Periosteum
- Double-layered membrane surrounding external surface of bone (except on articular surface) - dense irregular connective tissue and osteogenic cells
- Rich supply of blood vessel and nerves
- Nutrient foramen = holes that allow blood vessels and nerves to penetrate shaft and enter marrow cavity
Long-bone Endosteum
-Delicate connective tissue layer (reticular) covers internal bone and trabeculae
Short bones
- Roughly cube shape
- Carpal and tarsal bones of wrist and foot
- Sesamoid bones – form in a tendon and act to alter angle of pull – patella, base of the thumb and great toe
Flat bones
- Thin, flattened and usually slightly curved
- Sternum, scapulae, ribs and most skull bones
Irregular bones
-Complicated shapes – coxal (hip) bones and vertebrae
Short, Irregular and Flat bone
-External layer of compact bone and filled with spongy bone (and red marrow)
Bone markings
- Projections that bulge from outward from surface – usually stresses created by muscles pulling on bone, or where bones meet to form joints
• head, trocanter, spine, tuberosity, line, crest, facet, condyle
-Depression and openings – allow blood vessels and nerves to pass, muscles to sit
• groove, fissure, foramen, notch, fossa
Bone Cells
osteogenic cells
osteoblasts
osteocytes
osteoclasts
Osteogenic cells
-Mitotically active stem cells found in periosteum and edosteum
Osteoblasts
-Mitotically active bone “building” cells that secrete bony matrix – when they become completely surrounded by bony matrix become osteocytes
Osteocytes
- Mature cells that sit in lacunae – monitor and maintain matrix
- Respond to mechanical stimuli – bone loading, deformation, weightlessness
- Communicate with bone remodelling cells (osteoblasts and osteoclasts)
Osteoclasts
“bone-clearing” cells - giant multi-nucleated cells with ruffled border
-Located at site of bone resorption and enzymatically degrade bone
Microscopia:
Compact bone: Osteon
Structure unit of compact bone
Microscopia:
Compact bone: Haversian system
- Group name for osteons
- Longated cylinder oriented parallel to the long axis of bone
Microscopia:
Compact bone: Lamellae
-Layers of bony matrix
• Each layer – collagen fibers in extracellular matrix run in same direction
• Adjacent layers – collagen in different orientation from neighbour
• Resists twisting (torsion) forces
Microscopia:
Compact bone: (Haversian) canal
In center of each osteon and contains blood vessels and nerve fibers
Microscopia:
Compact bone: Volkmann’s (perforating) canals
-Lie at right angles to the long axis of the bone and connect the blood vessels and nerves of the medullary cavity to the central canals
Microscopia:
Compact bone: Osteocytes
-Osteocytes lie in lacunae at the junctions of lamellae and canaliculi (hair-like channels) connect lacunae to each other
Microscopia:
Compact bone: Circumferential lamellae
-Extend around the entire circumference of the diaphysis
• located just deep to the periosteum and just superficial to the endosteum
Spongy bone
-Not as highly organized
-Trabeculae align precisely along lines of stress
Contain irregularly arranged lamellae and osteocytes connected by canaliculi
Osteogenesis and Ossification
Formation of bone
• embryonic skeleton prior to week 8 gestation = entirely fibrous membranes and hyaline cartilage
• bone tissue begins to replace cartilage during fetal period (beginning 9th week gestation)
• endochondral ossification (Fig. 6.8)– bone develops by replacing hyaline cartilage
o except for clavicle – all bones below the skull form by endochondral ossification
o hyaline cartilage must be broken down as ossification proceeds
-Long bone – primary ossification center – in the center of the diaphysis
-At birth – most long bones have a bony diaphysis surrounding remnants of spongy bone, a widening medullary cavity and two cartilaginous epiphyses
-Shortly after birth – secondary ossification centers – start in one or both epiphyses
-When secondary ossification is complete – hyaline only remains:
-On the epiphyseal surface as articular cartilage
- And at the junction of the diaphysis and epiphysis = epiphyseal plates
• Intramembranous – ossification begins within fibrous connective tissue membranes formed by mesenchymal cells at about 8 weeks gestation
-Forms cranial bones of the skull (frontal, parietal, occipital, temporal) and clavicles (flat bones)
Osteogenesis and Ossification
- Endochondral ossification – bone develops by replacing hyaline cartilage
- At birth
- Shortly after birth-secondary ossification centres.
