The tracheobronchial epithelium of the bonnet monkey (Macaca radiata): a quantitative ultrastructural study

Histochemical and ultrastructural observations of respiratory epithelium and gland in yak (Bos grunniens)

Submucous glands and epithelial mucous cells of yak (Bos grunniens) respiratory tract have been studied by a variety of histochemical methods and transmission electron microscopy for differentiating and characterizing serous and mucous cells. By light microscopy, the distribution, numbers of mucous cells, volume of mucous glands (Reid index), and the ratio of mucous cell to serous cell in the bronchial tree were measured with different staining. Histochemically, a majority of mucous cells, presented in the surface epithelium of bronchi and glands, secreted neutral and acid mucosubstances, only a few sulfated mucosubstances were present. No mucus-producing cells were observed from the terminal to respiratory bronchiolar level. Ultrastructurally, serous cells in glands of the lamina propria had two distinct forms: one type filled with many round dense secretory granules, plentiful RER and few other organelles, similar to other animals; the other type contained some oval mitochondrial and distended RER, the granules resembled the former. The mucous cells in gland were similar to that of epithelium, which containing abundant secretory granules with an eccentric core. The mucous cells of the surface epithelium differ from other animals in the structure and histochemistry of their secretory granules. Analysis of the size and distribution of the secretory granules and other organelles of serous cells suggested that differences represent different phases of a secretory cycle, not various populations of cell or granules.

Postnatal lung development of rhesus monkey airways: cellular expression of Clara cell secretory protein

Clara cell secretory protein (CCSP) is a protective lung protein that is believed to have antioxidant, immunomodulatory, and anticarcinogenic properties. Evidence suggests that CCSP is involved in mitigating many lung disease states during development including asthma. This study's rationale is to define the distribution and abundance of CCSP in the airway epithelium of the rhesus monkey during postnatal lung development using carefully controlled site-specific morphometric approaches in defined airway regions. Immunoreactive CCSP was found in nonciliated cells and mucous cells, including glands, throughout the airway epithelium at all ages, with proximal and mid-level airways having the highest labeling. Overall airway CCSP levels were low at 1 week and 1 month, doubled between 1 and 3 months, and changed little from 3 months to 3 years. Thus, the critical developmental window for CCSP expression to reach adult levels in the rhesus conducting airways occurs between 1 and 3 months of age.

Light and electron microscopic studies of the trachea in the one-humped camel (Camelus dromedarius)

Histology of trachea of camel (Camelus dromedarius) was studied using light, scanning (SEM) and transmission electron microscopy (TEM). Tissue samples taken from the trachea (proximal, middle and distal part) were routinely prepared for histology (LM, EM) and stained with haematoxylin and eosin, Van Giesson (VG), Alcian blue, Periodic acid schiff (PAS), Masson's trichrome (MT), Verhof, PAS-VG and PAS-MT. The trachea of camel consists of 66-75 incomplete cartilaginous rings of hyaline. The lamina epithelium is composed of pseudostratified-ciliated columnar epithelium with many goblet cells. Submucosal layers were loose connective tissue with many elastic fibres. The mucosal and submucosal layers were 517.2 +/- 61.6 microm (n = 20) thick. Submucosal glands were tubuloalveolar with mucous (acidic and neutral) secretions. Trachealis muscle was attached to the inside sheet of tracheal cartilage. Ultrastructural studies showed that surface epithelium is pseudostratified with mucus-producing goblet cells, ciliated and basal cells, similar to other mammals. The ciliated cells contained many mitochondria, oval nucleus and many big granules. In scanning electron microscopy (SEM) studies, viscoelastic layers were observed on the epithelial surface of trachea, and there were highly condensed cilia under this layer.

An SEM study of the morphology of the lower respiratory-tract surface of the reindeer (Rangifer tarandus tarandus L.)

The morphological features of the surface of the lower respiratory tract (trachea, bronchus, bronchiolus, distal airways, and alveoli) from 10 reindeer (Rangifer tarandus tarandus L.), differing in age and sex, were studied using scanning-electron microscopy. The respiratory surface of the reindeer generally resembles that reported previously in similar studies for other mammalian species. Ciliated epithelial cells, goblet cells, microvillous cells, Clara cells, alveolar epithelial cells of type 1 and type 2, and alveolar macrophages could be distinguished by their universally characteristic surface morphologies. The rarity of Kohn pores in the alveolar walls of reindeer was considered to be the most striking difference in comparison to most other species.

