A qualitative and quantitative study of the lung of an ostrich,Struthio camelus

The ostrich lung, with its lack of interparabronchial septa, the presence of very shallow atria and exceptional morphometric refinement, structurally resembles those of small, energetic flying birds, whereas it also displays features characteristic of the flightless ratites in which the neopulmo is relatively poorly developed and a segmentum accelerans may be generally lacking. The large size of the bronchial system of the ostrich may help explain the unique shifts in the airflow pathways that must occur from resting to panting breathing, explaining its insensitivity to acid–base imbalance of the blood during sustained panting under thermal stress. The mass-specific volume of the lung is 39.1 cm3kg−1 and the volume density of the exchange tissue is remarkably high (78.31%). The blood–gas (tissue) barrier is relatively thick (0.56μm) but the plasma layer is very thin (0.14μm). In this flightless ratite bird, the mass-specific surface area of the tissue barrier (30.1 cm2g−1), the mass-specific anatomical diffusing capacity of the tissue barrier for oxygen (0.0022mlO2s−1Pa−1kg−1), the mass-specific volume of pulmonary capillary blood (6.25 cm3kg−1) and the mass-specific total anatomical diffusing capacity for oxygen (0.00073mlO2s−1Pa−1kg−1) are equivalent to or exceed those of much smaller highly aerobic volant birds. The distinctive morphological and morphometric features that seem to occur in the ostrich lung may explain how it achieves and maintains high aerobic capacities and endures long thermal panting without experiencing respiratory alkalosis.

What it takes to fly: the structural and functional respiratory refinements in birds and bats

In absolute terms, flight is a highly energetically expensive form of locomotion. However, with respect to its cost per unit distance covered, powered flight is a very efficient mode of transport. Birds and bats are the only extant vertebrate taxa that have achieved flight. Phylogenetically different, they independently accomplished this elite mode of locomotion by employing diverse adaptive schemes and strategies. Integration of functional and structural parameters, a transaction that resulted in certain trade-offs and compromises, was used to overcome exacting constraints. Unique morphological, physiological and biochemical properties were initiated and refined to enhance the uptake, transfer and utilization of oxygen for high aerobic capacities. In bats, exquisite pulmonary structural parameters were combined with optimal haematological ones: a thin blood-gas barrier, a large pulmonary capillary blood volume and a remarkably extensive alveolar surface area in certain species developed in a remarkably large lung. These factors were augmented by, for example, exceptionally high venous haematocrits and haemoglobin concentrations. In birds, a particularly large respiratory surface area and a remarkably thin blood-gas (tissue) barrier developed in a small, rigid lung; a highly efficient cross-current system was fabricated within the parabronchi. The development of flight in only four animal taxa (among all the animal groups that have ever evolved; i.e. insects, the now-extinct pterosaurs, birds and bats) provides evidence for the enormous biophysical and energetic constraints that have stymied volancy. Bats improved a fundamentally mammalian lung to procure the large amounts of oxygen needed for flight. The lung/air sac system of birds is not therefore a prescriptive morphology for flight: the essence of its design can be found in the evolution of the reptilian lung, the immediate progenitor stock from which birds arose. The attainment of flight is a classic paradigm of the remarkable adaptability inherent in organismal and organic biology for countering selective pressures by initiating elegant morphologies and physiologies.

Inspiratory aerodynamic valving in the avian lung: functional morphology of the extrapulmonary primary bronchus

The form, geometry and epithelial morphology of the extrapulmonary primary bronchi (EPPB) of the domestic fowl (Gallus gallus var. domesticus) and the rock dove (Columba livia) were studied microscopically and by three-dimensional computer reconstruction to determine the structural features that may be involved in the rectification of the inspired air past the openings of the medioventral secondary bronchi (MVSB), i.e. the inspiratory aerodynamic valving (IAV). In both species, the EPPB were intercalated between the clavicular and the cranial thoracic air-sacs. A notable difference between the morphology of the EPPB in G. g. domesticus and C. livia was that, in the former, the EPPB were constricted at the origin of the MVSB, while a dilatation occurred at the same site in the latter. In both species, a highly vascularized, dorsally located hemispherical epithelial swelling was observed cranial to the origin of the MVSB. The MVSB were narrow at their origin and variably angled relative to the longitudinal axis of the EPPB. Conspicuous epithelial tracts and folds were observed on the luminal aspect of the EPPB in both C. livia and G. g. domesticus. From their marked development and their orientation relative to the angled MVSB, these properties may influence the flow of the air in the EPPB. It was concluded that features such as syringeal constriction, an intimate topographic relationship between the EPPB and the cranial air-sacs, prominent epithelial tracts and folds, an epithelial swelling ahead of the origin of the first MVSB (corresponding to the ‘segmentun accelerans’), and narrowing and angulation of the MVSB at their origin, may together contribute to IAV to a variable extent. In as much as the mechanism of pulmonary ventilation and mode of airflow in the parabronchial lung are basically similar in all birds, the morphological differences observed between G. g. domesticus and C. livia suggest that either the mechanism of production of IAV or its functional efficiency may be different, at least in these two species of birds.

