2. Skeletal System. Aged Osteoporosis (post menopausal fractures - decreased bone density/ length) Loading Effects. Wednesday, 17 June 2015

Transcription

1 BIOL1900 Page 1 2. Skeletal System Wednesday, 17 June :32 am Bones Very Strong Not inert i.e. grow/ decrease in size Compression strength ~170MPa (Steel ~300Mpa, aluminium ~80MPa) Lower tensile strength ~ Mpa Very low shear stress strength ~50Mpa Bone Stress Fractures (Overuse) Cumulative micro damage Excessive training/ inadequate recovery ('fatigue' fractures) Prevention role for HMS professionals Stress Fractures across the lifespan Children Greenstick fractures - young, 'softer' bone which bends and partially breaks Bones become harder 'calcified' and more brittle with age Young children 61% mineral content Middle aged adults 66% mineral content Adolescents Dissociation between timing of peak linear growth and peak bone mineral acquisition - clinical significance during this short lag time is a temporary period of relative skeletal weakness Adolescent fracture incidence is at a peak during this period Aged Osteoporosis (post menopausal fractures - decreased bone density/ length) Loading Effects

2 BIOL1900 Page 2 Bone is metabolically active - responds to mechanical stimuli by initiating or inhibiting bone remodelling Animal and human studies - key features for osteogenic stimuli include load that is dynamic, have high magnitude, high frequency and unusually distributed Loading Effects Studies on Growing Animals Response of growing bone in young animals to moderate and intense physical activity thoroughly reviewed Animal studies are incontrovertible in showing that growing bone has a greater capacity to add new bone than the bone of adults Maturity and Sex Dependant Loading Responses Prepubertal skeleton seems to have capacity to respond to loading by adding more bone in periosteal (between skin and bone) surface Prepubertal boys show endosteal apposition in response to mechanical load whereas such as response seems less likely in girls

3 BIOL1900 Page 3 Bones - Segmental Growth In terms of total leg length: More growth occurs in the femur than in the tibia (55% vs 45%) Also 2/3 more growth occurs at the knee end of the long bones than at the hip and ankle ends (67% vs 33%) Bones - Maturational Differences Femoral Angle of Inclination ~ degrees in young ~120 degrees in young Coxa valga often combined with genu varum (bow-leg) Coxa vara often combined with genu valgum (knock-knee) Kids have different skeleton when born and have walking problems etc. Human Skeleton Adult skeleton 206 bones ~270+ at birth Hands and feet: ~half of the bones in skeleton Femure: longest, heaviest, strongest bone. Length ~25% of an individuals height, reasonable estimate of height of incomplete skeleton Appendicular Skeleton 126 bones Involved in movement through levers Axial Skelton 80 bones Involved in support and protection

4 BIOL1900 Page 6 3. Muscular System Thursday, 12 March :02 am Understanding Muscle Function Biceps Curl Agonist - Brachioradialis, biceps brachii and anterior deltoid Synergist - Coracobrachialis Stabilizers - rotator cuff Antagonist - Triceps Muscle Size and Loading Some people born with genetic predisposition to have stronger, larger faster muscles This muscle growth is regulated by myostatin Muscle size and strength is also affected by hormones e.g. peptide hormones (growth hormones, insulin) Environmental factors such as nutrition also have significant impact. If muscles are unloaded (e.g. space) it will have a negative affect on muscle and bone. Malnourishment also restricts growth Physical Inactivity When muscles are immobilized/ unweighted (e.g. limb casting, bed-ridden, micro-gravity) there is a significant response from the muscles Decrease in muscle CSA (30% atrophy in 11 days) and a decrease in length Following major surgery (e.g. total knee arthroplasty) most significant clinical barrier is persistent muscle atrophy and weakness Quadriceps as much as 40% weaker 2 months post surgery compared to healthy individuals Physical Activity Muscle hypertrophy is not stimulated by long distance low intensity exercise Marathon running, endurance cycling --> minimal CSA change, increase in strength Weight training, sprint training --> increase in muscle CSA, increase in strength Combination training, kayaking --> increase in muscle CSA, hypertrophy Combination training --> increase hyperplasia in rats, could not get same change in humans, no increase in number of muscle cells following birth Myostatin Transforming growth factors (TGF-beta) member Negative regulator of muscle growth Inhibits myogensis: muscle growth and differentiation Double-muscling phenotype is a heritable condition Mutations lead to significantly more muscle mass hence stronger than normal Antibodies developed to neutralise myostatin, may be used therapeutically in treating muscle washing or gene doping Muscle Strain Muscle Tendon junction Excessive stretching while loading give predisposition to muscle strain

