Scanning Electron Microscopic Observations of the Human Respiratory Tract Martha F. Greenwood, MD,
Phillip Holland,
As viewed by scanning electron microscopy, the luminal surface of the human trachea at 12 weeks' gestation shows a predominance of microvillous-covered, nonciliated cells, in contrast to the heavily ciliated tracheobronchial surface seen at 34 weeks' gestation. Hyaline membrane disease produces a confluent lining material in the lung periphery that obscures the bronchiolar and alveolar surface architecture. Large saucershaped alveoli, numerous alveolar pores, and an abundance of in situ alveolar macrophages are observed in chronic bronchitis and in emphysematous lungs. The scanning electron microscope offers an additional tool for the study of developmental and pathological processes in the human respiratory tract.
In
recent years, scanning elec¬ tron microscopy has found wide
application in the microanatomic in¬ vestigation of a variety of cells and organ tissues. It is possible to rapidly characterize vast surface areas and to determine cellular orientation and ul¬ trastructural detail in a three-dimen¬ sional perspective. Previous scanning electron microscopic observations of Received for
cepted Aug 20.
publication May 28, 1974;
ac-
From the Department of Pediatrics, University of Kentucky School of Medicine, Lexington. Reprint requests to Department of Pediatrics, University of Kentucky School of Medicine, 800 Rose St, Lexington, KY 40506 (Dr. Greenwood).
MD
the
respiratory tract in a number of species have indicated the usefulness of this instrument in the investiga¬
tion of the normal tracheobronchial and pulmonary parenchymal surface and the alveolar macrophage re¬ sponse to foreign stimuli.18 The pur¬ pose of the present report is to de¬ scribe the developmental surface changes in the respiratory tract at 12 and 34 weeks' gestation and the pathological alterations induced by hyaline membrane disease, chronic bronchitis, and emphysema, using scanning electron microscopy. MATERIALS AND METHODS
Specimens were obtained from human fetuses following therapeutic abortion, from premature infants with fatal hyaline membrane disease, and from adults with chronic bronchitis and emphysema who un¬ derwent lobectomy for squamous cell carci¬ noma of the lung. Lung tissue uninvolved with neoplasm was examined. The pulmo¬ nary tissue was fixed immediately follow¬ ing surgical excision or pronouncement of death. The trachea or a bronchus was cannulated with a polyethylene catheter and the specimens were lavaged three times with buffered saline solution, pH 7.4, con¬ taining heparin, 25 units/ml, for the re¬ moval of mucus and surface debris. Fol¬ lowing lavage, 2.5% glutaraldehyde in 0.1M sodium cacodylate buffer, pH 7.4, contain¬ ing 0.2% magnesium chloride was injected intratracheally or intrabronchially to in¬ flate the lungs so that the serosal lung sur-
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opposed the rib cage as observed through the incised diaphragm or until the surgically excised lobe was completely ex¬ panded. The catheter was clamped and the pulmonary tissue was immersed in 2.5% glutaraldehyde for two hours at 4 C (39 F). Sections of pulmonary tissue were cut measuring approximately 2 mm in thick¬ face
ness
and 8
mm
in their greatest diameter
following fixation in glutaraldehyde. The tissue was then prepared as previously de¬ scribed.2 After attachment to aluminum stubs, the specimens were coated with gold-palladium in a vacuum evaporator to a thickness of approximately 200 Ang¬ stroms and examined at 20 kv with a stereoscan microscope. Measurements were made directly from the photomicro¬ graphs and converted to microns with a magnification scale.
RESULTS
Respiratory Tract
at 12 Weeks' Gestation
Nonciliated cells studded with sur¬ face microvillous projections are prominent on the luminal surface of the trachea of the human fetus at 12 weeks' gestation (Fig 1, top left). Cili¬ ated cells are evenly distributed among the nonciliated cells and gen¬
erally appear singly, although groups of three to four are occasionally seen. Aggregates of small surface projec¬ tions that represent developing lung parenchyma are observed in the im¬ mature lung at this early gestational age (Fig 1, top right).
