The structure of the interalveolar septum of the mammalian lung

Abstract

Abstract Light and electron microscopic examination of serial transverse sections of interalveolar septa of hamster lung have demonstrated a virtually continuous connective tissue sheet of variable thickness in the interalveolar septum. This central sheet, like connective tissue elsewhere, is composed of ground substance in which are immersed cells, collagen and elastin. A capillary network lies on each surface of this sheet. The capillary basement membrane is continuous with the central sheet but in contrast to it is thin, uniform and devoid of cells, collagen or elastin. Capillaries on one surface frequently anastomose directly through the septum with capillaries on the opposite surface. The central sheet is shown to be virtually continuous despite frequent thinning. Whenever cells, collagen or elastin occur in the interalveolar septum, it is always in the central sheet. The efficiency of this arrangement in combining optimum gas conductance with adequate mechanical support is pointed out. The central sheet is also continuous with the perivascular connective tissue cuff and thus may serve as an important route of extracellular fluid transport to the perivascular lymphatics.