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Animal Phys L3

QuestionAnswer
Embryo germ layers ectoderm mesoderm endoderm
Ectoderm outer layer (forms skin and nervous tissue)
Mesoderm middle layer (forms skin and nervous tissue)
Endoderm inner layer (forms internal organs and linings)
Differentiation process where one cell becomes more specialised
Progenitor cells early founder/precursor cells that give rise to specific tissues
Mesenchyme embryonic connective tissue containing multipoint cells that can form muscle, bone and fat
Skeletal muscle cell myofibril large, multinucleate cell achieves size through fusion of many myoblasts during development
what does multinucleation support? high metabolic and protein synthesis demand
Muscle life cycle: Postnatal ongoing myoblast differentiation and limited growth
Muscle life cycle: Adulthood homeostasis; hypertrophy occurs with exercise or anabolic signals
Muscle life cycle: Geriatric muscle loss (sarcopenia) - decline in mass and function
Myoblasts progenitor cels of muscle fibres; unipotent (only form muscle)
Embryonic myoblasts originate from mesenchyme
postnatal myoblasts arise from satellite cells, which lie dormant beside mature fibres (under basal lamina)
Satellite cells "reserve" myoblasts for repair and regeneration
Hyperplasia increase in fibre number (mainly during embryonic/foetal/neonatal stages) driven by proliferation and fusion of myoblasts
what is hyperplasia controlled by? Myogenic Regulatory Factors (MRFs) - transcription factors that regulate myogenesis
Gene consists of Open reading frame Promoter region
Open reading frame (ORF) the protein coding region of the gene
Promoter region the site where transcription begins in the gene
Transcription factors (TFs) bind to specific DNA sequences (response elements) in the promoter region to activate transcription
Myf5 expressed earliest, initiates myoblast formation
MyoD expressed during growth and repair stages marks commitment of cells to muscle lineage
Myogenin expressed during myotube formation drives differentiation and fusion of myoblasts into myotubes
MRF4 highly expressed in adult muscle maintains muscle phenotype in mature fibres
MRFs act together to: regulate precursor proliferation activate muscle-specific genes promote sarcomere assembly and fibre differentiation
waves of myotube formation primary, secondary and tertiary myotubes
Primary myotubes Embryonic first wave; establish muscle positions and scaffold structure
Secondary myotubes Foetal form along the scaffolding of primary myotubes
Tertiary myotubes Neonatal, only in some species Add additional fibres postnatally
Sarcomere basic contractile unit formed after myoblast fusion
Developmental myosin temporary structural proteins that help form and stabilise early sarcomeres later replaced by adult myosin isoforms as fibres mature
How does timing of formation affect fibre type? Early developing fibres (embryonic): Postural muscles Late-developing fibres (foetal): locomotor muscles
Hypertrophy Increase in fibre size, not number
Hypertrophy is driven by... increases synthesis of myofibrillar proteins Assembly of proteins into new sarcomeres peripheral displacement of nuclei
Where do satellite cells reside? between the sarcolemma and basal lamina they remain quiescent until injury
What do satellite cells do upon activation? Upon activation (eg damage, Training), they re enter the cell cycle to form new myoblasts for repair, not normal growth
Mature fibres show low MRF expression minimal turnover of myonuclei postnatal growth = hypertrophy only
Dominant MRFs for growth and repair MyoD, Myogenin eg, satellite cell activation
Dominant MRFs for hypertrophy Myogenin, MRF4 eg, Myofibrillar protein synthesis
Double muscling gene causes increased muscle fibre number (hyperplasia) is a mutation
Callipyge gene postnatal hypertrophy via epigenetic regulation of muscle genes mutation
Created by: sakelleher29
 

 



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