Tracheobronchial Surface at 34 Weeks' Gestation Ciliated cells cover the luminal sur¬ face of the trachea in the human pre¬ mature infant at 34 weeks' gestation (Fig 1, bottom left). The ciliated cells are rarely interrupted by nonciliated cells, which are partially concealed by overlying cilia. The cilia are uni¬ form in diameter and length, approxi¬ mately 0.2µ and 6.5µ to 7.0µ, respec¬
tively. The main stem bronchi are also heavily ciliated, yet groups of microvillous-covered, nonciliated cells are occasionally observed. The length of microvilli is extremely varied in in¬
dividual luminal cells of the main stem bronchus, allowing identifica¬ tion of the cell-to-cell junctions (Fig 1, bottom right).
Pulmonary Parenchyma in Hyaline Membrane Disease of Infancy Generalized atelectasis with alveo¬ lar septal thickening, characteristic of hyaline membrane disease, is read¬ ily identified by scanning the pulmo¬ nary parenchyma at low magnifica¬ tion (Fig 2, top left). At higher magnification, the normal bronchiolar and alveolar architecture is obscured by a uniformly distributed, firmly ad¬ herent, homogeneous lining material that was not removed by pulmonary lavage (Fig 2, top right and bottom left). Capillary alveolar networks, al¬ veolar pores, or free pulmonary phago¬ cytes could not be recognized in nu¬ merous specimens examined.
Pulmonary Parenchyma in Chronic Bronchitis and Emphysema
Large, saucer-shaped alveoli, nu¬ alveolar pores of varying size,
merous
and an abundance of free cells are ob¬ served in a representative low-power micrograph of the pulmonary paren¬ chyma in chronic bronchitis and em¬ physema (Fig 2, bottom right). The surface topography and the ruffled plasma membrane of alveolar macro¬ phages are seen in a higher-power
micrograph of
a
single alveolus (Fig
3, top left). The free alveolar
scav¬
enger cells appear singly or in clus¬ ters on the alveolar wall and are fre¬
observed within the alveolar The density and spatial rela¬ pores. tionship of the microvillous-covered type II alveolar cells to the rela¬ tive smooth-surfaced type I simple squamous cells in an alveolus from a patient with emphysema are seen in Fig 3 (top right). The biconcave shape and compression of the erythrocytes as they traverse the alveolar capil¬ laries are recognized through the thin layer of epithelial cells and the endo¬ thelial lining cells of blood vessels. Stubby microvilli cover the surfac¬ tant-secreting type II alveolar cell, and multiple surface excretory pores are present as seen in Fig 3 (bottom left). A cluster of in situ alveo¬ lar macrophages in a patient with chronic bronchitis is seen in Fig 3 (bottom right). The plasma mem¬ branes of these cells are ruffled in un¬ dulating waves of activity, and the trailing pseudopod of one cell is seen at the right of the micrograph.
quently
COMMENT In recent years the scanning elec¬ microscope has offered an addi¬ tional tool for investigation of tissue topography and cell surface ultrastructure. The scanning electron pho¬ tomicrograph image is the result of secondary electrons emitted from the tissue as the electron beam scans the specimen surface. Since scanning electron microscopy does not depend on light passing through the speci¬ men, thin sections of biologic mate¬ rial are not required. A further ad¬ vantage of this instrument is a wide magnification range that allows rela¬ tively vast areas of tissue to be scanned rapidly, following which ul¬ trastructural examination of specific areas of interest can be carried out. The cellular orientation, relative distribution of the varied cell types, and surface topography of the human respiratory tract have been difficult to tron
Downloaded From: http://archpedi.jamanetwork.com/ by a New York University User on 06/23/2015
define clearly by either light or trans¬ mission electron microscopy. How¬ ever, previous studies have indicated that the surface of the normal res¬ piratory tract may be clearly defined, using scanning electron microscopy.1-8 Cilia have been observed by light microscopy in the human trachea by 10 weeks' gestation9; however, the cel¬ lular detail of the tracheobronchial surface at this early stage of develop¬ ment has remained difficult to ascer¬ tain from sectioned material. The spatial relationship and ratio of cili¬ ated to microvillous-covered cells throughout the trachéal surface at 12 weeks' gestation are readily deter¬
mined, using scanning microscopy.
