Capillary-to-fiber geometry and mitochondrial density in hummingbird flight muscle

Respir Physiol. 1992 Jul;89(1):113-32. doi: 10.1016/0034-5687(92)90075-8.


We investigated structural characteristics for high O2 flux in hummingbird flight muscle, i.e. the most O2 demanding skeletal muscle per unit tissue mass among vertebrates. Pectoralis and supracoracoideus muscles of 3-4 g hummingbirds (Selaphorus rufus) were perfusion fixed in situ, processed for electron microscopy and analyzed by morphometry. Small fiber size (group mean +/- SE, 201 +/- 14 microns 2 at 2.1 microns sarcomere length), large capillary length per fiber volume (8947 +/- 869 mm-2) and high mitochondrial volume density per volume of muscle fiber (34.5 +/- 0.9%) were characteristic features of the muscles. Considering capillary supply and mitochondrial volume on an individual fiber basis showed that the size of the capillary-to-fiber interface (i.e. capillary surface per fiber surface) was also high in the muscles. Comparison with mammalian hindlimb pointed to a major role of the size of the capillary-to-fiber interface in providing a great potential for O2 flux rate from capillary to muscle fiber mitochondria in hummingbird flight muscle.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Birds / anatomy & histology*
  • Birds / metabolism
  • Capillaries / anatomy & histology
  • Female
  • Flight, Animal* / physiology
  • Male
  • Mitochondria, Muscle / metabolism
  • Mitochondria, Muscle / ultrastructure
  • Muscles / blood supply*
  • Muscles / metabolism
  • Muscles / ultrastructure
  • Oxygen Consumption