Is the sheet-flow design a 'frozen core' (a Bauplan) of the gas exchangers? Comparative functional morphology of the respiratory microvascular systems: illustration of the geometry and rationalization of the fractal properties

The sheet-flow design is ubiquitous in the respiratory microvascular systems of the modern gas exchangers. The blood percolates through a maze of narrow microvascular channels spreading out into a thin film, a "sheet". The design has been convergently conceived through remarkably different evolutionary strategies. Endothelial cells, e.g. connect parallel epithelial cells in the fish gills and reptilian lungs; epithelial cells divide the gill filaments in the crustacean gills, the amphibian lungs, and vascular channels on the lung of pneumonate gastropods; connective tissue elements weave between the blood capillaries of the mammalian lungs; and in birds, the blood capillaries attach directly and in some areas connect by short extensions of the epithelial cells. In the gills, skin, and most lungs, the blood in the capillary meshwork geometrically lies parallel to the respiratory surface. In the avian lung, where the blood capillaries anastomose intensely and interdigitate closely with the air capillaries, the blood occasions a 'volume' rather than a 'sheet.' The sheet-flow design and the intrinsic fractal properties of the respiratory microvascular systems have produced a highly tractable low-pressure low-resistance region that facilitates optimal perfusion. In complex animals, the sheet-flow design is a prescriptive evolutionary construction for efficient gas exchange by diffusion. The design facilitates the internal and external respiratory media to be exposed to each other over an extensive surface area across a thin tissue barrier. This comprehensive design is a classic paradigm of evolutionary convergence motivated by common enterprise to develop corresponding functionally efficient structures. With appropriate corrections for any relevant intertaxa differences, use of similar morphofunctional models in determining the diffusing capacities of various gas exchangers is warranted.

Functional morphology of the gas-gland cells of the air-bladder of Oreochromis alcalicus grahami (teleostei: cichlidae): an ultrastructural study on a fish adapted to a severe, highly alkaline environment

Oreochromis alcalicus grahami is a small cichlid fish that lives in shallow peripheral lagoons of Lake Magadi, Kenya. The internal surface of the air-bladder is highly vascularized, illustrating possible utilization as an accessory respiratory organ. The wall of the bladder consists of five distinct tissue layers. From the outer to the inner surfaces are: a squamous, undifferentiated epithelial cell; a collagen-elastic tissue space; a smooth muscle tissue band; an inner connective tissue space; and columnar gas-gland cells projecting into the lumen. The cell membrane over the perikarya of the gas-gland cells was sporadically broken. The disruptions were ascribed to possible physical damage by discharging gas-bubbles. Juxtaluminally, the gas-gland cells attached across tight junctions. The cells have highly euchromatic nuclei and conspicuously large intracytoplasmic secretory bodies. On the blood capillary facing (basal) aspect, the cell membrane of the gas-gland cells is highly amplified. The cells insert onto a smooth muscle tissue band. The morphological features and the topographical arrangement of the gas-gland cells in O. a. grahami are indicative of an operative exchange of materials between them and the underlying tissue components especially the blood capillaries. For a fish that subsists in hot, highly saline and alkaline water heavily invested by avian predators and where the partial pressure of oxygen diurnally shifts from virtual anoxia to hyperoxia, development of a versatile air-bladder for efficient buoyancy control conforms to the functional demands placed on it by a unique environment. Illustratively, instead of the gas-gland morphology in O. a. grahami resembling that in the freshwater fishes, the group from which the fish has evolved, it compares more closely to that of the marine fish. This similarity suggests amazing parallel evolutionary adaptation to biophysically corresponding aquatic milieus.

