Connective Tissue Biomechanics Flashcards Preview

DPT 726: Orthopaedic Foundations > Connective Tissue Biomechanics > Flashcards

Flashcards in Connective Tissue Biomechanics Deck (37)
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Connective Tissue Introduction

-building block of bone, ligament, tendon, cartilage, joint capsules, IVD, nerves, etc
-tissues affected by: lifespan, injury, pathology, physical activity, hydration, sex
-understanding biologic and mechanical nature of these tissues provides insights necessary for prevention and management of injuries to these structures-better balance stress and recovery in these tissues


Characteristics of Connective Tissue

-framework upon which other tissues build functional units
-much different than epithelial tissues where cells are tightly adherent to one another
-has much different function than organs
-consist of dispersed cells that typically lack intercellular contact
-most are vascularized but less well than muscles or nerve tissues; cartilage is not vascularized
-EC spaces in CTs are more abundant and contain blood vessels
-CT represents 15-20% of total body weight and contains 20-25% of body's total water content


Functions of Connective Tissues

-connect epithelium to rest of body (basal lamina)
-connect and protect (tendon and ligament)
-provide structure and protect (bone)
-store energy (fat)
-transport materials (blood)
-repair following injury (scar tissue)


How Connective Tissue is Organized

-EC space is ECM: secondary accumulation of specialized cells
-these products include protein fibers and ground substances
-cellular: permanent components include fibroblasts, myofibroblasts, macrophages, mast cells, adipose cells; transient components include lymphocytes, plasma cells, basophils, neutrophils, eosinophils, and monocytes
-ECM: comprises functional characteristic of different fibers of connective tissue-fibers=collagen fibers, elastin fibers, reticular fibers; ground substances=mainly water, glycoaminoglycans (GAGs) and proteoglycans (PGs)



-most abundant CT
-greatest tensile strength (also withstands compression, torsion, etc)
-20+ types
-type I and III most abundant


Type I Collagen

-most common type
-accounts for ~90% of all collagen in body
-great tensile strength
-major type of collagen found in skin, tendon, bone, synovium and is also found in ligaments and muscle



-much greater elasticity than collagen
-allows tissues to stretch functionally: increases ability to withstand stress and undergo strain
-interwoven with collagen: prevents injury by increasing elasticity of tissues
-produced by fibroblasts and smooth muscle cells
-comprised of 2 parts: central elastin core and fibrillin microfibrils
-central elastin core: protein which forms fibrils which then intertwine to produce elastin fiber
-fibrillin microfibrils: surround central core, function to organize elastin fibrils into elastin fibers
-elastin fibers coil randomly in resting state, elongate in response to applied tensile force, recoil once load is released
-major CT in ligaments but found in many tissues throughout the body


Reticular Fibers

-found primarily in loose CT
-typically located at boundary of CT and epithelium
-also found surrounding muscles, blood vessels, and nerves
-similar to collagen fibers: contain collagen fibrils but made up primarily of type III collagen; contain more sugar groups
-have the least tensile strength of collagen and elastin
-produced by fibroblasts


Ground Substance

-occupies space between CT cells and fibers
-viscous, clear, gel-like substance
-GAG and PG are major components
-has high water content and little morphologic structure
-permits diffusion of oxygen, nutrients, cellular waste products; between the blood vessels and the cellular components of the CT
-gel-like consistency inhibits movement of large molecules and bacteria
-helps maintain interfiber distance within CT: critical for healthy CT
-hyaluronic acid is most abundant of the 7 GAGs found in our CTs
-GAGs have strong negative charge which attracts water --> bind to form gel-like consistency
-water is bound to GAG --> GAG bound to PG


Classifying Connective Tissue

-broadly classified into 3 groups: supportive connective tissue, connective tissue proper, and fluid connective tissue
-supportive: offers strength to structures; high levels in bone, cartilage, etc
-proper: serves to connect and protect and is divided into loose (much in muscle sheaths, epithelial tissue, fascia) and dense regular (tendons and ligaments) or dense irregular (joint capsules, periosteum, aponeuroses)
-fluid: transportation medium


Wolff's Law

-mechanical stress is the basis for bone architecture
-remodeling occurs in response to regular mechanical stress or lack thereof
-bone deposited in areas of high stress and resorbed in areas from sites of little stress
-considerable research over 100+ years supports this observation
-notion regarding mechanical stress applies also to other CT in MS system: tendon, ligament, cartilage
-health of all CT influenced by complex interaction of hormonal, metabolic, and biomechanical factors
-use it or lose it
-key to successful rehab is balancing positive mechanical stress to each patient's ability to recover metabolically
-forces PTs to continually eval and re-eval patients with the following questions
-are we prescribing adequate mechanical stress to maximize rebuilding/modeling of a damaged tissue?
-is the pt recovering from each dose of the mechanical stress?
-have we applied mechanical stress appropriate for the phase of tissue regeneration (acute, subacute/proliferation, chronic tissue regeneration/remodeling)?


