Simple Squamous Epithelium Research Articles

Moderator Bands (Trabecula septomarginalis) of Mature Buffalo (Bos bubalis L.) with Special Emphasis on the Structure and Distribution of the Purkinje Cardiomyocytes: Histological and Histochemical

Ten hearts of mature healthy Buffalo (Bos bubalis L.) were employed to investigate the histological and histochemical structures of the moderator bands. Hearts were gently dissected and the moderator bands were collected. The specimens were processed histologically and subjected to different stains. Grossly, the moderator band (Septomarginal trabeculae) was a single muscular band that was found only in the right ventricle of the buffalo heart. It extended from the interventricular septum to the free ventricular wall especially at the base of the papillary muscle, crossing and passing through the ventricular cavity. Histologically, the moderator band was invested in a dense capsule of connective tissue, endocardium that is mainly consisting of three layers; the endothelial layer of simple squamous epithelium, subendothelial layer of loose connective tissue and the subendocardial layer that connects the endocardium with myocardium. Internally, about 4/5 of the core, myocardium is of the cardiac muscle fibers that arranged in bundles of one direction while only about 1/5 is lodged by purkinje cardiomyocytes that were arranged in bundles distributing mainly in two areas within the moderator band; the subendocardial layer beneath the subendothelial connective tissue and myocardium in between the cardiac myocytes bundles. Centrally, a medium-sized artery of thick wall and a very distinct internal elastic lamina was observed running at the center of the band myocardium and is surrounded with the cardiac myocytes bundles.

Gross and microanatomical studies on the moderator bands (septomarginal trabecula) in the heart of mature Dromedary camel (Camelus dromedarius)

The current work was carried out to investigate the gross and microanatomical features of moderator bands (septomarginal trabecula) in camel heart. Ten hearts were collected from healthy mature dromedary camels. Anatomically, the moderator bands were present in both right and left ventricles. In right ventricle, the walls had one muscular moderator band which was extended from the interventricular septum to the opposite ventricular wall especially to the papillary muscle. In left ventricle, there were two bands; one extended from the interventricular septum to the papillary muscles, and the other one was present in various places especially in the apex running as a thin thread-like band across the left ventricular wall. Histological examination revealed that the moderator band consisted of two major layers; the central (core) myocardium and the peripheral endocardium, acting as band capsule. The myocardium had two bundles; the contractile cardiac muscle bundles and the Purkinje fiber bundles. The endocardium consisted of three layers; the endothelial layer of simple squamous epithelium, the subendothelial layer of loose connective tissue and the subendocardial layer, connecting the endocardium with the myocardium.

Left Ventricles of the Mature Camel Heart (Camelus dromedaries) with Special References to the Structure and Distribution of the Purkinje Cardiomyocytes: Microanatomy

The present investigation was performed to clarify the histological features of the left ventricles in the heart of the mature dromedary camel. This investigation was carried out on the left ventricles of six healthy mature camels. Microscopically, the left ventricles is consisted of three major layers or tunics; the internal endocardium, the middle myocardium, and the external epicardium. The endocardium is consisted of three layers; the endothelial layer of simple squamous epithelium, subendothelial layer of loose connective tissue and the subendocardial layer that connecting the endocardium with the myocardium and housing bundles of the purkinje cardiomyocytes; purkinje fibers. The myocardium, is the middle layer of the ventricular wall, is sandwiched between an outer epicardium, that covers the ventricular wall, and an inner endocardium, that lines the chamber, containing two bundles of cardiac fibers; the working cardiac myocytes (myocardiocytes) and the purkinje bundles. The epicardium is the outer most layer of the ventricular wall. This layer is a relatively thin in comparison with the myocardium and is consisted of a subepicardial layer of loose connective tissue which housing many blood vessels, lymph vessels, nerves and adipocytes and mesothelium of simple squamous epithelium.