-Intramembranous – ossification begins within fibrous connective tissue membranes formed by mesenchymal cells at about 8 weeks gestation
Infancy and youth
- Infancy and youth – long bones lengthen entirely by interstitial growth of the epiphyseal plate cartilage and its replacement by bone
- Epiphyseal plate maintains a constant thickness because rate of cartilage growth on epiphysis-facing side is balanced by replacement with bony tissue on diaphysis-facing side
- Longitudinal growth accompanied by consistent remodelling of epiphyseal ends to maintain proportion between epiphyses and diaphysis
- Involves both new bone formation and bone resorption
All bones grow in?
-All bones grow in thickness by appositional growth
- Osteoblasts beneath the periosteum secrete bone matrix on the external bone surface
- Osteoclasts on the endosteal surface remove bone
- Normally slightly more building up than breaking down
- Produces thicker, stronger bone but prevents it from getting too heavy
End of adolescence characteristics?
- Chondroblasts divide less often
- Epiphyseal plates become thinner and thinner until entirely replaced by bone
- Epiphyseal plate closure = when longitudinal bone growth ends as bones of epiphyses and diaphysis fuse and only articular cartilage remains
- Females ~18 years of age, male ~21 years of age
Adult Bone remodelling
- Recycle 5-7% of bone mass weekly
- Bone remodelling – bone deposit and bone resorption occur at the surfaces of both the periosteum and endosteum
- Controlled by genetics
- Calcium homeostasis mechanisms
- Mechanical and gravitational forces acting on the skeleton
- Hormonal controls determine whether and when remodelling occurs in response to blood calcium levels
- Mechanical stress determines where remodelling occurs
Adult Bone remodelling: Calcium homeostasis mechanisms
-Maintains blood Ca++ within narrow range
•Ca++ required for numerous physiological functions
•99% of found in bony matrix
•Hypocalcemia (low blood Ca++) – can lead to hyper-excitability, muscle cramps and spasms
•Hypercalcemia (high blood Ca++) – can lead to weakened bones, non-responsiveness, kidney stones
Mechanical and gravitational forces acting on the skeleton
•Keeps bones strong where stressors are acting
•Bending compresses bone on one side and subjects it to tension on the other
•Compression and tension minimal toward center of bone
-Can hollow out for lightness and use spongy bone
•Vigorous exercise leads to large increases in bone strength
Adult Bone remodelling:
- Hormonal controls
- Mechanical stress
-Hormonal controls determine whether and when remodelling occurs in response to blood calcium levels
-Mechanical stress determines where remodelling occurs:
spongy bone is replaced every 3-4 years
compact bone is replaced every 10 yrs
Adult Bone remodelling:
Hormonal regulation
- Growth hormone = most important hormone stimulating epiphyseal plate activity during infancy and childhood
- Hyper-secretion can result in gigantism
* Thyroid hormone – modulates growth hormone activity ensuring proper proportion of skeleton- Deficiency in growth hormone or thyroid hormone can result in dwarfism
- Hyper-secretion can result in gigantism
- Testosterone in males and estrogens in females – increase in amounts during puberty stimulating growth spurt
* Induces epiphyseal closure
-Calcium homeostasis
*Parathyroid hormone (PTH) – produced by parathyroid glands
• released when blood calcium levels decline
• stimulates osteoclasts to resorb bone – releases Ca++ into blood
*Calcitonin – produced by C cells of thyroid gland • less of an impact than rise and fall of PTH • released when blood Ca++ levels rise • suppresses osteoclast activity and enhances osteoblast activity
Adult Bone remodelling:
Hormones Involved?