Ciliated cells are randomly inter¬ spersed with microvillous-covered cells, and the ratio of ciliated to non¬ ciliated cells is approximately 1:3. The
distribution and ratio of ciliated to nonciliated cells in the human trachea at 12 weeks' gestation is similar to that in the normal adult mouse trachea where nonciliated cells are predominant.2 In contrast, the human tracheobronchial surface at 34 weeks' gestation is covered almost exclu¬ sively with ciliated cells and is similar to the adult monkey trachea where nonciliated cells are rarely visible from surface observations.3 Large, saucer-shaped pulmonary al¬ veoli interrupted by numerous alveo¬ lar pores and an abundance of free alveolar phagocytes are character¬ istically seen in human adults with chronic bronchitis and emphysema. Alveolar macrophages were fre¬ quently observed in clusters on the alveolar wall and within the alveo¬ lar pores. The phagocyte-to-phagocyte adhesiveness within the alveolar lu¬ men was also observed in monkeys given Calmette-Guérin bacillus but not in controls.3 Ruffling of the plasma membrane is characteristic of in situ monocytes and alveolar macro¬ phages. The surface topography of these cells clearly differs from the rel¬ atively smooth surface of the thymusderiyed lymphocyte and the elon-
Fig 1.—Top left, Luminal surface of trachea in 12-week-old human fetus, with ciliated and microvillous-covered cells (original magnifi¬ cation 6,810). Top right, Pulmonary parenchyma from 12-weekold human fetus. Peripheral airways are seen in cross section, and surface projections represent developing lung parenchyma (original magnification 390). Bottom left, Luminal surface of trachea in
34-week-old human infant. Ciliated cells are predominant (original magnification 4,500). Bottom right, Main stem bronchus from 34-week-old premature infant. Ciliated cells are interrupted by non¬ ciliated cells covered by microvilli of varying lengths (original magni¬ fication 2,750).
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Fig 2.—Top left, Low magnification of lung parenchyma affected by hyaline membrane disease. Note alveolar septal thickening (orig¬ inal magnification 130). Top right, Peripheral airway in hyaline membrane disease. Erythrocytes are enmeshed in thick lining mem¬ brane (original magnification 1,220). Bottom left, Higher magni¬ fication of peripheral airway in hyaline membrane disease. Con-
fluent membrane obscures underlying cell structure (original magnification x 2,420). Bottom right, Pulmonary parenchyma from adult with chronic bronchitis and emphysema. Note large saucershaped alveoli, numerous alveolar pores (AP), and abundance of free macrophages (M) (original magnification 350).
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Fig 3.—Top left, Higher magnification of alveolus from same Groups of alveolar macrophages (M) are numerous (original magnification 1,580). Top right, Pulmonary alveolus from adult with emphysema, with erythrocytes (E) traversing alveolar capil¬ laries and microvillous-covered type II alveolar cells (II) (original magnification 1,700). Bottom left, Higher magnification of type II adult.
alveolar cell. Note cell surface openings and numerous short microvillous projections (original magnification 9,640). Bottom right, Cluster of alveolar macrophages in alveolus of adult with chronic bronchitis. Note ruffled plasma membranes and trailing extension of cell at right (original magnification 4,120).
