LYMPHATICS IN THE LUNG OF A PRECOCIAL BIRD BEFORE AND AFTER HATCHING

Abstract

A light and electron microscopic study of pulmonary lymphatics was carried out in quailembryos (embryonic day; ED 13-17), completed with samples of lungs of quail 90 min, 24 hafter hatching and two 2-day-old and three adult quail. The aim of the study was to depict themorphology of pulmonary lymphatics by determining the dynamics in ontogeny and toestablish the rules of their distribution. The primitive lymphatics appear on ED 13 and 14 asclosed thin-walled tubes in abundant interparabronchial mesenchyme. They seeminglydifferentiate from the mesenchymal cells. Due to the proliferation, growth, and enlargement ofthe parabronchial compartments, the interparabronchial septa disappear to a large extent,and the external walls of parabronchi appose and join. On ED 16 and 17, the mesenchyme issqueezed to the trigonal fields among the neighboring parabronchi. The lymphatics formbroad, voluminous lakes around the arteries; on the other hand, they are also found in closecontact with the gas exchange tissue as juxta-air capillary lymphatics. After hatching, theformer interparabronchial septa disappear, and the imaginary boundary betweenparabronchi is demarcated by interparabronchial arteries and veins. The lymphatics areconfined to the adventitial connective tissue which conducts the larger arteries and veins ofthe original trigone of the interparabronchial septa. The richly vascularized parabronchi inmature quail are poor in connective tissue and to a large extent devoid of lymphatics, incomparison to the mammalian lung where the lymphatic capillaries have their roots at thelevel of the respiratory bronchioles.The avian pulmonary lymphatics serve as an appropriate model for the analysis ofprinciples controlling the origin and distribution of lymphatics in general.