Study on the Morphohistological Patterns and Functions of Vasdeferens and Spermatophores in Male Fresh Water Crab Spiralothelphusa hydrodroma

The present study describes the morphology and histological functions of the testes and vas deferens of Spiralotelphusa hydrodroma. The morphohistological of this fresh water crab is presented, with a detailed analysis of the histology of the regional structure of the testis and vas deferens. The H-shaped testis is subdivided into three distinct parts: anterior, iintermediate and posterior. The vas deferens is continuous with the posterior part of the testis, ends at the ejaculatory duct , and is subdivided into three distinct regions: proximal, medial and distal. The anterior part of the testis exhibits convoluted lobules including seminiferous tubules. Whereas the intermediate part of the testis has a simple columnar epithelium, the posterior part of the testis has a simple squamous epithelium. In the proximal and medial regions of the vas deferens, there is a simple cubic epithelium, while in the distal region of the vas deferens there is a high columnar epithelium. Spermatophores are first formed in the convoluted proximal region of the vasdeferens and are encapsulated by mainly protein secretions in the distal region. These results suggest that the testis and vas deferens of Spiralotelphusa hydrodroma show similarity to the testis and vasdeferens of other brachyuran crabs except for some slight differences. Spermatophores were observed in both vasdeferens regions suggesting that they participated in the maturation of the spermatozoids preparing the male functionally for fertilization.

Development of the Serosal Mesothelium

Mesothelia in the adult vertebrate are the simple squamous epithelia covering all coelomic organs and body cavities. Until recently, analysis of the generation and differentiative potential of mesothelia in organogenesis has largely focused on development of visceral mesothelium of the heart; the epicardium and its progenitor, the proepicardium. Here, we review emerging data on the development and differentiation of serosal mesothelium, the covering of the gastrointestinal tract. This literature demonstrates that serosal mesothelium is generated through a completely different mechanism than that seen in the heart suggesting that commitment of progenitors to this cell lineage does not follow a common pathway. The differentiative potential of serosal mesothelium is also discussed in comparison to that observed for progeny of the proepicardium/epicardium. In our review of the literature, we point out gaps in our understanding of serosal mesothelial development and that of mesothelial development as a whole.

Vascularización, morfología e histología del ovario en el armadillo Euphractus sexcinctus (Linnaeus, 1758)

SUMMARY Euphractus sexcinctus is a species of armadillo from South America and there are not many studies on its reproductive anatomy. Five corpses of adult females were collected according to the Brazilian Institute of Environment and Renewable Natural Resources (IBAMA) guidelines. The ovaries were dissected and processed for histological examination after standard staining with hematoxylin-eosin. The shape of the ovaries was oval, measuring 7,9 mm in length and width 4,4 mm. There was no central concavity in the ovary as opossed to previous reports on armadillos. The ovaries were covered with simple squamous epithelium and connective tissue rich in collagen fibers. The cortical region presented follicles at various stages of development, with primordial follicles being in clusters. The region containing blood vessels and medullary interstitial cells, and sex cord as described in other species of armadillos. The tertiary follicle oocyte measured 183 ± 18 mm diameter, with a spherical nucleus and dispersed chromatin. The zona pellucida was homogeneous and acellular around the oocyte. Follicles with oocyte groups were not identified. This study demonstrated that ovarian morphology of E. sexcinctus was similar to that of other mammals, but different from other species of armadillos described in other articles.

Thymosin β4 mobilizes mesothelial cells for blood vessel repair

Mesothelium is the simple squamous epithelium covering all abdominal organs and the coeloms in which those organs reside. While the structural characteristics of this cell type were documented a century ago, its potential in development, disease, and wound healing is only now becoming apparent. In the embryo, mesothelia provide vasculogenic cells for the developing heart, lungs, and gut. Furthermore, adult mesothelial cells can be reactivated using thymosin β4 and mobilized to aid in tissue repair. Despite their positive role in development and repair, mesothelia are also susceptible to adhesion and tumor formation. With knowledge that the mesothelium is an important mediator of tissue repair as well as disease, it will be important to identify other factors like thymosin β4 that have the ability to potentiate these cells. Future use of chemical and genetic agents in conjunction with mesothelial cells will lead to enhanced therapeutic potential and mitigation of deleterious outcomes.