Downloaded From: http://archpedi.jamanetwork.com/ by a New York University User on 06/23/2015
gated microvillous projections of the bone marrow-derived lymphocyte sur¬ face described by Polliack et al.10 The distinctive surface morphologi¬
cal characteristics of the two alveolar wall cell types are clearly defined by looking into an alveolus with the scanning electron microscope. The relatively smooth surface of the simple squamous epithelial cell or type I alveolar cell contrasts with the microvillous-covered surface of the type II alveolar cell. Macklin11 origi¬ nally suggested that the type II al-
source of pulmo¬ and cytoplasmic lamellar bodies have been identified in this cell by transmission electron microscopy. The microvilli of the hu¬ man type II alveolar cell are stubby and evenly distributed over the lumi¬ nal surface. Numerous luminal pore openings are interspersed among the microvilli. The presence of short mi¬ crovilli on the surface of this cell has been previously verified in the mouse,2 rat,6 horse,7 and monkey.3 The morphological observations
veolar cell nary
was
the
surfactant,
made in this study indicate that scanning electron microscopy is a val¬ uable technique for the ultrastruc¬ tural investigation of human respira¬ tory tract development and disease. Future studies correlating light, transmission, and scanning micros¬ copy in a variety of pathological states in the respiratory tract appear indicated. This investigation was supported by Kentucky Tobacco and Health Research Institute grant 026.
References 1. Barber VC, Boyde A: Scanning electron microscopic studies of cilia. Z Zellforsch Mikrosk Anat 84:269-284, 1968. 2. Greenwood MF, Holland P: The mammalian respiratory tract surface: A scanning electron microscopic study. Lab Invest 27:296-304, 1972. 3. Greenwood MF, Holland P: Scanning electron microscopy of the normal and BCG-stimulated primate respiratory tract.
J Reticuloendothel Soc 13:183-192, 1973. 4. Groniowski J, Walski M, Biczysko W: Application of scanning electron microscopy for studies of lung parenchyma. J Ul-
trastruct Res
38:473-481, 1972. 5. Holma B: Scanning electron microscopic observation of particles deposited in the lung. Arch Environ Health 18:330-339, 1969. 6. Kuhn C III, Finke EH: The topography of the pulmonary alveolus: Scanning electron microscopy using different fixations. J Ultrastruct Res 38:161-173, 1972. 7. Nowell JA, Tyler WS: Scanning electron microscopy of the surface morphology of mammalian lungs. Am Rev Respir Dis 103:313-328, 1971.
Ecology of Coronary
8. Wang NS, Thurlbeck WM: Scanning electron microscopy of the lung. Hum Pathol 1:227-231, 1970. 9. Bucher U, Reid L: Development of the mucus-secreting elements of the human lung. Thorax 16:219-225, 1961. 10. Polliack A, Lampen N, Clarkson BD, et al: Identification of human B and T lymphocytes by scanning electron microscopy. J Exp Med 138:607-624, 1973. 11. Macklin CC: The pulmonary alveolar mucoid film and the pneumonocytes. Lancet 266:1099-1104, 1954.
Disease*
"Modern man in industrial society is an animal which, shortly after maturation, is confined to a system of special cages, in one of which, a mobile steel and plastic cage, he is exposed for one or two hours daily to complex decisions, frustration and danger, in an atmosphere high in carbon monoxide, while transported to and from other cages. In other cages, under constant temperature environments, the animal's physical activity is strictly constrained to many hours of sitting and a few moments daily of standing, with short, level walks, all of very low energy expenditure. The industrialized species of man is habitually overfed with animal and grain chow which usually includes 20 per cent of all calories from saturated fats, 20 per cent from refined carbohydrates, and 10 per cent from fermented spirits, plus varying concentrations of herbicides, pesticides, hormones, antibiotics, oxidizing agents, and radioactive isotopes. Man is systematically conditioned to self-administer 20 potent doses of nicotine, and five of caffeine alkaloids daily. He is also trained to lie motionless in a darkened cage for three hours and watch a cathode ray tube which continuously presents ambiguous information and repeated suggestions for unhygienic, purposeless activity. He is rewarded to the degree that he pursues this goal-less activity during the day." •From Blackburn H: 169.