Comparative respiratory morphology: themes and principles in the design and construction of the gas exchangers

Along the evolutionary continuum, a kaleidoscope of gas exchangers has evolved from the simple cell membrane of the primeval unicells. The most momentous events in this process were: the intensification of molecular oxygen in the biosphere and its appropriation into aerobic metabolism, the rise of multicellular organisms, the development of a circulatory system and carrier pigments in blood, the advocacy of air breathing, adoption of suctional breathing, and the shift to endothermy. To satisfy species-specific needs for oxygen, some constraints were overcome through transactions that obliged certain compromises and trade-offs. Optimal designs of the gas exchangers for particular phylogenetic levels of development, habitat, and lifestyle have developed only so far as to satisfy prescribed needs. The efficiency of the human lung, for example, falls well below those of certain taxa that are considered to be relatively "less advanced." Utilizing different resources and strategies, in fascinating processes of conformity, different groups of animals have developed similar respiratory structures. In most cases, the analogy reflects evolutionary convergence in response to corresponding selective pressures rather than common ancestry. Anat Rec (New Anat) 261:25-44, 2000.

Surface specialization of the capillary endothelium in the pecten oculi of the chicken, and their overt roles in pectineal haemodynamics and nutrient transfer to the inner neural retina

The structure of the capillary endothelium in the pecten oculi of the domestic fowl was investigated by scanning and transmission electron microscopy. Scanning electron microscopy results demonstrated the existence of a vast array of irregular microplicae that projected from the luminal surface of the capillary endothelium. In between these microplicae were numerous crevices. The microplicae were closely packed and showed no preferred orientation regarding either the longitudinal or transverse plane of the capillaries. Transmission electron microscopy revealed the section profiles of the microplicae: their tortuity, branching, interdigitations and the magnitude of the crevices contained. The endothelial cytoplasm exhibited a few mitochondria and micropinocytotic vesicles. The apparent set-up of the luminal plasmalemmal infoldings seemed to be designed for effecting impedance to the pectineal blood flow and thereby facilitating passive permeation of blood-borne nutrients to the inner neural retina. The reasons of such passive transport operation mediated by the endothelial microplicae of the avian pecten oculi are discussed in the perspective of the existing literature.

Adaptations of a tropical swamp worm, alma emini, for subsistence in a H2S-rich habitat: evolution of endosymbiotic bacteria, sulfide metabolizing bodies, and novel processes of elimination of neutralized sulfide complexes

The epithelial cell lining of the respiratory groove of Alma emini, an oligochaete glossoscolecid worm that lives in a hydrogen sulfide (H2S)-rich tropical swamp, was investigated by transmission electron microscopy to determine the underlying structural adaptations which enable the worm to subsist in a highly inimical habitat. The epithelium of the respiratory groove is made up of squamous cells with a highly amplified free epithelial surface. The cells are tightly packed with electron dense sulfur metabolizing bodies (SMBs) and contain endosymbiotic bacteria. Presence of sulfur in the electron dense SMBs was confirmed by X-ray microanalysis. Certain eukaryotic cells with prominent filopodia-like cytoplasmic extensions were observed under the epithelial cells and in the muscle tissue. The cells contained numerous heteromorphic endosymbiotic bacteria and scattered SMBs. Both the SMBs and the bacteria are reckoned to be involved in scavenging and detoxifying H2S. The removal of sulfide complexes was observed to occur through excision of blebs formed by epithelial cell membrane elaborations and by exocytosis of crystalline-like particles. These adaptive stratagems generally correspond with those that have been adopted by many marine and hydrothermal vent organisms that occupy sulfide-rich biomes. The congruent adaptive stratagems and ultrastructural morphologies in such a diverse community of organisms have been imposed by a common need to neutralize the insidious effects of H2S in their environments. Copyright 1998 Academic Press.

A scanning electron microscope study of the luminal surface specializations in the blood vessels of the pecten oculi in a diurnal bird, the black kite (Milvus migrans)

The luminal surface of the pecten oculi of the black kite (Milvus migrans), a diurnally active bird of prey, was examined by scanning electron microscopy. In this species the blood vessels are generally of two types, the small-calibre capillaries and the large-calibre afferent and efferent vessels. The luminal surface of the efferent blood vessels possesses a few low microplicae. Conversely, the luminal surface of the afferent blood vessels is characteristically smooth except at the cell junctions and at the point of entry into the capillaries. The cells junctions are marked by low ragged ridges while the luminal surface is studded with low sparse pleiomorphic microprojections at the point of capillary emergence. The luminal surface of the blood capillaries is characterised by a labyrinth of closely disposed microplicae that projects into the lumen. These microplicae show no particular orientation with respect to either the longitudinal or transverse axis of the capillary. Instead, they are diffusely orientated. It is conjectured that such a heterogeneous design of the endothelium in the blood vessels of the pecten oculi has developed in order to augment the role of the pecten in the transport of nutrients to the avascular neural retina by an energy saving diffusion process. The process through which the design of the microfolds affects haemodynamics and their putatite role in facilitating the delivery of nutrients are discussed in the perspective of the available data.

