Anatomical and functional differences between the alveolar and extraalveolar interstitium are discussed. The extraalveolar interstitium can accomodate active changes of caliber of the blood vessels and large amounts of edematous fluid; accordingly, the connective tissue is loose and distensible. Alveolar interstitium is in contact with capillaries and has very little distensibility because of attachments between endothelium and epithelium; accordingly it can accomodate only small pockets of fluid. Functionally with lung inflation, alveolar capillaries are compressed whereas extraalveolar vessels passively expand showing a radically different behavior of both compartments. Between both compartments, 'boundary cells' are seen which in the extraalveolar interstitium form the first lymphatics. On the basis of these observations, it is postulated that alveolar capillaries only exchange fluid (normal or edematous) with the alveolar interstitium, while normal lymph and perivascular edematous cuffs originate locally in the extra-alveolar interstitium. The branching nature and large size of the extraalveolar sheaths makes it difficult to identify the precise height of leakage sites.
|Number of pages||14|
|State||Published - 1981|