1974,
Controversy, in Ingelfinger FJ, et al: Internal Medicine. Philadelphia, WB Saunders Co,
Downloaded From: http://archpedi.jamanetwork.com/ by a New York University User on 06/23/2015
Phillip Holland,
As viewed by scanning electron microscopy, the luminal surface of the human trachea at 12 weeks' gestation shows a predominance of microvillous-covered, nonciliated cells, in contrast to the heavily ciliated tracheobronchial surface seen at 34 weeks' gestation. Hyaline membrane disease produces a confluent lining material in the lung periphery that obscures the bronchiolar and alveolar surface architecture. Large saucershaped alveoli, numerous alveolar pores, and an abundance of in situ alveolar macrophages are observed in chronic bronchitis and in emphysematous lungs. The scanning electron microscope offers an additional tool for the study of developmental and pathological processes in the human respiratory tract.
In
recent years, scanning elec¬ tron microscopy has found wide
application in the microanatomic in¬ vestigation of a variety of cells and organ tissues. It is possible to rapidly characterize vast surface areas and to determine cellular orientation and ul¬ trastructural detail in a three-dimen¬ sional perspective. Previous scanning electron microscopic observations of Received for
cepted Aug 20.
publication May 28, 1974;
ac-
From the Department of Pediatrics, University of Kentucky School of Medicine, Lexington. Reprint requests to Department of Pediatrics, University of Kentucky School of Medicine, 800 Rose St, Lexington, KY 40506 (Dr. Greenwood).
MD
the
respiratory tract in a number of species have indicated the usefulness of this instrument in the investiga¬
tion of the normal tracheobronchial and pulmonary parenchymal surface and the alveolar macrophage re¬ sponse to foreign stimuli.18 The pur¬ pose of the present report is to de¬ scribe the developmental surface changes in the respiratory tract at 12 and 34 weeks' gestation and the pathological alterations induced by hyaline membrane disease, chronic bronchitis, and emphysema, using scanning electron microscopy. MATERIALS AND METHODS
Specimens were obtained from human fetuses following therapeutic abortion, from premature infants with fatal hyaline membrane disease, and from adults with chronic bronchitis and emphysema who un¬ derwent lobectomy for squamous cell carci¬ noma of the lung. Lung tissue uninvolved with neoplasm was examined. The pulmo¬ nary tissue was fixed immediately follow¬ ing surgical excision or pronouncement of death. The trachea or a bronchus was cannulated with a polyethylene catheter and the specimens were lavaged three times with buffered saline solution, pH 7.4, con¬ taining heparin, 25 units/ml, for the re¬ moval of mucus and surface debris. Fol¬ lowing lavage, 2.5% glutaraldehyde in 0.1M sodium cacodylate buffer, pH 7.4, contain¬ ing 0.2% magnesium chloride was injected intratracheally or intrabronchially to in¬ flate the lungs so that the serosal lung sur-
Downloaded From: http://archpedi.jamanetwork.com/ by a New York University User on 06/23/2015
opposed the rib cage as observed through the incised diaphragm or until the surgically excised lobe was completely ex¬ panded. The catheter was clamped and the pulmonary tissue was immersed in 2.5% glutaraldehyde for two hours at 4 C (39 F). Sections of pulmonary tissue were cut measuring approximately 2 mm in thick¬ face
ness
and 8
mm
in their greatest diameter
following fixation in glutaraldehyde. The tissue was then prepared as previously de¬ scribed.2 After attachment to aluminum stubs, the specimens were coated with gold-palladium in a vacuum evaporator to a thickness of approximately 200 Ang¬ stroms and examined at 20 kv with a stereoscan microscope. Measurements were made directly from the photomicro¬ graphs and converted to microns with a magnification scale.
RESULTS
Respiratory Tract
at 12 Weeks' Gestation
Nonciliated cells studded with sur¬ face microvillous projections are prominent on the luminal surface of the trachea of the human fetus at 12 weeks' gestation (Fig 1, top left). Cili¬ ated cells are evenly distributed among the nonciliated cells and gen¬
erally appear singly, although groups of three to four are occasionally seen. Aggregates of small surface projec¬ tions that represent developing lung parenchyma are observed in the im¬ mature lung at this early gestational age (Fig 1, top right).