Structure and function of the axillary organ of the gulf toadfish, Opsanus beta (Goode and Bean)

The structure of the axillary organ of a batrachoidid species, the gulf toadfish (Opsanus beta Goode and Bean 1879), has been examined and several simple experiments designed to elucidate its function performed. Electron microscopy (EM) studies revealed cells and structures suggesting secretory and iono regulatory roles (e.g., abundant intracytoplasmic secretory particles, rough endoplasmic reticulum, sparse Golgi bodies, indented epithelial cells with microvilli, numerous endocytotic vesicles, etc.). Our physiological experiments allowed us to reach several conclusions: the organs do not excrete significant quantities of urea relative to other areas of the fish (head and gills), the organs do not secrete a substance that is toxic to a teleost test fish (Gambusia affinis), the secretions do not induce short-term modifications in locomotory activity of other gulf toadfish (e.g., by pheromonal means) and the secretions do not inhibit the growth of several species of microorganisms in culture. The function of the organ and its secretions remains unknown, representing a fertile area for research on structure and function in comparative physiology.

A stereological comparison of villous and microvillous surfaces in small intestines of frugivorous and entomophagous bats: species, inter-individual and craniocaudal differences

The extents of functional surfaces (villi, microvilli) have been estimated at different longitudinal sites, and in the entire small intestine, for three species of bats belonging to two feeding groups: insect- and fruit-eaters. In all species, surface areas and other structural quantities tended to be greatest at more cranial sites and to decline caudally. The entomophagous bat (Miniopterus inflatus) had a mean body mass (coefficient of variation) of 8.9 g (5%) and a mean intestinal length of 20 cm (6%). The surface area of the basic intestinal tube (primary mucosa) was 9.1 cm2 (10%) but this was amplified to 48 cm2 (13%) by villi and to 0.13 m2 (20%) by microvilli. The total number of microvilli per intestine was 4 x 10(11) (20%). The average microvillus had a diameter of 8 nm (10%), a length of 1.1 microns (22%) and a membrane surface area of 0.32 micron 2 (31%). In two species of fruit bats (Epomophorus wahlbergi and Lisonycteris angolensis), body masses were greater and intestines longer, the values being 76.0 g (18%) and 76.9 g (4%), and 73 cm (16%) and 72 cm (7%), respectively. Surface areas were also greater, amounting to 76 cm2 (26%) and 45 cm2 (8%) for the primary mucosa, 547 cm2 (29%) and 314 cm2 (16%) for villi and 2.7 m2 (23%) and 1.5 m2 (18%) for microvilli. An increase in the number of microvilli, 33 x 10(11) (19%) and 15 x 10(11) (24%) per intestine, contributed to the more extensive surface area but there were concomitant changes in the dimensions of microvilli. Mean diameters were 94 nm (8%) and 111 nm (4%), and mean lengths were 2.8 microns (12%) and 2.9 microns (10%), respectively. Thus, an increase in the surface area of the average microvillus to 0.83 micron 2 (12%) and 1.02 microns 2 (11%) also contributed to the greater total surface area of microvilli. The lifestyle-related differences in total microvillous surface areas persisted when structural quantities were normalised for the differences in body masses. The values for total microvillous surface area were 148 cm2g-1 (20%) in the entomophagous bat, 355 cm2g-1 (20%) in E. wahlbergi and 192 cm2g-1 (17%) in L. angolensis. This was true despite the fact that the insecteater possessed a greater length of intestine per unit of body mass: 22 mm g-1 (8%) versus 9-10 mm g-1 (9-10%) for the fruit-eaters.

