Muscle growth - General Principles of Muscle Growth Growth...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: General Principles of Muscle Growth Growth Anabolism Protein Synthesis Hypertrophy What’s Unique About Muscle Cells? • Multiple nuclei Hyperplasia to Hypertrophy • The number of skeletal muscle nuclei is The directly related to myofiber size & may directly related ultimately limit the amount of protein present in the fiber. present ∀ ↑ in nuclei (or DNA) gives skeletal in muscle more capacity to synthesize & maintain protein. maintain • Thus, an ↑ in nuclei is a prerequisite for Thus, post-natal muscle growth post-natal Skeletal Muscle Protein is Dynamic • 20 – 25% can be broken down & replaced 20 each day (early in life) each • 1 – 2% later in life Growth Terminology • Synthesis – Conversion of amino acids to proteins. – Transcription of RNA from DNA – Translation of mRNA forming a Translation polypeptide polypeptide Growth Terminology • Degradation – Proteolysis of polypeptides by Proteolysis proteinases proteinases • Cathepsins • Calpains – Sometimes referred to as breakdown Sometimes breakdown Growth Terminology • Growth – Protein accumulation or accretion – Protein synthesis (PS) > Protein degradation (PD) Growth Terminology • Turnover – Nonspecific term combining PS & PD – Sometimes referred to as breakdown Sometimes breakdown – More specifically referred to metabolism More metabolism Hypertrophy • Muscle fiber number set at birth. Muscle fiber ∀ ↑ myofibril number. myo Hypertrophy • Myofibrils split longitudinally. • Occurs when: – myofibrils reach a critical size. – force production reaches a specific magnitude. Hypertrophy: splitting myofibrils • Splitting allows the SR Splitting and T-tubules to infiltrate the myofibrillar assembly. assembly. • May provide peripheral May cites where new actin and myosin filaments can be deposited. can Quantification of Hypertrophy • Total DNA content – Indicates muscle cell number • Total protein/DNA ratio – Indicates muscle cell size • Quantity of muscle fiber protein supported Quantity by one nucleus by – DNA unit Fractional Rates ∀ ↑ Synthesis rate &(or) attenuating breakdown rate are currently perceived as major approaches to enhance lean tissue accretion. accretion. • Growth occurs by increasing protein Growth deposited OR deposited • Decrease breakdown Protein Synthesis Synthesis Protein Protein Accretion Accretion Protein Protein Degradation Degradation Suppression of Protein Secretion • Nutrient limitation Nutrient – protein, energy, key protein, minerals minerals • Stress hormones – Glucocorticoids Suppression of Accretion • Breakdown remains at its original Breakdown level for a time when synthesis is depressed in muscle. depressed – Results in a net catabolic state. Results catabolic – Breakdown declines in an adaptive manner to Breakdown minimize tissue (protein) loss. minimize • Only in stressful situations may Only breakdown increase in muscle tissue. breakdown – High glucocorticoids, injury, sepsis. Factors influencing protein accretion • Age – Decrease satellite cell incorporation – Decrease protein synthesis – Increase protein degradation/turnover Factors influencing protein accretion • Dietary Energy – Myofiber growth relative to development Myofiber stage – Priority • Nervous tissue • Skeletal tissue growth • Muscle Muscle • Fat – Cannot inhibit fat deposition w/out interfering with Cannot muscle growth muscle Factors influencing protein accretion • Sex – Males have greater protein accretion Males than females. than Factors influencing protein accretion • Genetic Selection – Actually select for ↑ number not ↑ size Actually – Perhaps selection for “white” fibers (?) Factors influencing protein accretion • Exercise – Function dependent ∀↑ number of ribosomes number ∀↑ quantity of RNA quantity ∀↑ RNA polymerase RNA ∀↓ protein catabolism protein ...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online