5 BIOL1900 Page 9 4. Articular System Thursday, 12 March :31 am Joint Component Joint is any place where two or more bones meet. Do not have to move with respect to one another Joint components Bones (2 or more) Cartilage (tendons) Ligaments (capsules) Tendons (muscles) Physical Activity Adaptations Immobilization No impact loading Size decreases Mechanically weaker Swimming No impact loading No change in size/ strength Moderate Activity Endurance running Size increase Mechanically stronger Extensors/ flexors differ Time period of months High Intensity Initial response Size decrease/ no change 6 weeks Adaptive response Increased size/ strength 6/12 months Physical Activity Cartilage Joint Function Immovable (synarthrisis) Slightly moveable (amphiarthrisis) Freely moveable (diarthrisis - synovial) Joint range of motion Limiting factors restricting the range of motion in the joint Capsule and ligaments 47% Muscle Fasea 41% Tendons 10% Skin 2%

6 BIOL1900 Page 19 measurement technuiques It is now recognised as an applied branch of developmental biology called auxology Auxology cuts across many other fields of study including animal science, paediatrics, genetics, obstetrics, orthodontics, nutrition studies, human movement studies etc. We use Auxology within HMND Studies to: Monitor body changes to ensure the optimal growth and development of all children Evaluate growth for the purpose of encouraging the health and vigour of children and adults over the life span It is an axiom of paediatrics that a healthy childhood lifestyle provides a strong basis for adult health By modifying factors that predispose a child to marginal health, both the child and resultant grown adult will benefit Maternal Smoking and Birth Weight Babies born to smoking mothers weigh on average 170g less than babies born to non-smoking mothers Neonatal mortality is 28% higher Relative Age Effect (RAE) Successful athletes more likely to be born ealier in the selection year Relative age: Difference in chronoligcal age between children in a single group RAE: Consequences of relative age Children born at the start of the year may be more advance in growth and development than other children born at the end of the year

7 BIOL1900 Page 21 Growth Spurt During the adolescent growth spurt, under the control of the endocrine system, whole combinations of maturity events take place all of which are interrelated and occur in sequence, although timing is highly variable For instance: Somatic development The spurt in height, lean, strength etc. is very much tied in with sexual development, the appearance of secondary sex characteristics, menarche etc. Human Endocrine System Hypothalamus = commander; regulates Pituitary gland, releases: Human growth hormone (HgH) Trophic Growth hormones: regulate other endocrine glands that influence adolescent growth changes Changes in Age with Serum Testosterone Changes in age with serum Estradiol Blood levels of HGH in boys

8 BIOL1900 Page 22 Timing of Events Measurement of Maturity Status Development of pre-pubertal childhood state to mature adult state is often evaluated in terms of '4 aproaches' 1. Somatic characteristics 2. Sexual development 3. Skeletal development 4. Dental development Skeletal (bone) Age Hand-Wrist X-rays: left hand and wrist (RUS) 27 bones in the and wrist Score/rate the ossification of the epiphyseal regions (growth plates/ end plates) to a healthy 'normative cohort' There are 3 different techniques for determining skeletal age 1. Tanner Whitehouse method: (UK) takes the mean of individually rated bones 2. Greulich-Pyle (US): uses an atlas for comparison (lacks sensitivity) 3. Roche (Fels) (US) Classified as normal if within 2 years of chronological age Dental Age: Demirjian System Basis: uses the eruption or non-eruption of teeth in the same way as the appearance and ossification in bones

9 BIOL1900 Page Growth and Development 3 Wednesday, 17 June 2015 Crude prediction of Adult height and weight Males/ Boys 2 x height at age 2 years = adult height 5 x weight at age 2 years = adult weight Females/ girls 2 x height at age 18 months = adult height 5 x weight at age 18 months = adult weight Growth in height and weight until onset of puberty Height - 2-6cm/year Weight 2.5kg/year Adolescent Growth Spurt Boys Add 20kg Add 20cm Girls Add 16cm Add 16kg 5:05 pm Why, on average are males taller than females Magnitude of growth spurt is 2cm/year greater in boys On average, boys have 2 years more of pre-adolescent growth than girls (~5cm/yr for 2yrs) Girls stop growing ~age 16 Boys continue until ~age 18 Affect of Gender on Growth and Health Patterns For a similar chronological age, girls are always closer to maturity than boys Girls are more resistant than boys to influences that might deflect them from their normal growth pattern They are also easier to rehabilitate For almost all disease states, mortality is lower in women Life expectancy greater in women Overall, xx chromosome is healthier than xy combination Gender Differences in Structural Growth Patterns Small structural differences between boys and girls untill the adolescent growth spurt Sexual dimorphism - phenotypic changes Estimated lean muscle mass in growing Girls and Boys