Barbara Meyrick

A reconstruction of the duct system and secretory tubules of the human bronchial submucosal gland.

A graphic reconstruction has been made of a submucosal gland from a normal human main bronchus, revealing a collecting duct not previously described. Ciliated respiratory epithelium dips into the gland opening to line the first part of the duct, the ciliated duct, and then gives way, in the collecting duct, to an epithelium composed of tall, columnar, eosinophilic cells containing numerous large mitochondria. This cell structure suggests that the collecting duct controls ionic and water concentration. From the collecting duct arise secretory tubules lined by mucous cells—mucous tubules. Tubules lined by serous cells—serous tubules—arise from mucous tubules either terminally or laterally.

The alveolar brush cell in rat lung—a third pneumonocyte

In the rat alveolar lining epithelium a third cell type has been found which resembles the brush cell previously described in large airways in rat and in man. It is here reported in rat intrapulmonary airways of all sizes. The brush cell is characterized by blunt, squat microvilli on its free edge, bundles of fine filaments throughout its cytoplasm, and the presence of β-glycogen. In the alveolus its free edge is restricted by cytoplasmic flanges from adjacent type I pneumonocytes. It is found centrally and distally within the acinus and comprises 5–10% of pneumonocytes if the count is based on alveolar lining cells whose nuclei are included in the section. Its function may be absorptive or that of a stretch or chemoreceptor.

Nerves in rat intra-acinar alveoli: an electron microscopic study.

Abstract Unmyelinated axons in a Schwann cell sheath have been found in the rat lung, in alveolar wall deep within the acinus: they are rare. These fibres may be sensory, their position suggesting an association with the J receptor. Processes from the alveolar pericyte are commonly seen; these resemble an axon in that they contain numerous tubules similar in diameter to neurotubules and are found within a basement membrane.

Smooth muscle myosin in precursor and mature smooth muscle cells in normal pulmonary arteries and the effect of hypoxia

Exposure to hypoxia increases pulmonary arterial muscularity-in the intra-acinar arteries new muscle appears in the normally nonmuscular regions and in the preacinar arteries, medial thickness increases. In the present study by immunofluorescence techniques, the myosin content of the pulmonary arterial walls at two levels of the circulation (intra-acinar and preacinar) were studied in control rats and those exposed to hypobaric hypoxia of 380 torr for 3,7, 10, or 14 days. In control animals, we show that the precursor smooth muscle cells, pericytes and intermediate cells normally present in the nonmuscular regions of the intra-acinar arteries, contain smooth muscle myosin. With exposure to hypoxia, smooth muscle myosin in the intra-acinar arteries increases to Day 10, both in area of staining and fluorescent intensity. This is in contrast to the preacinar arteries were only the area of myosin increases. Antihuman platelet (non-muscle) myosin shows a little faint staining in both control and hypoxic animals. Adaptations to hypoxia by the intra-acinar precursor and preacinar mature smooth muscle cells is different, and suggests that the functions subserved by the myosin filaments at each of the two levels differs.

The Effect of Chronic Hypoxia on Pulmonary Arteries in Young Rats

The effect of hypoxia on the postnatal development of rat lung from 8 days of life and continuing for 3, 7, 14, 21 and 28 days is described, with particular emphasis on the pulmonary arterial circulation. In hypoxic rats, absolute lung volume and body weight increases more slowly than in age-matched controls but lung volume relative to body weight is greater. After three days hypoxia intra-acinar arterial concentration is reduced and medial thickness of small arteries increased but by Day 7, both features return to normal values. By Day 14, right ventricular hypertrophy is apparent as is reduction in lumen diameter of preacinar arteries. From Day 21, muscle is seen in smaller and more peripheral arteries than normal: By Day 28 arteries of all sizes show increased medial thickness, and arterial and alveolar concentration is reduced. Compared with adult rats the growing lung seems to be somewhat protected in that the hypoxia-induced changes occur slowly although ultimately their severity is similar. At the end of the exposure period, however, the young lung is small for age suggesting that the changes are more severe than in the adult.