- Growth hormone
- Testosterone in males and estrogens in females
- Calcium homeostasis
* Parathyroid hormone (PTH)
* Calcitonin –
Fractures and Bone Repair: Fractures
Fractures = bone breaks
Youth –trauma that twists or smashes bone (sports injuries, automobile accidents, falls)
Elderly – as bones thin and weaken
Fractures and Bone Repair: non-displaced fractures
Bone ends retain their normal position
Fractures and Bone Repair: Displaced fractures
Bone ends are out of alignment
Fractures and Bone Repair: Complete fracture
Bone broken all the way through
Fractures and Bone Repair: Incomplete fracture
Bone not broken all the way through
Fractures and Bone Repair: Open (compound) fracture
Bone ends penetrate the skin
Fractures and Bone Repair: (simple) fracture
Bone ends do not penetrate skin
Fractures can be described?
Can be described in terms of location, external appearance, and/or nature of fracture
Fractures and Bone Repair:
Treatment
- Reduction – realignment of the broken bone ends
* closed (external) reduction = physician’s hands realign bones
* open (internal) reduction = bones secured together surgically with pins or wires
-Immobilization = cast or traction
Fractures and Bone Repair:
Repair
- Hematoma forms = mass of clotted blood at fracture site
* Damage and tissue death lead to swelling, inflammation, and pain - Fibrocartilaginous callus forms
* Granulation tissue (soft callus) – capillary growth into hematoma, phagocytic cells invade
* Fibroblasts, cartilage and osteogenic cells arrive forming bulging fibrocartilaginous callus - Bony callus forms – within one week
* conversion of fibrocartilaginous callus to bony (hard) callus of spongy bone
* endochondral ossification process continues for about 2 months until firm union forms
-Bone remodelling occurs – excess material on diaphysis exterior and within medullary cavity is removed
Bone Disorders:
Osteomalacia
-Number of disorders where bones are poorly mineralized
calcium salts are not adequately deposited so bones are weak and soft
main symptom = pain when weight is put on affected bones rickets = disease in children and more severe than adult osteomalacia due to rapid growth of bones *bowed legs, deformities of pelvis, skull and rib cage caused by insufficient calcium in diet or vitamin D deficiency
Bone Disorders:
Osteoporosis characteristics?
-Group of diseases in which bone resorption outpaces bone deposit
bones become so fragile – strong sneeze or stepping off curb can break bone composition of the matrix remains normal bone mass decreases – becoming porous and light spongy bone of spine most vulnerable and compression fractures of vertebrae are common neck of femur very susceptible to fracture
Bone Disorders:
Osteoporosis risk factors?
-Aged – especially postmenopausal women
• 30% of all Caucasian women (most susceptible group) will experience bone fracture due to osteoporosis
• androgens (male) and estrogens (female) – sex hormones help maintain health and normal density of bone – restrain osteoclasts and promote osteoblast activity
*Estrogen deficiency strongly implicated in osteoporosis in older women
- Petite body form
- Insufficient exercise
- Poor diet – especially in calcium and protein
- Abnormal vitamin D receptors
- Smoking (reduces estrogen levels)
- Hormone-related conditions: Hyperthyroidism, low thyroid stimulating hormone, diabetes mellitus
Bone Disorders:
Osteoporosis Treatment?
- Supplemental calcium and vitamin D
- Weight-bearing exercise
- Hormone replacement therapy (HRT) – slows bone loss but increased risk of heart attack, stroke and breast cancer
- Bisphosphonates – decrease osteoclast activity and number
- Selective estrogen receptor modulators (SERMS) – e.g. raloxifene – estrogen-like effect but reduced side effects
Bone Disorders:
Paget’s Disease
- Excessive and haphazard bone deposit and resorption
- Abnormally high ratio of spongy bone to compact bone and reduced mineralization
- Spotty weakening of bones
- Osteoclast activity decreases but osteoblast activity continues – irregular thickenings
- spine, pelvis, femur and skull most often involved
- become increasing deformed and painful
-Cause unknown – may be viral induced - occurrence low, over age of 40