Connective Tissue and the Musculoskeletal System

-bone is specialized connective tissue
-unique secondary to mineralization of ECM
-type I collagen is primary structural component of bone
-type V also very present
-I and V make up 90% of organic structure in bone matrix


Bones as Structures and Organs

-structures: provide rigid framework to withstand mechanical loads; serve as levers for locomotor function; protect internal organs
-organs: contain hematopoietic tissue; storage for Ca, P, Mg, Na; help maintain mineral homeostasis, help maintain blood
-both factors influenced by: age, site and shape of bone, dietary habits,presence of disease, sex


Biochemistry of Bone

-organic substances: 30%
-inorganic substance: 60%
-water: 10%


Organic Substances of Bone

-bone cells: osteoprogenitor, osteocytes, osteoblasts, osteoclasts; collagen fibers and non-collagenous proteins-95% of organic matrix
-matrix includes small quantities of reticular fibers and amorphous substances like hyaluronic acid and chondroitin sulfate


Inorganic Substances in Bone




-many enzyme systems in bone
-necessary for metabolism within bone
-i.e. bone alkaline phosphatase plays role in production of organic matrix before calcification (produced by osteoblasts)


Anatomical Structure

-also called osseous tissue
-strong and resilient
-flexible collagen fibers
-hardened via calcium and salt deposits


Regions of Skeletal System

-axial: cranium and vertebral column including hyoid, sternum, ribs, sacrum, and coccyx
-appendicular: UE and LE including scapula, clavicle, and illium


Bony Structural Classification

-long or tubular: humerus, femur
-short or cuboid: carpals, tarsals
-flat: cranium, scapula
-irregular: vertebrae, sphenoid, ethmoid
-each bone consists of cortical bone and porous cancellous or trabecular bone


Types of Bone

-compact: dense/cortical; forms outer shell of all bones
-cancellous: spongy/trabecular; surrounded by compact bone; found throughout inside of bone; composed of network of trabeculae; larger spaces in this network store primarily water, fat, and marrow


General Structure of Long Bones

-epiphyseal plate
-medullary cavity



-thin fibrous layer covering outer surface of diaphysis
-metaphysis, and epiphysis
-rich blood and nerve supply
-not present in areas covered by articular cartilage


Medullary Cavity

-runs throughout diaphysis
-ends at epiphyseal plates
-lined with compact bone
-filled with bone marrow



-red marrow consists of RBCs in various stages of development
-reticular cells and fibers also present, providing supporting network
-present in proximal and distal diaphysis of long bones as well as in marrow cavity
-amount of red marrow decreases as one matures


Micro Structure of Bone

-mature bone made up of haversian systems: aka osteons-number of circular districts run entire length of diaphysis in long bones parallel to bones long axis
-each haversian system has central hole surrounded by rings
-haversian canal is center of ring
-lamellae are the concentric rings
-lacunae are small cavities in gaps between each lamelle that house osteocytes
-canaliculi are additional canals through lamellae which cross lamellae at right angles and join lamellae within the same haversian system
-volkman's canals are large canals that pass through the bone aka perforating canals typically at 90% to haversian canals; pathway for blood and nerve supply which enters bone and can be differentiated from canaliculi as they pass through numerous haversian systems


Osteoprogenitor Cells

-located in deeper layer of periosteum
-also line cavities of endosteum, Volkman's canals, and haversian canals
-in immature bone divide and differentiate into osteoblasts
-in mature bone called resting cells; lay dormant until stimulated to differentiate into osteoblasts
-similar to stem cells



-bone forming cells essential for osteogenesis
-create and secrete matrix necessary for ossification which then lays foundation for calcification
-respond to mechanical stimulation-->bone growth and remodeling



-morphs from osteoblast after local formation of bone matrix, collagen, and ground substance
-a mature bone cell located in lacunae
-functions to maintain bone matrix



-large multinucleated
-capable of resorbing or removing bone
-remove organic matrix and calcium simultaneously
-responsible for deossification of bone