Tracheobronchial Surface at 34 Weeks' Gestation Ciliated cells cover the luminal sur¬ face of the trachea in the human pre¬ mature infant at 34 weeks' gestation (Fig 1, bottom left). The ciliated cells are rarely interrupted by nonciliated cells, which are partially concealed by overlying cilia. The cilia are uni¬ form in diameter and length, approxi¬ mately 0.2µ and 6.5µ to 7.0µ, respec¬
tively. The main stem bronchi are also heavily ciliated, yet groups of microvillous-covered, nonciliated cells are occasionally observed. The length of microvilli is extremely varied in in¬
dividual luminal cells of the main stem bronchus, allowing identifica¬ tion of the cell-to-cell junctions (Fig 1, bottom right).
Pulmonary Parenchyma in Hyaline Membrane Disease of Infancy Generalized atelectasis with alveo¬ lar septal thickening, characteristic of hyaline membrane disease, is read¬ ily identified by scanning the pulmo¬ nary parenchyma at low magnifica¬ tion (Fig 2, top left). At higher magnification, the normal bronchiolar and alveolar architecture is obscured by a uniformly distributed, firmly ad¬ herent, homogeneous lining material that was not removed by pulmonary lavage (Fig 2, top right and bottom left). Capillary alveolar networks, al¬ veolar pores, or free pulmonary phago¬ cytes could not be recognized in nu¬ merous specimens examined.
Pulmonary Parenchyma in Chronic Bronchitis and Emphysema
Large, saucer-shaped alveoli, nu¬ alveolar pores of varying size,
merous
and an abundance of free cells are ob¬ served in a representative low-power micrograph of the pulmonary paren¬ chyma in chronic bronchitis and em¬ physema (Fig 2, bottom right). The surface topography and the ruffled plasma membrane of alveolar macro¬ phages are seen in a higher-power
micrograph of
a
single alveolus (Fig
3, top left). The free alveolar
scav¬
enger cells appear singly or in clus¬ ters on the alveolar wall and are fre¬
observed within the alveolar The density and spatial rela¬ pores. tionship of the microvillous-covered type II alveolar cells to the rela¬ tive smooth-surfaced type I simple squamous cells in an alveolus from a patient with emphysema are seen in Fig 3 (top right). The biconcave shape and compression of the erythrocytes as they traverse the alveolar capil¬ laries are recognized through the thin layer of epithelial cells and the endo¬ thelial lining cells of blood vessels. Stubby microvilli cover the surfac¬ tant-secreting type II alveolar cell, and multiple surface excretory pores are present as seen in Fig 3 (bottom left). A cluster of in situ alveo¬ lar macrophages in a patient with chronic bronchitis is seen in Fig 3 (bottom right). The plasma mem¬ branes of these cells are ruffled in un¬ dulating waves of activity, and the trailing pseudopod of one cell is seen at the right of the micrograph.
quently
COMMENT In recent years the scanning elec¬ microscope has offered an addi¬ tional tool for investigation of tissue topography and cell surface ultrastructure. The scanning electron pho¬ tomicrograph image is the result of secondary electrons emitted from the tissue as the electron beam scans the specimen surface. Since scanning electron microscopy does not depend on light passing through the speci¬ men, thin sections of biologic mate¬ rial are not required. A further ad¬ vantage of this instrument is a wide magnification range that allows rela¬ tively vast areas of tissue to be scanned rapidly, following which ul¬ trastructural examination of specific areas of interest can be carried out. The cellular orientation, relative distribution of the varied cell types, and surface topography of the human respiratory tract have been difficult to tron
Downloaded From: http://archpedi.jamanetwork.com/ by a New York University User on 06/23/2015
define clearly by either light or trans¬ mission electron microscopy. How¬ ever, previous studies have indicated that the surface of the normal res¬ piratory tract may be clearly defined, using scanning electron microscopy.1-8 Cilia have been observed by light microscopy in the human trachea by 10 weeks' gestation9; however, the cel¬ lular detail of the tracheobronchial surface at this early stage of develop¬ ment has remained difficult to ascer¬ tain from sectioned material. The spatial relationship and ratio of cili¬ ated to microvillous-covered cells throughout the trachéal surface at 12 weeks' gestation are readily deter¬
mined, using scanning microscopy.