The alveolar wall

DURING the last quarter of a century much has been learnt of the structure of the alveolar wall. The two outstanding discoveries are the detection of a surface-tension-reducing substance in the alveolus and the identification of its continuous epithelial lining. The light microscope was used to examine the lung by Malpighi (I6281694 ) in the second half of the 17th century: he and Leeuwenhoek (I 632-I 723) saw the capillaries whose presence had hitherto only been assumed by men such as Harvey (I578-I657) who believed that blood flowed in one direction through the lungs. The possibility of a continuous epithelial lining was long the subject of a controversy (see Macklin I938, 1954; Miller 1947; von Hayek 1960) which was settled in 1952 by Low and Daniels using the additional resolution of the electron microscope. The continuous epithelial lining was shown by Policard in 1954 to include two different cell types. This article deals only with aspects of alveolar wall structure and does not discuss alveolar configuration or arrangement.

MICROCIRCULATION: DEFINITION AND ORGANIZATION AT TISSUE LEVEL

The microcirculation of an organ can be defined in a variety of ways-some based on structure, some on function. The definition of microcirculation used here reflects structural features peculiar to the lung. Certainly the microcirculation includes capillaries, the smallest units or segments. The capillary bed, in fact, offers one way to define microcirculation. Consideration of gas exchange, however, extends the definition to include precapillary vessels, since, by direct observation through a thoracic window in the cat, Staub has observed gas exchange in arteries up to 100 pm in diameter. Since gas exchange is doubtless the most important feature of the circulation, another possibility is to include all vessels within the respiratory unit-the acinus. (The acinus is composed of all lung beyond the terminal bronchiolus and includes the alveoli opening onto the respiratory bronchioli and the alveolar ducts, and those beyond.) Vessels, whether artery or vein, proximal to the end of the terminal bronchiolus then can be considered preacinar, and those within the respiratory unit as intraacinar. This is a convenient way to landmark vascular structures and will be used for that purpose here. As a definition of microcirculation. we offer one whose scale is broader than capillary and smaller than the acinus.

Primary pulmonary hypertension a case report including electronmicroscopic study

Abstract This case report of primary pulmonary hypertension includes descriptions of clinical, light and, for the first time, electron microscopic features. The electron microscope revealed an increase in thickness of the endothelial cell and basement membrane in alveolar (non-muscular) vessels, that is, an increase in thickness of the blood/gas barrier. Pinocytic vesicles were increased in endothelial cells of both muscular and non-muscular vessels. Capillary lumen blockage by endothelial cells, and an onion-like lesion, recently described with the light microscope by Anderson et al. (1973a) corresponded with the ultra-structural appearance of whorling due to an increase in basement membrane, pericytes, elastic tissue and collagen around a capillary. The resulting reduction in the number of small blood vessels correlated with a low transfer factor: other pulmonary function tests were normal.

1207 STRUCTURAL FEATURES OF CONTINUED HYPOXIA ON LARGE PULMONARY ARTERIES OF RAT

Hypoxia produces muscularization of the peripheral normally non-muscular regions of pulmonary artery. In addition, medial thickening is found in the large already muscular arteries and is known to be associated, in certain congenital heart diseases, with narrowing of internal lumen diameter.The present study traces the development of increased wall thickness in the muscular pulmonary artery at the hilum, seen in rats with hypoxia-induced pulmonary hypertension. Hypertension was produced by exposure to half an atmosphere for 1-52 days. For this study, arteries and airways were distended and fixed with glutaraldehyde using a simultaneous injection technique. All coats of the pulmonary artery are affected. The first change is apparent from Day 3, hypertrophy of endothelial cells and adventitial fibroblasts with increased connective tissue, all leading to thickening of the coats. By Day 7, the medial coat also is increased, due at first to hypertrophy of smooth muscle cells and later to increased connective tissue. Uptake of 3H-thymidine shows an early and marked increase in mitotic activity of fibroblasts and endothelial cells but smooth muscle cells show little increase. On removal from hypoxia, wall thickness decreases but lumen diameter does not increase.