Stereological methods for estimating the functional surfaces of the chiropteran small intestine

A tissue sampling protocol has been devised for studying the functional surfaces of chiropteran small intestine and drawing comparisons within and between species. The goal was to obtain minimally biased stereological estimates of villous and microvillous surface areas and the numbers of microvilli. The approach is illustrated using the intestines of 3 bats (from frugivorous and entomophagous groups) and is based on the use of vertical sections and cycloid test arcs. A sampling scheme with 3 levels was employed. At level 1 (macroscopy), primary mucosal area was estimated from intestinal length and perimeter. Amplification factors due to villi were estimated at level 2 (light microscopy, LM) whilst microvillous amplifications were estimated at level 3 (transmission electron microscopy, TEM). The absolute surfaces, lengths and diameters of microvilli were used to calculate packing densities and absolute numbers. Estimated villous surface areas of the entire small intestine were 44.4 cm2 (Miniopterus inflatus, entomophagous), 410 cm2 (Epomophorus wahlbergi, frugivorous) and 237 cm2 (Lisonycteris angolensis, frugivorous). Corresponding microvillous surface areas were 0.11, 1.69 and 1.01 m2 whilst the numbers of microvilli per intestine were 4.5, 23.4 and 8.8 x 10(11). When normalised for body weights, microvillous surfaces were 122, 246 and 133 cm2/g respectively. The functional surfaces of the fruit bat appear to be more extensive than those of the entomophagous bat.

A scanning electron microscope study of the pecten oculi of the black kite (Milvus migrans): possible involvement of melanosomes in protecting the pecten against damage by ultraviolet light

The pecten oculi of the black kite (Milvus migrans), a diurnally active bird of prey, has been examined by scanning electron microscopy. In this species the pecten consists of 12 highly vascularised pleats, held together apically by a heavily pigmented 'bridge' and projects freely into the vitreous body in the ventral part of the eye cup. Ascending and descending blood vessels of varying calibre, together with a profuse network of capillaries, essentially constitute the vascular framework of the pecten. A distinct distribution of melanosomes is discernible on the pecten, the concentration being highest at its apical end, moderate at the crest of the pleats and least at the basal and lateral margins. Overlying and within the vascular network, a close association between blood vessels and melanocytes is evident. It is conjectured that such an association may have evolved to augment the structural reinforcement of this nutritive organ in order to keep it firmly erectile within the gel-like vitreous. Such erectility may be an essential prerequisite for its optimal functioning, as well as in its overt use as a protective shield against the effects of ultraviolet light, which otherwise might lead to damage of the pectineal vessels.

A clinical trial of buparvaquone in the treatment of East Coast fever

A clinical trial was conducted to test buparvaquone (Butalex; Coopers Pitman-Moore) in the treatment of East Coast fever under field conditions in Kenya. Data from 229 cases were analysed following treatment with one (69), two (142) or three (18) doses at 2.5 mg/kg. The majority of cattle (95.2 per cent) were exotic (Bos taurus) or improved (Bos taurus cross Bos indicus) and 39.3 per cent were infected with Anaplasma marginale. There was an overall recovery rate of 85.6 per cent, with 90.1 per cent recovering following one treatment and 75.4 per cent recovering following two treatments. At a follow-up visit three to six months after completion of the trial data was obtained on 224 cases. Thirty had died, 13 of which were reported to have been from East Coast fever, nine had been sold and six slaughtered. Of the remaining 146, 86.3 per cent were in good condition, 13.7 per cent fair and 2.0 per cent in poor condition. A two dose regimen was most effective and should be recommended except in very early cases or those under direct veterinary supervision.

A morphometric study of the lungs of different sized bats: correlations between structure and function of the chiropteran lung

1. The lungs of four species of bats, Phyllostomus hastatus (PH, mean body mass, 98 g), Pteropus lylei (PL, 456 g), Pteropus alecto (PA, 667 g), and Pteropus poliocephalus (PP, 928 g) were analysed by morphometric methods. These data increase fivefold the range of body masses for which bat lung data are available, and allow more representative allometric equations to be formulated for bats. 2. Lung volume ranged from 4.9 cm3 for PH to 39 cm3 for PP. The volume density of the lung parenchyma (i.e. the volume proportion of the parenchyma in the lung) ranged from 94% in PP to 89% in PH. Of the components of the parenchyma, the alveoli composed 89% and the blood capillaries about 5%. 3. The surface area of the alveoli exceeded that of the blood-gas (tissue) barrier and that of the capillary endothelium whereas the surface area of the red blood cells as well as that of the capillary endothelium was greater than that of the tissue barrier. PH had the thinnest tissue barrier (0.1204 microns) and PP had the thickest (0.3033 microns). 4. The body mass specific volume of the lung, that of the volume of pulmonary capillary blood, the surface area of the blood-gas (tissue) barrier, the diffusing capacity of the tissue barrier, and the total morphometric pulmonary diffusing capacity in PH all substantially exceeded the corresponding values of the pteropid species (i.e. PL, PA and PP). This conforms with the smaller body mass and hence higher unit mass oxygen consumption of PH, a feature reflected in the functionally superior gas exchange performance of its lungs. 5. Morphometrically, the lungs of different species of bats exhibit remarkable differences which cannot always be correlated with body mass, mode of flight and phylogeny. Conclusive explanations of these pulmonary structural disparities in different species of bats must await additional physiological and flight biomechanical studies. 6. While the slope, the scaling factor (b), of the allometric equation fitted to bat lung volume data (b = 0.82) exceeds the value for flight VO2max (b = 0.70), those for the surface area of the blood-gas (tissue) barrier (b = 0.74), the pulmonary capillary blood volume (b = 0.74), and the total morphometric lung diffusing capacity for oxygen (b = 0.69) all correspond closely to the VO2max value. 7. Allometric comparisons of the morphometric pulmonary parameters of bats, birds and non-flying mammals reveal that superiority of the bat lung over that of the non-flying mammal.(ABSTRACT TRUNCATED AT 400 WORDS)