Morphological observations of ampullae of lorenzini in Squatina guggenheim and S. occulta (chondrichthyes, elasmobranchii, squatinidae)

We have conducted a morphological study of the ampullae of Lorenzini on two shark species from Squatina Genus. In both species, S. guggenheim and S. occulta, the ampullae were observed like small pores scattered in the head region similar to other species of the Chondrichthyes Class. However, differently of the other species a greatest density of ampullae of Lorenzini was observed along of the body surface. After fixation using 10% formaldehyde, the ampullae were removed and processed for light and scanning electron microscopy. Macroscopically, the two shark species differed by the presence of dorsal spines that appeared from the head to the first dorsal fin in S. guggenheim and were absent in S. occulta. Microscopically, there were no differences between the ampullae of Lorenzini channels in these two species. The wall of the ampulla was formed by a simple squamous epithelium. Bands of connective tissue, hyaline cartilage and collagen fibers were found between the ampulla and the skeletal striated muscle layer. Nerve branches responsible for conducting signal pulses to the central nervous system were visible between the muscle and connective tissue layers. Using scanning electron microscopy and histological analysis, we found that the channels were twisted and positioned parallel to the skin. The inside of the channels contained a large amount of a gelatinous secretion composed by polysaccharides. Therefore, we conclude that the morphological combination of extended distribution of the ampullae of Lorenzini and the body shape may represent an adaptation of these species to their way of life.

Autotaxin, a potent inducer of cell motility and differentiation, is differentially expressed in visceral and parietal mesothelia

The serosal mesothelium is a simple squamous epithelium lining the body cavity. It can be divided into two categories: visceral mesothelium covering abdominal organs including the omentum and parietal mesothelium lining the peritoneal wall. Earlier investigations considered visceral and parietal mesothelia the same cell type. Indeed, these tissues are continuous and share similar expression of mesothelial marker genes. However, we report a microarray analysis of murine visceral and parietal mesothelia where over 35,000 genes were differentially expressed. Specifically, Autotaxin (Atx) was expressed significantly higher in visceral versus parietal mesothelium. Atx is a secreted glycoprotein that is responsible for production of Lysophosphatidic acid (Lpa), promotes cell motility, cell survival, and angiogenesis, and has been identified as an important mediator of tumorigenesis. Here, we demonstrate visceral mesothelium migrates and differentiates into smooth muscle more readily than parietal mesothelium. Addition of Atx to parietal cells induces “visceral‐like” migration and differentiation. Finally, we identified several novel small organic molecule inhibitors of Lpa that repress Atx‐induced motility and differentiation. Importantly, as Atx plays a critical role in tumorigenesis, these inhibitors may represent new therapeutic agents for a variety of cancers including mesothelioma.Grant Funding Source: NIH

Ultrastructural profile of metapleural gland cells of the ant Atta laevigata (F. Smith, 1858) (Formicidae: Attini)

AbstractThe metapleural gland is considered a synapomorphy of ants, and is characterized as a paired structure located at the two postlateral ends of the thorax and secretes substances capable of inhibiting and controlling fungi and bacteria in the fungus garden and inside the nest. This study was aimed at investigating if and which are the ultrastructural differences in the metapleural gland cells of workers (three castes) of Atta laevigata using transmission electron microscopy (TEM). This study revealed the presence of Golgi regions, rough endoplasmic reticulum (lamellar and vesicular shapes), smooth endoplasmic reticulum, mitochondria (elongated, round-shaped), vacuoles, secretion granules with different electron densities, and myelin figures in the cytoplasm of secretory cells, indicating that this gland produces substances composed of proteins, lipids, and polysaccharides (glycogen in major workers). Lipid droplets and secretion granules were found very near to the microvilli, especially in minor workers. The intracellular portion of canaliculi exhibited invaginations that increased the surface area and modified the secretion produced by the secretory cells. In the three castes examined, the gland exhibited a reservoir preceded by a collecting chamber, both lined by a simple squamous epithelium with a cuticular intima. Workers of the three castes of A. laevigata might be involved in the production of secretion mainly composed of proteins with antibiotic properties and, minor workers, may be responsible for producing a wider variety of secretions compared to median and major workers in the colony.