Direct gene transfer of human CFTR into human bronchial epithelia of xenografts with E1-deleted adenoviruses

We describe the use of a human bronchial xenograft model for studying the efficiency and biology of in vivo gene transfer into human bronchial epithelia with recombinant E1 deleted adenoviruses. All cell types in the surface epithelium except basal cells efficiently expressed the adenoviral transduced recombinant genes, lacZ and CFTR, for 3-5 weeks. Stable transgene expression was associated with high level expression of the early adenoviral gene, E2a, in a subset of transgene expressing cells and virtually undetectable expression of the late adenoviral genes encoding the structural proteins, hexon and fiber. These studies begin to address important issues that relate to safety and in vivo efficacy of recombinant adenoviruses for gene delivery into the human airway.

Epithelial strips: an alternative technique for examining arachidonate metabolism in equine tracheal epithelium

We have developed an alternative method for examining equine tracheal epithelial arachidonic acid (AA) metabolism that utilizes strips of pseudostratified columnar epithelium attached to a layer of elastic tissue 80 to 130 microns thick. We compared the responses of this preparation with those of enzymatically dispersed suspensions of tracheal epithelium obtained from the same animal. Strips incubated with [3H]AA incorporated 40.8 +/- 3.6% of added radioactivity and released 2.55 +/- 0.23% of incorporated radioactivity when stimulated with 5 microM A23187. Values for the cell suspension were 59.6 +/- 1.6% and 1.90 +/- 0.08%, respectively. Stimulation with 50 microM histamine or bradykinin resulted in significant release of free [3H]AA only from the strips. High-performance liquid chromatography radioactivity profiles of eicosanoids released following stimulation with 5 microM A23187 demonstrated peaks that coeluted with free AA, prostaglandin (PG) E2, and PGF2 alpha for the strips, and free AA, leukotriene B4, and 5-HETE for the cell suspensions. The absence of PGE2 production by cell suspensions was confirmed by assaying immunoreactive PGE2 in supernatants from unlabeled strips and suspensions stimulated with 5 microM A23187. Epithelial strips produced 10.3 +/- 1.3 ng PGE2/ml supernatant, whereas 5 x 10(6) cells in suspension produced less than 100 pg/ml. Despite the lack of PG production by the cell suspensions, immunocytochemical staining with an anti-PGH synthase antibody demonstrated the presence of PGH synthase in epithelial cells of both preparations. These data indicate that, in contrast to epithelial cell suspensions, epithelial strips synthesize cyclooxygenase metabolites and respond to peptide agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphometric assessment of pulmonary toxicity in the rodent lung

An overview of the epithelial and interstitial composition of rat respiratory airways shows complexity and variability. Airway epithelium varies in 1) different airway levels; 2) the types and ultrastructure of cells present; and 3) the abundance, type, and composition of stored secretory product. Unbiased sampling of airways is done using airway microdissection with a specific binary numbering system for airway generation. Vertical sections of selected airways are used to sample epithelium and interstitium. We determine the ratios of the volume of epithelial or interstitial cells to the total epithelial or interstitial volume (Vv). The surface of the epithelial basal lamina to the total epithelial or interstitial volume (Sv) is determined using point and intersection counting with a cycloid grid. Using the selector method on serial plastic sections, we determine the number of epithelial or interstitial cells per volume (Nv) of total epithelium or interstitium. We calculate the number of epithelial or interstitial cells per surface of epithelial basal lamina (Ns) by dividing Nv by Sv where the volumes are the same compartment. We calculate average cell volumes (v) for specific epithelial and interstitial cells by dividing the absolute nuclear volume by the ratio of the nucleus to cell volume (Vv). By multiplying the average cell volume (v) by the ratio of organellar volume to cell volume (Vv), we calculate the average organellar volume per cell. These unbiased stereological approaches are critical in a quantitative evaluation of toxicological injury of rat tracheobronchial airways.