A morphometric analysis of chloride cells in the gills of the teleosts Oreochromis alcalicus and Oreochromis niloticus and a description of presumptive urea-excreting cells in O. alcalicus

The gills of Oreochromis alcalicus, a hyperosmotic and low pH adapted teleost, and Oreochromis niloticus, a freshwater closely related fish have been investigated by transmission electron microscopy and a morphometric analysis of, particularly, the chloride cells and their primary organelles, the mitochondria and the tubulo-vesicular system carried out. Oreochromis alcalicus had a fourfold greater number of chloride cells than O. niloticus and the chloride cells had more mitochondria and a more profuse tubulo-vesicular matrix. The ultrastructural features of the chloride cells of Oreochromis alcalicus were interpreted as adaptations for the severe ecosystem that the species inhabits. Putative urea excreting cells unique to the gills of Oreochromis alcalicus are described.

A morphological and morphometric study of the prosimian lung: the lesser bushbaby Galago senegalensis

The lung of the lesser bushbaby (Galago senegalensis) has been investigated morphologically and morphometrically using the transmission and scanning electron microscopes. Grossly and microscopically, the bushbaby lung was found to be essentially similar to that of the other primates and the mammals in general. Subtle morphometric differences were, however, observed, with the bushbaby lung being generally structurally less sophisticated than that of the other primates on which comparable data are available, except for man. The weight-specific surface area of the blood-gas (tissue) barrier in G. senegalensis was 25 cm2 g-1. The thickness of the blood-gas barrier was 0.355 micron and the weight specific total anatomical pulmonary diffusing capacity 0.045 mlO2 sec-1 mbar1 kg-1. The morphological similarity of the galago lung to that of man gives sufficient grounds to justify its possible use in human pulmonary studies but caution has been called for in the general utilisation of primate tissues without first establishing their morphological characteristics, just because the primates are taken to be evolutionally close to man. The dearth of morphological studies on the various organ systems of the prosimians is pointed out.

A study of the morphology of the gills of an extreme alkalinity and hyperosmotic adapted teleost Oreochromis alcalicus grahami (Boulenger) with particular emphasis on the ultrastructure of the chloride cells and their modifications with water dilution. A SEM and TEM study

The general gill morphology of Oreochromis alcalicus grahami, a teleost adapted to high salinity and hyperosmosis, is basically similar to that of other teleostean fish. The species has four pairs of gill arches, all of which have well developed filaments. Each of the arches (holobranchs) has two rows of filaments (hemibranchs). Bilaterally situated secondary lamellae branch from the central axis of the filaments. The lamellae reach their maximum size at the middle of the filament, gradually decrease in size and eventually disappear towards the tip of the filament, which is bare. The leading edge of the gill filament and the immediate interlamellar space is covered by a stratified epithelium consisting of pavement cells, mucous cells, chloride cells and undifferentiated cells. The surface of these cells is made up of concentric microridges. The chloride cells were found only on the primary epithelium (filamental epithelium) and very rarely on the secondary epithelium (lamellar epithelium). Two types of chloride cells were observed in the gills of Oreochromis. The superficial chloride cells have fewer mitochondria concentrated towards the basal aspect of the cell, and a network of tubules towards the apical surface and are less electron dense. These cells intercommunicate with the water through an apical pore. The deep chloride cells have numerous diffuse mitochondria intercalated between a fine profuse tubular network and are more electron dense. These cells are covered by one or more layers of pavement cells and thus do not have access to the external surface. After gradual dilution of the lake water in which the fish were kept, both types of chloride cells remained topographically and ultrastructurally distinct. However, in both kinds of cell the mitochondria decreased in number and size. Initially there was an increase in the diameter and the degree of interdigitation of the tubules followed by a gradual decrease. An increase in the quantity of rough endoplasmic reticulum, particularly at the perinuclear region of the cell, was noted. The morphometric analysis of the branchial system indicated that the gills of Oreochromis are well adapted for gas exchange by having numerous and relatively long gill filaments with a high lamellar density. These features provide a large surface for gas exchange which, when coupled with the notably thin water-blood barrier of an average thickness of only 0.83 micro, would facilitate efficient absorption of oxygen by the gills. Oreochromis alcalicus was observed to be incapable of adapting to freshwater. This may have been due to the progressive degeneration of the chloride cells.(ABSTRACT TRUNCATED AT 400 WORDS)

