Capillary Cross-sectional Area Research Articles

Capillary supply and cross-sectional area of slow and fast twitch muscle fibres in man.

The muscles triceps brachii, quadriceps femoris (part vastus lateralis) and soleus were analysed in 6 men and 6 women for fibre composition (% slow twitch, ST-fibres and % fast twitch, FT-fibres), fibre cross sectional areas, and capillarization. Also the fraction of fibres enclosed by their own fibre type was analysed together with the capillary supply of these fibres. Fibre composition was 39(19-60)% ST in m. triceps brachii, 60(29-78)% ST in m. vastus lateralis and 73(49-88)% ST in m. soleus. Fibre areas ranged from 2,320 to 16,667 microns2 being smallest in m. triceps brachii and largest in m. soleus (p less than 0.05) and with ST fibres being significantly smaller than FT fibres in some of the muscles. In all muscles the shape of the fibres was elliptical with the larger diameter being about twice the smaller diameter. Capillary density per cross sectional muscle area was not related to the fibre composition and was 379(302-500) cap/mm2 in m. triceps brachii, 404(284-529) cap/mm2 in m. vastus lateralis and 417(333-592) cap/mm2 in m. soleus. However, capillary supply expressed as fibre type area per capillary was up to 40% larger for FT-fibres than for ST-fibres within the same muscle (p less than 0.05). The capillary supply of enclosed fibres was not different from that of fibres surrounded also by the other fibre type. The results demonstrate that the difference in capillary supply to ST and FT-fibres is less distinct in humans than in other mammals, which is consistent with the metabolic potentials also being more alike.

STUDIES ON THE FORM OF THE AMPHIBIAN RED BLOOD CELL

1. A mercury drop in contact with a cylindrical surface takes the form of a flat elliptical disc. Increasing the volume of the drop causes an increase in the area and eccentricity of the drop but causes no appreciable increase in thickness. With constant drop volume, the larger the cylinder the less eccentric the fluid drop.2. Analyses of blood cell form and capillary diameter in Triturus and Pleurodeles disclosed the following relationships. The red cell is circular if its area does not exceed that of the capillary. Eccentricity increases first in a curvilinear and then in a linear fashion as the red cell increases beyond the cross-sectional area of the capillary. Under conditions of essentially constant red cell area, eccentricity is inversely related to the cross-sectional area of the capillary.3. Based on the experimental findings the following equation may be derived relating red cell area, capillary cross-sectional areas and eccentricity (a/b):[See the Equation in the PDF]4. Evidence for the physical nature of the red cell was discussed in relation to the model system.