An ultrastructural study of the equine lower respiratory tract

The surface features of the lower respiratory tract of 20 clinically normal horses of different ages and types were studied with scanning electron microscopy. Parallel light microscopical and transmission electron microscopical studies were also carried out. The ciliary carpet was virtually complete from the trachea to the lobar bronchi. In small bronchi, ciliation was less complete allowing numerous non-ciliated mucous cells to become obvious. The terminal bronchioles, populated mainly by non-ciliated bronchiolar epithelial cells, had an abrupt junction with alveolar ducts. Interalveolar pores were common particularly in older horses.

Characterization of guinea pig tracheal epithelial cells maintained in biphasic organotypic culture: cellular composition and biochemical analysis of released glycoconjugates

An air-liquid interface (biphasic) primary culture system in which guinea pig tracheal epithelial cells maintain morphologic characteristics of differentiated epithelium has been developed in this laboratory. In this report, we compared quantitatively cell populations of 8-day cultures to those of epithelial mucosa in intact trachea. In addition, high molecular weight glycoconjugates released by the cultured cells were isolated and characterized. Quantitative morphometric analysis revealed similar volume densities of ciliated, secretory, basal, and "other" cells in cultures and in intact tracheal surface epithelium, although the cultures tended to have smaller cells and contained fewer basal cells. High molecular weight glycoconjugates released apically by cell cultures and excluded from Sepharose CL-4B columns contained approximately 5% hyaluronic acid but undetectable amounts of other proteoglycans, such as chondroitin sulfate, heparan sulfate, and dermatan sulfate. The hyaluronidase-resistant glycoconjugates exhibited a peak buoyant density at 1.49 g/ml on cesium chloride density gradient centrifugation and were shown to contain mucin-type carbohydrate to peptide linkages (i.e., GalNAc to ser/thr) and an amino acid composition typical of respiratory mucins. The results indicate that this organotypic cell culture system mimics quite closely morphology of mucosal epithelium in intact airways and that the cells release high molecular weight glycoconjugates with biochemical properties of mucin-type glycoproteins. Thus, this in vitro system appears well-suited for studies of mucin secretion and other functions of respiratory epithelial cells.

The role of basal cells in attachment of columnar cells to the basal lamina of the trachea

The mechanism by which basal cells play a role in attachment of airway epithelium to the basal lamina has not been determined. Our hypothesis is that basal cells form a structural bridge between columnar cells and the basal lamina via hemidesmosomes, the cytoskeleton, and desmosomes. To evaluate this hypothesis, we determined the percentage of the columnar cell surface area associated with attachment to the basal lamina and the basal cell in tracheal epithelia of different heights. Tracheas from mice, hamsters, rats, bonnet monkeys, cats, and sheep were prepared for electron microscopy by standard techniques. The height of the epithelia ranged from 8.6 microns in the hamster to 56.8 microns in the sheep. The number of basal cells/100 microns ranged from 3.4 in the hamster to 21.4 in the sheep. The percentage of the basal lamina covered by basal cells increased from 32.6 in the hamster to 94.7 in the sheep. In the shorter epithelia of the hamster, 32% of the columnar cell attachment to the basal lamina was indirect through basal cells, and in the taller epithelia of the sheep, 92% of the columnar cell attachment was by this means. Conversely, the percentage of columnar cell surface in contact with the basal lamina decreased from 67.4% in the hamster to 5.3% in the sheep. These data demonstrate that basal cells play a role in attachment of columnar epithelium to the basal lamina by presenting a surface area for cell-to-cell attachment, thus acting as a bridge between columnar cells and the basal lamina.

Cell distribution in tracheal surface epithelium and the effects of long-term pilocarpine and atropine administration

Cell distribution and the effects of 12 daily injections of 80 mg/kg pilocarpine or 5 mg/kg atropine were studied in rat tracheal epithelium. Ciliated, periodic-acid-Schiff-positive (PAS+), Alcian blue-positive (AB+), nonstaining, and basal cells were counted and their order of occurrence was recorded. Pilocarpine caused a decrease in ciliated and an increase in PAS+, basal, and nonstaining cell numbers. Atropine caused similar changes, although to a much lesser extent. AB+ cells were rare. Cell occurrence was randomized by computer, and comparisons with nonrandomized counts were made to discern between 1) differences in cell arrangement owed to variations in cell numbers, and 2) actual biases in cell distribution. In general, ciliated areas amounted to a few cells and were separated by nonciliated patches of comparable size. The grouping characteristics of cells supported the notion that basal cells were surrounded by their progeny and that daughter cells were displaced by siblings. It was concluded that the cells were not randomly distributed. Basal cells were dispersed, and probably immediately related to PAS+ cells but not to ciliated cells. A bias toward grouping implied concurrent differentiation of clusters of sibling cells. With drug treatment, a substantial increase in PAS+ cells without increase in cell concentration suggested a decrease in ciliated cell differentiation. Larger groups of secretory cells with treatment suggested cell division without differentiation through the basal cell pathway. Cholinergic agents were not the predominant modulators of this epithelium, and their effect was probably secondary to influence over mucociliary function.