The morphology of the lung of the black mamba Dendroaspis polylepis (Reptilia: Ophidia: Elapidae). A scanning and transmission electron microscopic study

The lung of a snake, the black mamba (Dendroaspis polylepis), has been investigated by scanning and transmission electron microscopy. This species has only one lung, the right, which is long and occupies most of the pleuro-peritoneal cavity. Grossly, the lung could be divided into two discrete anatomical regions: an anterior respiratory area made up of a honeycomb network of capillary-bearing partitions, and a posterior membranous saccular region. The exchange region consisted of a central air duct, the bronchus, which was delineated both dorsally and laterally by morphologically and spatially distinct hierarchically arranged septa. The primary septa gave rise to the secondary septa from which the much deeper peripherally situated tertiary septa that formed the immediate openings to the faveoli arose. The faveoli were rather parallel elongated pockets separated by partitions, the interfaveolar septa, and terminated peripherally on the pleura. A double capillary disposition of the blood capillaries was observed on the relatively thick primary and secondary septa. These septa were lined by a heterogenous epithelium made up of ciliated cells, secretory cells, and smooth squamous cells. This epithelium was continued from the trachea and the bronchus. At the faveolar level the blood capillaries exhibited a single system where they formed a matrix on both sides of the partitions. The surface of the faveoli was covered by two types of cells: Type I cells were squamous and their remarkably attenuated cytoplasmic arborisations were notably extensive while the Type II cells were rather cuboidal, bore stubby microvilli and contained the characteristic osmiophilic lamellated bodies. On the basis of the clearly evident complete differentiation of the pneumocytes and the presence of both the double and single capillary systems, it was observed that this lung, and apparently the reptilian lung in general, manifests a transitional developmental and structural stage in the evolution of the lungs of the air-breathing vertebrates from lower through to higher vertebrates. The gross and ultrastructural heterogeneity of the organisation of the ophidian lung is illustrated and the dearth of pulmonary morphological data in this taxon is pointed out.

An allometric study of pulmonary morphometric parameters in birds, with mammalian comparisons

Comprehensive pulmonary morphometric data from 42 species of birds representing ten orders were compared with those of other vertebrates, especially mammals, relating the comparisons to the varying biological needs of these avian taxa. The total lung volume was strongly correlated with body mass. The volume density of the exchange tissue was lowest in the charadriiform and anseriform species and highest in the piciform, cuculiform and passeriform species. The surface area of the blood-gas (tissue) barrier, the volume of the pulmonary capillary blood and the total morphometric pulmonary diffusing capacity were all strongly correlated with body mass. The harmonic mean thickness of both the blood-gas (tissue) barrier and the plasma layer were weakly correlated with body mass. The mass-specific surface area of the blood-gas (tissue) barrier (surface area per gram body mass) and the surface density of the blood-gas (tissue) barrier (i.e. its surface area per unit volume of exchange tissue) were inversely correlated (though weakly) with body mass. The passeriform species exhibited outstanding pulmonary morphometric adaptations leading to a high specific total diffusing capacity per gram body mass, consistent with the comparatively small size and energetic mode of life which typify passeriform birds. The relatively inactive, ground-dwelling domestic fowl (Gallus gallus) had the lowest pulmonary diffusing capacity per gram body mass. The specific total lung volume is about 27% smaller in birds than in mammals but the specific surface area of the blood-gas (tissue) barrier is about 15% greater in birds. The ratio of the surface area of the tissue barrier to the volume of the exchange tissue was also much greater in the birds (170-305%). The harmonic mean thickness of the tissue barrier was 56-67% less in the birds, but that of the plasma layer was about 66% greater in the birds. The pulmonary capillary blood volume was also greater (22%) in the birds. Except for the thickness of the plasma layer, these morphometric parameters all favour the gas exchange capacity of birds. Consequently, the total specific mean morphometric pulmonary diffusing capacity for oxygen was estimated to be about 22% greater in birds than in mammals of similar body mass. This estimate was obtained by employing oxygen permeation constants for mammalian tissue, plasma and erythrocytes, as avian constants were not then available.(ABSTRACT TRUNCATED AT 400 WORDS)