Ciliated cells are randomly inter¬ spersed with microvillous-covered cells, and the ratio of ciliated to non¬ ciliated cells is approximately 1:3. The
distribution and ratio of ciliated to nonciliated cells in the human trachea at 12 weeks' gestation is similar to that in the normal adult mouse trachea where nonciliated cells are predominant.2 In contrast, the human tracheobronchial surface at 34 weeks' gestation is covered almost exclu¬ sively with ciliated cells and is similar to the adult monkey trachea where nonciliated cells are rarely visible from surface observations.3 Large, saucer-shaped pulmonary al¬ veoli interrupted by numerous alveo¬ lar pores and an abundance of free alveolar phagocytes are character¬ istically seen in human adults with chronic bronchitis and emphysema. Alveolar macrophages were fre¬ quently observed in clusters on the alveolar wall and within the alveo¬ lar pores. The phagocyte-to-phagocyte adhesiveness within the alveolar lu¬ men was also observed in monkeys given Calmette-Guérin bacillus but not in controls.3 Ruffling of the plasma membrane is characteristic of in situ monocytes and alveolar macro¬ phages. The surface topography of these cells clearly differs from the rel¬ atively smooth surface of the thymusderiyed lymphocyte and the elon-
Fig 1.—Top left, Luminal surface of trachea in 12-week-old human fetus, with ciliated and microvillous-covered cells (original magnifi¬ cation 6,810). Top right, Pulmonary parenchyma from 12-weekold human fetus. Peripheral airways are seen in cross section, and surface projections represent developing lung parenchyma (original magnification 390). Bottom left, Luminal surface of trachea in
34-week-old human infant. Ciliated cells are predominant (original magnification 4,500). Bottom right, Main stem bronchus from 34-week-old premature infant. Ciliated cells are interrupted by non¬ ciliated cells covered by microvilli of varying lengths (original magni¬ fication 2,750).
Downloaded From: http://archpedi.jamanetwork.com/ by a New York University User on 06/23/2015
Fig 2.—Top left, Low magnification of lung parenchyma affected by hyaline membrane disease. Note alveolar septal thickening (orig¬ inal magnification 130). Top right, Peripheral airway in hyaline membrane disease. Erythrocytes are enmeshed in thick lining mem¬ brane (original magnification 1,220). Bottom left, Higher magni¬ fication of peripheral airway in hyaline membrane disease. Con-
fluent membrane obscures underlying cell structure (original magnification x 2,420). Bottom right, Pulmonary parenchyma from adult with chronic bronchitis and emphysema. Note large saucershaped alveoli, numerous alveolar pores (AP), and abundance of free macrophages (M) (original magnification 350).
Downloaded From: http://archpedi.jamanetwork.com/ by a New York University User on 06/23/2015
Fig 3.—Top left, Higher magnification of alveolus from same Groups of alveolar macrophages (M) are numerous (original magnification 1,580). Top right, Pulmonary alveolus from adult with emphysema, with erythrocytes (E) traversing alveolar capil¬ laries and microvillous-covered type II alveolar cells (II) (original magnification 1,700). Bottom left, Higher magnification of type II adult.
alveolar cell. Note cell surface openings and numerous short microvillous projections (original magnification 9,640). Bottom right, Cluster of alveolar macrophages in alveolus of adult with chronic bronchitis. Note ruffled plasma membranes and trailing extension of cell at right (original magnification 4,120).