Left Ventricles of the Mature Camel Heart (Camelus dromedaries) with Special References to the Structure and Distribution of the Purkinje Cardiomyocytes:Microanatomy

The present investigation was performed to clarify the histological features of the left ventricles in the heart of the mature dromedary camel. This investigation was carried out on the left ventricles of six healthy mature camels. Microscopically, the left ventricles is consisted of three major layers or tunics; the internal endocardium, the middle myocardium, and the external epicardium. The endocardium is consisted of three layers; the endothelial layer of simple squamous epithelium, sub-endothelial layer of loose connective tissue and the sub-endocardial layer that connecting the endocardium with the myocardium and housing bundles of the purkinje cardiomyocytes; purkinje fibers. The myocardium, is the middle layer of the ventricular wall, is sandwiched between an outer epicardium, that covers the ventricular wall, and an inner endocardium, that lines the chamber, containing two bundles of cardiac fibers; the working cardiac myocytes (myocardiocytes) and the purkinje bundles. The epicardium is the outer most layer of the ventricular wall. This layer is a relatively thin in comparison with the myocardium and is consisted of a sub-epicardial layer of loose connective tissue which housing many blood vessels, lymph vessels, nerves and adipocytes and mesothelium of simple squamous epithelium.

Papillary Muscles in the Heart Ventricles of the Mature Dromedary Camel (Camelus dromedaries) with Special References to the Chordae Tendineae: Gross and Microanatomy

The present investigation was carried out on the papillary muscles of ten healthy mature dromedary camels. Anatomically, the papillary muscles are muscular projections from the walls of the right and left ventricles into their cavities. They are processing many nipples like processes. The apex of each muscle process is attached to cord-like tendons; chordae tendineae. The latter, are string-like in appearance and are sometimes referred to as heart strings that linking the papillary muscles to the tricuspid valve in the right ventricle and the mitral valve in the left ventricle. These cords divided, in turn, into sub branches before attaching to the apex, body and base of the cusp, , preventing eversion of the valve leaflets into the atria during the ventricular contraction. So histologically, there are great invasions of the chordae tendineae to inside the papillary muscles. These chordae tendineae are observed highly branched looked like the tree roots and the finger like projections in between the cardiac muscle fibers within the papillary muscles. Histologically, the papillary muscle is consisting of two major layers; the central myocardium and the peripheral endocardium which act as a capsule. The myocardium has two bundles; the contractile cardiomyocytes bundles and the purkinje cardiomyocytes bundles. The papillary muscles are completely covered externally by a single layer of simple squamous epithelium; endothelium that is reflected from the ventricular endothelium. The latter, is supported by a subendothelial loose connective tissue that is mainly composed of collagen and elastic fibers.

Epidermoid cysts in head and neck: our experiences, with review of literature.

Epidermoid cysts are benign lesions, characterized by cystic spaces lined by simple squamous epithelium (epidermoid cyst), containing skin adnexa ("true" dermoid cyst) or tissues of all three germ layers (teratoid cyst). Head and neck constitute~7% of all cases of epidermoid and dermoid cysts. There is often a diagnostic dilemma with the more common cystic lesions of this region. A retrospective case-series study of histologically proved epidermoid cysts in the head-neck region, from February 2008 to January 2011, in the Department of Otorhinolaryngology and Head-Neck Surgery of a tertiary Government teaching hospital in eastern India. The diagnosis was reached by fine needle aspiration cytology FNAC and subsequent histopathology where feasible. Necessary imaging was done for evaluation and management. A total of 28 cases were analyzed. 5 were female, with a male: female ratio of 4.6. Age range was from 2 to 60years (mean=30). Excision was the preferred treatment in 20 cases (71.4%). Various sites like the submandibular region (5), pinna (5), sublingual region (1), periorbital (6), suprasternal (6), along the anterior border of sternocleidomastoid (1) and glabella (3) were involved, along with an iatrogenic implantation epidermoid cyst in a tracheostomy scar. Some of the interesting cases presenting with clinical dilemma have been emphasized. Epidermoid cysts are relatively less common in the head-neck region, hence are liable to be misdiagnosed. In this case-series, few cases presenting with enough elements of confusion and dilemma are discussed with overall analysis and review of the related literature.

