PP20 Pre and Postnatal Muscle Development 2

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PP20Pre and Postnatal Muscle Development 2

• Chapter 5 pg 77-101
• ANS 3043
• University of Florida
• Dr. Michael J. Fields

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Myogenesis (continued)

• Muscle Fiber Development
• Occurs during first two thirds of prenatal
  development
• Almost completed before birth (some postnatal
  development)
• Species dependent and possibly related to state
  of maturity
• Pig myofiber numbers established 90-95 days
  post-conception
• Myofiber numbers do not change in postnatal
  period

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Myogenesis (continued)

• Mechanisms for increasing muscle fiber number
• Prenatal (only significant period when muscle
  fiber number can be increased)
• Hyperplasia is significant
• Hypertrophy is minimal
• Postnatal
• Hyperplasia is minimal
• Increase in muscle fiber number during this
  period is attributed to lengthening of partial
  fibers
• Satellite cells may contribute to increased fiber
  number during muscle regeneration (activated to
  proliferate and fuse with other satellite cells
  to form new fibers)
• Hypertrophy is significant

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Muscle Fibers

• Factors Affecting Muscle Fiber Development
• Animal Variation
• Muscle fiber number is quite variable for animals
  within and between species
• Muscles within an animal
• Muscles exist in numerous sizes and shapes
• Eye few thousand fibers
• Semimembranosus of hind leg several billion
  fibers

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Muscle Fibers

• Species
• Differences in body size is related to number of
  muscle fibers (i.e. increased muscle mass between
  elephant and mouse due to increased muscle
  fibers)
• Excess growth in muscle diameter is not favorable
  from a metabolic standpoint
• Diffusion of nutrients and metabolites in and out
  of a muscle fiber is restricted if radial growth
  of fiber is excessive

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Muscle Fibers

• Nutrition
• Greater impact on muscle at some stages of growth
  than others
• Can alter muscle number only during prenatal
  period
• Severe nutrient restriction dramatically
  suppresses muscle fiber formation resulting in
  runt pigs at birth (failure of secondary muscle
  fiber development during gestation)
• If runts survive they become fatter with less
  muscle than litter mates
• Postnatal depravation has little effect on muscle
  fiber number

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Muscle Fibers

• Age
• Number of muscle fibers is fixed at birth and
  does not usually change with age
• Age related changes only occur in utero and only
  during early and mid pregnancy
• Most mammals and avian species are determinant
  growers reach a specific mature size provided
  adequate nutrition

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Muscle Fibers

• Fish are indeterminate growers no predetermined
  mature size
• Grow to a size reflective of nutrients in their
  environment
• Capable of generating new fibers after hatching,
  which contributes significantly to overall
  hypertrophy of muscle

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Muscle Fibers

• Senescence process of growing old
• Muscle is not completely regenerated (fewer
  satellite cells)
• Protein degradation gt Protein synthesis
• Results in loss of muscle mass and muscle fiber
  number
• Not relevant in meat-producing animals, but
  apparent in breeding stock and companion animals
  that reach older ages
• Cause is unclear but possibly associated with
  losses of neuronal input
• Associated with muscle wasting in elderly humans
• Use it or lose it principle