Scanning electron microscope study of the morphology of the reptilian lung: the Savanna monitor lizard Varanus exanthematicus and the pancake tortoise Malacochersus tornieri

The morphology of the lungs of two reptilian species, Varanus exanthematicus and Malacochersus tornieri, have been studied on gross preparations, latex casts, and critical-point-dried tissues. The shape of these lungs was observed to conform with that of the body, the lung of the monitor lizard (Varanus) being long and ovoid while that of the pancake tortoise (Malacochersus) was rounded and laterally indented. With respect to the size distribution of the gas exchange compartments, the lungs were observed to be notably heterogenous. In both species these units were generally smaller in diameter in the cranial region of the lung while those in the caudal region were larger. The gas exchange compartments in the tortoise were more profusely compartmented with the primary, secondary, and tertiary septa being well developed while in the lizard only the primary and secondary septa were observed. The tertiary septa in the tortoise lung and the secondary septa in that of the monitor lizard defined the terminal gas exchange units, the faveoli. The cast impressions closely resembled the actual lung tissue and convincingly revealed the hierarchical design of the gas exchange compartments as they radiate from the air chambers and ducts, terminally giving rise to the faveoli. This stratification clearly increases the surface area available for gas exchange in these lungs. Disparate refinements of the basic reptilian lung design, as noted here, may lead to differing anatomic pulmonary diffusing capacities for oxygen to which characteristics like energetics and mode of respiration in this taxon may be attributed.

The morphology of the lung of the East African tree frog Chiromantis petersi with observations on the skin and the buccal cavity as secondary gas exchange organs: A TEM and SEM study

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Scanning and transmission electron microscopic study of the tracheal air sac system in a grasshopper Chrotogonus senegalensis (Kraus)--Orthoptera: Acrididae: Pyrgomorphinae

The morphology of the trachea-air sac system in a species of grasshopper Chrotogonus senegalensis has been studied by using scanning and transmission electron microscopes. Capacious air sacs were formed as dilatations along the primary tracheal trunks. Narrower secondary trachea arose either directly from the primary trachea that bypassed the air sacs or from the air sacs themselves. At or close to the organ or tissue supplied with air, the secondary trachea gave rise to the notably smaller tertiary trachea that penetrated the tissue, giving rise terminally to the extremely small tracheoles that indent some cells. The trachea and the air sacs were basically made up of an inner cuticular lining, helical taenidial rings, and an overlying epithelial cell cover. The air sacs may be important in efficient ventilation of the respiratory system. The supply of air directly to the tissue cells was viewed as an exemplary efficient design when compared to that prevailing in the nontracheate air-breathing animals, where the vascular system is interposed between the respiratory organ and the target tissue cells. A similarity in the general morphological design of the insect and avian respiratory systems has been observed, mainly in respect to the presence of the air sacs and that of the respiratory shunts. This, together with the reported functional features like the unidirectional mode of ventilation, has been interpreted as a classic case of structural and functional convergent evolution leading to the evolution of similar and comparably efficient respiratory systems capable of providing the large amount of oxygen demanded by flight.

The lung of the emu, Dromaius novaehollandiae: a microscopic and morphometric study

Qualitative and quantitative characteristics suggest that the lung of the emu is poorly adapted for gas exchange when compared with that of other birds. The granular epithelial cells extend over the air capillaries, and the squamous epithelial cells have microvilli indicating a poor differentiation of the epithelium of the exchange tissue. The surface area of the blood-gas tissue barrier per unit body mass was only 5.4 cm2/g, the volume of the pulmonary capillary blood per unit body mass was only 0.93 cm3/kg, and the tissue barrier was unusually thick (0.232 micron). These parameters produce a relatively small total morphometric pulmonary diffusing capacity for oxygen of 0.014 ml O2/sec/mbar/kg. The findings conform to the evolution of a very large flightless bird in a warm environment lacking effective predators.