Connective Tissue Biomechanics Flashcards
1
Q
Connective Tissue Introduction
A
- 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
2
Q
Characteristics of Connective Tissue
A
- 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
3
Q
Functions of Connective Tissues
A
- 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)
4
Q
How Connective Tissue is Organized
A
- 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)
5
Q
Collagen
A
- most abundant CT
- greatest tensile strength (also withstands compression, torsion, etc)
- 20+ types
- type I and III most abundant
6
Q
Type I Collagen
A
- 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
7
Q
Elastin
A
- 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
8
Q
Reticular Fibers
A
- 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
9
Q
Ground Substance
A
- 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
10
Q
Classifying Connective Tissue
A
- 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
11
Q
Wolff’s Law
A
- 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)?
12
Q
Connective Tissue and the Musculoskeletal System
A
- 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
13
Q
Bones as Structures and Organs
A
- 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
14
Q
Biochemistry of Bone
A
- organic substances: 30%
- inorganic substance: 60%
- water: 10%
15
Q
Organic Substances of Bone
A
- 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
16
Q
Inorganic Substances in Bone
A
- calcium
- phosphorous
- magnesium
- sodium
- hydroxyl
- carbonate
- fluoride
17
Q
Enzymes
A
- 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)
18
Q
Anatomical Structure
A
- also called osseous tissue
- strong and resilient
- flexible collagen fibers
- hardened via calcium and salt deposits
19
Q
Regions of Skeletal System
A
- axial: cranium and vertebral column including hyoid, sternum, ribs, sacrum, and coccyx
- appendicular: UE and LE including scapula, clavicle, and illium
20
Q
Bony Structural Classification
A
- 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
21
Q
Types of Bone
A
- 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
22
Q
General Structure of Long Bones
A
- diaphysis
- metaphysis
- epiphysis
- epiphyseal plate
- periosteum
- medullary cavity
23
Q
Periosteum
A
- thin fibrous layer covering outer surface of diaphysis
- metaphysis, and epiphysis
- rich blood and nerve supply
- not present in areas covered by articular cartilage
24
Q
Medullary Cavity
A
- runs throughout diaphysis
- ends at epiphyseal plates
- lined with compact bone
- filled with bone marrow
25
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
26
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
27
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
28
Osteoblasts
- 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
29
Osteocytes
- 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
30
Osteoclasts
- large multinucleated
- capable of resorbing or removing bone
- remove organic matrix and calcium simultaneously
- responsible for deossification of bone
31
Blood Supply to Long Bones
- three distinct system exist
- afferent: nutrient and metaphyseal arteries supply inner 2/3 of cortex; periosteal arteries supply outer 1/3
- efferent vascular system: transports venous blood
- intermediate vascular system: capillary beds within cortex
32
Biomechanical Properties of Bones
- cortical bone stiffer than cancellous: 1.5-2% strain to failure for cortical and 50% for cancellous; cancellous has greater capacity for energy storage (elastic)
- tensile and compressive strength proportional to cross-sectional area
- stress fractures arise from secondary repeated minor trauma-related to tissue fatigue
33
Remodeling of Bone
- accomplished by simultaneous osteoblastic and osteoclastic activity
- must maintain bone balance: typically positive bone balance for children and often negative for elderly
- bone deposition in areas of stress and reabsorption from sites with little stress
- disuse results in bone loss known as osteopenia
- bone atrophy may occur with bed rest, prolonged inactivity, space travel, sedentary lifestyle
- genetically determined baseline mass for normal function: certain level of physical activity bone health
- decreased physical activity=bone loss
- weight bearing PA=bone growth
- too much intense PA problematic and optimal levels exist for each individual
34
Activity, Aging, and Bone Remodeling
- muscles help to dampen high tensile and compressive forces: eccentric mm action very important
- immobility leads to ~1% bone mass decrease per week
- for typical adult 35+ stress/strain tolerance, fracture toughness, and bending strength each decrease 2-3% every 10 years
35
Bone Remodeling and Exercise
- minimal essential strain: threshold stimulus for formation of new bone
- must be weight bearing to stimulate increases in bone density
- resistance exercise: variable results in studies when looking at bone mineral density; none focus on rate and magnitude of loading
- aerobic: high intensity repetitive activities like rowing, stair climbing, running have been moderately successful in demonstrating bone mineral density increases
36
Women and Bone Remodeling
- osteoporosis major societal health concern
- linked to menopause, age, and activity
- dietary habits as young adults play role
- female athletic triad: disordered eating, amenorrhea, and osteoporosis
- female athlete can have one, two, or all three parts of triad
37
Designing Interventions to Stimulate Bone Growth
- specificity of loading: perform exercise that stress part of skeleton where increases in bone density are desired; axial loading
- exercise selection: force vectors through spine and hip, multiple muscles, multi-joint, use greater absolute loads
- progressive overload: gradually increase training loads
- cross training: vary selection of exercises to vary distribution of forces