Lectin-detectable effects of localized pneumonia on airway mucous cell populations: role of cyclooxygenase metabolites

We examined the airway secretory apparatus of adult sheep with experimental pneumonia to look for morphologic and lectin-binding correlates of increased mucus production. The animals were inoculated in the right caudal lobar bronchus either with starch broth containing Pasteurella haemolytica (INF, n = 6), starch broth alone (SHAM, n = 6), or with P. haemolytica and subsequently treated (INF/T, n = 5) with 2 mg/kg indomethacin, subcutaneously three times daily for 6 days. In the INF and INF/T groups, a localized pneumonic infiltrate containing P. haemolytica organisms was present. The bronchi (18-23rd generation) adjacent to the pneumonic lesion had an increased gland volume fraction (6.3 +/- 3.7% in INF, 11.3 +/- 2.4% in INF/T, and 3.1 +/- 1.9% in SHAM, p less than 0.05 among the three). The mean population densities of BSA-reactive (identifying alpha-D-gal) cells were 41.9 +/- 2.7% in the INF, 40.1 +/- 5.6% in the INF/T, versus 14.3 +/- 1.5% in the SHAM group (p less than 0.05), while the corresponding values for PNA-reactive [identifying beta-D-gal(1----3)-D-galNAc] cells were 28.8 +/- 5.1%, 0%, and 0%, respectively. Nor morphologic abnormalities were seen in the trachea, but BSA staining was shifted to morphologically different mucous cells in the INF and INF/T. We conclude that in localized P. haemolytica pneumonia in sheep (1) there are morphologic changes of the airway secretory apparatus adjacent to the lesion, (2) the glycoconjugate profile of secretory cells adjacent to and remote from the lesion is altered, and (3) cyclooxygenase products influence the chemical composition of secretory cells.

Tracheobronchial epithelium in the adult rhesus monkey: a quantitative histochemical and ultrastructural study

Previous studies of the intrapulmonary conducting airways of sheep and rabbit have demonstrated marked diversity in the epithelial populations lining them. Because studies of trachea and centriacinar regions of macaque monkeys suggested that primates may be even more diverse, the present study was designed to characterize the epithelial population throughout the airway tree of one primate species, the rhesus monkey. Trachea and intrapulmonary airways of the right cranial and middle lobes of glutaraldehyde/paraformaldehyde-infused lungs of five adult rhesus monkeys were microdissected following the axial pathway. Each branch was assigned a binary number indicating its specific location within the tree. The trachea and six generations of intrapulmonary airway from the right cranial lobe were evaluated for ultrastructure and quantitative histology as were those of the right middle lobe for quantitative carbohydrate histochemistry. Four cell types were identified throughout the tree: ciliated, mucous goblet, small mucous granule, and basal. The tallest epithelium lined the trachea; the shortest, the respiratory bronchiole. The most cells per unit length of basement membrane were in proximal intrapulmonary bronchi; the least, in the respiratory bronchiole. The nonciliated bronchiolar epithelial or Clara cell was restricted to respiratory bronchioles. Sulfomucins were present in the vast majority of surface goblet cells in the trachea and proximal bronchi. In proximal bronchi, neutral glycoconjugates predominated in glands and acidic glycoconjugates in surface epithelium. In terminal and respiratory bronchioles the ratio of acidic glycoconjugate to neutral glycoconjugate equaled that in proximal bronchi, although glands were not present. Sulfomucins were minimal in terminal airways. We conclude that the characteristics of the epithelial lining of the mammalian tracheobronchial airway tree are very species-specific. The lining of the rhesus monkey does not have the diversity in cell types in different airway generations observed in sheep and rabbit. Also, the populations lining these airways in the rhesus are very different from either the sheep or rabbit in number, proportions of different cell types, glycoconjugate content, and distribution of specific cell types.

