BLOOD SUPPLY OF THE LUXGS 



245 



are directed toward the pleura, and their apices toward the root 

 of the lung. In many of the lower mammals these lobules are 

 more distinctly outlined by interlobular connective tissue than is 

 the case in man. 



At its apex a small bronchiole enters the pulmonary lobule 

 and divides into its terminal bronchioles. At the same point 

 a terminal branch of the pulmonary artery enters with the bron- 

 chiole and supplies the anas- 

 tomosing capillary plexus in 

 the alveolar walls. Branches 

 of the bronchial artery do 

 not supply any of the intra- 

 lobular structures, and the 

 pulmonary veins which re- 

 turn the blood from- the al- 

 veolar capillaries arise at the 

 periphery of the lobule and 

 immediately enter the inter- 

 lobular connective tissue. 



The interlobular connec- 

 tive tissue contains the small- 

 er branches of the pulmonary 

 veins, the lymphatics return- 

 ing from the pleura, and the 

 non-medullated nerve trunks 

 which are destined for the 

 supply of the pleura and 

 the intralobular pulmonary 

 tissue. 



BLOOD SUPPLY OF THE LUNGS. The blood supply of the 

 lungs is derived from two distinct sources, the pulmonary arteries 

 and the bronchial arteries. The former is destined chiefly for 

 aeration in the capillaries of the alveolar walls, the latter for the 

 nutrition of the bronchial walls. 



The pulmonary artery enters at the hilum in company with the 

 vein and the bronchus. It follows the bronchus throughout its 

 course and gives an arterial branch to each of its subdivisions. 

 The large arteries nearly equal in size the bronchus in relation to 

 which they lie, but the smaller branches are not more than one- 

 fourth to one-fifth the diameter of their bronchus. Throughout 

 their course the branches of the pulmonary arteries lie on the wall 



FlG. 208. DlAGllAM OF A LOBULE OF THE 

 LUNG. 



A, atrium ; B, terminal bronchiole ; (7, 

 pulmonary alveolus ; P, alveolar duct ; <S, air 

 sac ; F, infundibulum. The artery is striped, 

 the vein open. (After Miller.) 