Downloaded From: http://archpedi.jamanetwork.com/ by a New York University User on 06/23/2015
gated microvillous projections of the bone marrow-derived lymphocyte sur¬ face described by Polliack et al.10 The distinctive surface morphologi¬
cal characteristics of the two alveolar wall cell types are clearly defined by looking into an alveolus with the scanning electron microscope. The relatively smooth surface of the simple squamous epithelial cell or type I alveolar cell contrasts with the microvillous-covered surface of the type II alveolar cell. Macklin11 origi¬ nally suggested that the type II al-
source of pulmo¬ and cytoplasmic lamellar bodies have been identified in this cell by transmission electron microscopy. The microvilli of the hu¬ man type II alveolar cell are stubby and evenly distributed over the lumi¬ nal surface. Numerous luminal pore openings are interspersed among the microvilli. The presence of short mi¬ crovilli on the surface of this cell has been previously verified in the mouse,2 rat,6 horse,7 and monkey.3 The morphological observations
veolar cell nary
was
the
surfactant,
made in this study indicate that scanning electron microscopy is a val¬ uable technique for the ultrastruc¬ tural investigation of human respira¬ tory tract development and disease. Future studies correlating light, transmission, and scanning micros¬ copy in a variety of pathological states in the respiratory tract appear indicated. This investigation was supported by Kentucky Tobacco and Health Research Institute grant 026.
References 1. Barber VC, Boyde A: Scanning electron microscopic studies of cilia. Z Zellforsch Mikrosk Anat 84:269-284, 1968. 2. Greenwood MF, Holland P: The mammalian respiratory tract surface: A scanning electron microscopic study. Lab Invest 27:296-304, 1972. 3. Greenwood MF, Holland P: Scanning electron microscopy of the normal and BCG-stimulated primate respiratory tract.
J Reticuloendothel Soc 13:183-192, 1973. 4. Groniowski J, Walski M, Biczysko W: Application of scanning electron microscopy for studies of lung parenchyma. J Ul-
trastruct Res
38:473-481, 1972. 5. Holma B: Scanning electron microscopic observation of particles deposited in the lung. Arch Environ Health 18:330-339, 1969. 6. Kuhn C III, Finke EH: The topography of the pulmonary alveolus: Scanning electron microscopy using different fixations. J Ultrastruct Res 38:161-173, 1972. 7. Nowell JA, Tyler WS: Scanning electron microscopy of the surface morphology of mammalian lungs. Am Rev Respir Dis 103:313-328, 1971.
Ecology of Coronary
8. Wang NS, Thurlbeck WM: Scanning electron microscopy of the lung. Hum Pathol 1:227-231, 1970. 9. Bucher U, Reid L: Development of the mucus-secreting elements of the human lung. Thorax 16:219-225, 1961. 10. Polliack A, Lampen N, Clarkson BD, et al: Identification of human B and T lymphocytes by scanning electron microscopy. J Exp Med 138:607-624, 1973. 11. Macklin CC: The pulmonary alveolar mucoid film and the pneumonocytes. Lancet 266:1099-1104, 1954.
Disease*
"Modern man in industrial society is an animal which, shortly after maturation, is confined to a system of special cages, in one of which, a mobile steel and plastic cage, he is exposed for one or two hours daily to complex decisions, frustration and danger, in an atmosphere high in carbon monoxide, while transported to and from other cages. In other cages, under constant temperature environments, the animal's physical activity is strictly constrained to many hours of sitting and a few moments daily of standing, with short, level walks, all of very low energy expenditure. The industrialized species of man is habitually overfed with animal and grain chow which usually includes 20 per cent of all calories from saturated fats, 20 per cent from refined carbohydrates, and 10 per cent from fermented spirits, plus varying concentrations of herbicides, pesticides, hormones, antibiotics, oxidizing agents, and radioactive isotopes. Man is systematically conditioned to self-administer 20 potent doses of nicotine, and five of caffeine alkaloids daily. He is also trained to lie motionless in a darkened cage for three hours and watch a cathode ray tube which continuously presents ambiguous information and repeated suggestions for unhygienic, purposeless activity. He is rewarded to the degree that he pursues this goal-less activity during the day." •From Blackburn H: 169.
1974,
Controversy, in Ingelfinger FJ, et al: Internal Medicine. Philadelphia, WB Saunders Co,
Downloaded From: http://archpedi.jamanetwork.com/ by a New York University User on 06/23/2015