Morphology and morphometry of the normal lung of the adult vervet monkey (Cercopithecus aethiops)

The lungs of four adult specimens of the vervet monkey (Cercopithecus aethiops) have been examined by transmission and scanning electron microscopy. A morphometric evaluation of the structural components directly involved in gas exchange has been carried out and the data have been modelled to estimate the anatomical diffusing capacity of the lung. The upper air-conducting airways of the lung were lined by an epithelium characterized by ciliated cells among which were dispersed goblet cells. The alveolar surface was lined by squamous type I pneumocytes and cuboidal type II granular pneumocytes. The blood-gas (tissue) barrier consisted of an epithelial cell, a common basal lamina, and an endothelial cell in the thin parts of the interalveolar septum. In the thicker parts of the septum, an interstitial space interposed between the basal laminae of the epithelial and endothelial cells contained supportive elements such as collagen, elastic tissue, and fibrocytes. The alveoli, the blood capillaries, and septal tissue composed 73%, 16%, and 11%, respectively, of the parenchyma. The harmonic and arithmetic mean thicknesses of the blood-gas (tissue) barrier were 0.311 micron and 1.048 microns; the surface area of the blood-gas (tissue) barrier per unit body weight was 50 cm2g-1, and the surface density was 117 mm2.mm3-1. The weight-specific total morphometric diffusing capacity was 0.11 mlO2 (sec.mbar.kg)-1. In comparison, the pulmonary morphometric characteristics of vervet monkey lung were superior to those of the other primates (Macaca irus, M. mulatta, and Homo sapiens) for which equivalent data are available. The gas-exchange potential of the lungs of the nonhuman primates as revealed by morphometric studies surpasses that of man, a feature that can be attributed to the relatively less energetic human lifestyle.

Tracheobronchial epithelium of the sheep: III. Carbohydrate histochemical and cytochemical characterization of secretory epithelial cells

We examined histochemically (light microscopy-LM) and cytochemically (electron microscopy-EM) the secretory epithelial cells in the tracheobronchial mucosa of sheep. Six morphologically distinct, granule-containing cells have been described, on the basis of their morphology and airway distribution: four mucous (M1-M4), serous (SC), and Clara (CC). Stereological and morphometric data indicated that M3, M4, SC, and CC were distinctly different from each other and from M1 and M2 cells. Mucous cells M1 and M2 differed in granule morphology. Samples of tracheas, sixth-generation bronchi, distal bronchi, and terminal bronchioles of 18 adult sheep were examined. At the LM level, methacrylate sections were reacted with an alcian blue (pH 2.5), periodic acid Schiff (PAS) sequence to differentiate neutral from acidic glycoconjugates (GC), and a high-iron diamine (HID), alcian blue sequence to differentiate sulfated from nonsulfated (sialylated) GC. At the EM level the periodic acid-thiocarbohydrazide localized hexose-rich, neutral GC. Dialyzed iron (DI) and high-iron diamine localized carboxylated and sulfated GC, respectively. Granules of all but Clara cells were PAS-positive. All mucous cells contained acidic groups, but only M1 and M4 cells had LM-detectable sulfated GC. At the ultrastructural level, minimal but discernible HID and LID reaction product was observed on granule profiles of M2, M3, and SC, indicating acidic and sulfated GC not detected at the LM level. Histochemically, the sheep tracheobronchial epithelium was more similar to that of humans than some other examined mammalian species.

Nonolfactory surface epithelium of the nasal cavity of the bonnet monkey: a morphologic and morphometric study of the transitional and respiratory epithelium

The purpose of the present study was to characterize ultrastructurally the nonolfactory nasal epithelium of a nonhuman primate, the bonnet monkey. Nasal cavities from eight subadult bonnet monkeys were processed for light microscopy, and scanning and transmission electron microscopy. Nonolfactory epithelium covered the majority of the nasal cavity and consisted of squamous (SE), transitional (TE), and respiratory epithelium (RE). Stratified SE covered septal and lateral walls of the nasal vestibule, while ciliated pseudostratified RE covered most of the remaining nasal cavity. Stratified, nonciliated TE was present between SE and RE in the anterior nasal cavity. This epithelium was distinct from the other epithelial populations in abundance and types of cells present. TE was composed of lumenal nonciliated cuboidal cells, goblet cells, small mucous granule (SMG) cells, and basal cells, while RE contained ciliated cells, goblet cells, SMG cells, basal cells, and cells with intracytoplasmic lumina lined by cilia and microvilli. TE and RE contained similar numbers of total epithelial cells and basal cells per millimeter of basal lamina. TE was composed of more SMG cells but fewer goblet cells compared to RE. We conclude that nonolfactory nasal epithelium in the bonnet monkey is complex with distinct regional epithelial populations which must be recognized before pathologic changes within this tissue can be assessed adequately.

Carbohydrate cytochemistry of rhesus monkey tracheal submucosal glands

This study was designed to characterize the ultrastructure and carbohydrate content of secretory cells in submucosal glands of rhesus monkey and to compare this information with that available for humans. The tracheas from five adult monkeys were fixed by airway infusion, processed, and embedded for both light and transmission electron microscopy. Histochemical strains including alcian blue-periodic acid-Schiff, dialyzed iron, and high-iron diamine-alcian blue were applied to serial glycol methacrylate sections. The cytochemical stains used included periodic acid-thiocarbohydrazide-silver proteinate, high-iron diamine, and low-iron diamine. The glandular secretory cells were divided into four categories based on ultrastructure and location within the gland. Cells in the first category resembled the mucous cell of the surface epithelium and were located in ducts most proximal to the tracheal lumen. The second category consisted of cells that were located in distal ducts and contained large electron-lucent granules. The granules in both of these cell groups contained material that was periodate-reactive and sulfated. Cells of the third category contained granules that were either electron-lucent or electron-dense. These cells, which were difficult to characterize as either serous or mucous, were located in secretory tubules and acini and contained periodate-reactive glycoconjugates that were either sulfated or nonsulfated. The last category consisted mainly of cells that contained electron-dense granules that were lightly periodate-reactive or a few that were unreactive with any of the cytochemical methods used here.(ABSTRACT TRUNCATED AT 250 WORDS)

Differentiation of tracheal epithelium during fetal lung maturation in the rhesus monkey Macaca mulatta

Of the eight categories of epithelial cells identified in pulmonary conducting airways, four are found in the trachea of adult primates: basal, mucous goblet, intermediate, and ciliated cells. While their ultrastructure is well characterized, little is understood about their origin or differentiation. This study describes the pattern of differentiation of the tracheal luminal epithelium in a species of nonhuman primate, the rhesus monkey, Macaca mulatta. Tracheas of 57 fetal and postnatal rhesus were fixed with glutaraldehyde/paraformaldehyde: ten at 29-54 days gestational age (GA), ten at 59-80 days GA (pseudoglandular stage), sixteen at 82-130 days GA (canalicular stage), ten at 141-168 days GA (saccular stage), eight at 1-134 days postnatal, and three adults (2 yr 11 months to 11 yr 11 months). Slices taken proximal to the carina were processed for electron microscopy by a selective embedding procedure. In the youngest fetuses, essentially one population of cells lined the tracheal epithelial surface. These cells were columnar in shape with a central nucleus, few organelles, and large amounts of cytoplasmic glycogen. At 46 days GA, ciliated cells were observed on the membranous side of the trachea. Some nonciliated cells had concentrations of organelles in the most apical portion of their cytoplasm. At 59 days GA, membrane-bound cored granules were intermixed with organelles in the apices of some glycogen-filled cells. They were observed first on the cartilaginous side. Between 59 and 100 days GA, a large number of cell forms which appeared to be transitional between ciliated, secretory, basal, and undifferentiated cells were present. These included ciliated cells with electron-lucent inclusions resembling mucous granules. Mucous secretory cells were more numerous and had more granules and less glycogen in older fetuses. By 105 days GA, few of the secretory cells had significant amounts of glycogen and the cytoplasm was condensed. Secretory granules were very abundant in some cells and minimal in others. The Golgi apparatus was prominent. In animals 120 days GA and older, small mucous granule cells and basal cells resembling these cells in adults were present. By 134 days postnatal age, the epithelium resembled that in adults. We conclude that most of the differentiation of tracheal epithelium in the rhesus monkey occurs prior to birth; the cells differentiate in the following sequences: ciliated, mucous goblet, small mucous granule, basal; and basal and small mucous granule cells do not play a role in ciliated and mucous cell formation in the fetus.