Observations on the anterior testicular ducts in snakes with emphasis on sea snakes and ultrastructure in the yellow‐bellied sea snake, Pelamis platurus

The anterior testicular ducts of squamates transport sperm from the seminiferous tubules to the ductus deferens. These ducts consist of the rete testis, ductuli efferentes, and ductus epididymis. Many histological and a few ultrastructural studies of the squamate reproductive tract exist, but none concern the Hydrophiidae, the sea snakes and sea kraits. In this study, we describe the anterior testicular ducts of six species of hydrophiid snakes as well as representatives from the Elapidae, Homolapsidae, Leptotyphlopidae, and Uropeltidae. In addition, we examine the ultrastructure of these ducts in the yellow-bellied Sea Snake, Pelamis platurus, only the third such study on snakes. The anterior testicular ducts are similar in histology in all species examined. The rete testis is simple squamous or cuboidal epithelium and transports sperm from the seminiferous tubules to the ductuli efferentes in the extratesticular epididymal sheath. The ductuli efferentes are branched, convoluted tubules composed of simple cuboidal, ciliated epithelium, and many species possess periodic acid-Schiff+ granules in the cytoplasm. The ductus epididymis at the light microscopy level appears composed of pseudostratified columnar epithelium. At the ultrastructural level, the rete testis and ductuli efferentes of P. platurus possess numerous small coated vesicles and lack secretory vacuoles. Apocrine blebs in the ductuli efferentes, however, indicate secretory activity, possibly by a constitutive pathway. Ultrastructure reveals three types of cells in the ductus epididymis of P. platurus: columnar principal cells, squamous basal cells, and mitochondria-rich apical cells. This is the first report of apical cells in a snake. In addition, occasional principal cells possess a single cilium, which has not been reported in reptiles previously but is known in some birds. Finally, the ductus epididymis of P. platurus differs from other snakes that have been studied in possession of apical, biphasic secretory vacuoles. All of the proximal ducts are characterized by widening of adjacent plasma membranes into wide intercellular spaces, especially between the principal cells of the ductus epididymis. Our results contribute to a larger, collaborative study of the evolution of the squamate reproductive tract and to the potential for utilizing cellular characters in future phylogenetic inferences.

Microscopic Anatomy of the Lower Respiratory Tract of the Grey Short-Tailed Opossum (Monodelphis domestica)

The respiratory tracts of seven grey short-tailed opossums were histologically examined. Six opossums were prepared by perfusion with buffered formalin. Opossum seven was perfused with gluteraldehyde. Samples taken from the respiratory passages and lungs of specimens 1-6 were stained with haematoxylin and eosin. A mixture of methylene and azure blue was used for specimen 7. The trachea and right and left principal bronchi are lined with a pseudostratified ciliated columnar epithelium with occasional goblet cells. The secondary and tertiary bronchi and the primary and secondary bronchioles are lined by a simple ciliated columnar epithelium. The terminal bronchioles and a portion of the respiratory bronchioles are lined by a simple ciliated cuboidal epithelium. The terminal portion of the respiratory bronchioles and the alveolar ducts are lined with simple squamous epithelium. Alveoli are lined by type I and II pneumocytes. Tracheal glands are present in the tela submucosa. The fibromusculocartilaginous tunic of the trachea consists of c-shaped cartilage rings and the trachealis muscle. A lamina muscularis mucosa begins in the intrapulmonary portion of the principal bronchus and continues into the respiratory bronchioles. Bronchial glands are present in the propria submucosa and tela submucosa of the principal bronchi. The musculocartilaginous tunic is localized to the extrapulmonary portion of the principal bronchus. The bronchial cartilages are irregular shaped plates and limited to the extrapulmonary portion of the principal bronchus. The visceral pleura is a simple squamous mesothelium covering the outer surface of the lung.

Lateral periodontal cyst: report of case and review of the literature

As the lateral periodontal cyst (LPC) is an unusual odontogenic cyst, most papers are single case reports or series with a limited number of cases, with few large series. The aim of this study is to report an additional case of LPC, emphasizing the clinical, radiographic, and histopathological features, differential diagnosis, and review of 264 cases reported in the English-language literature. A 51-year-old male patient presented with a well-delimited, radiolucent, mandibular lesion, located between the roots of the right lower lateral incisor and canine and evidenced during routine radiographic examination. A surgical excision was performed. Microscopically, there was a cystic cavity lined by simple squamous epithelium, compatible with LPC. LPC is an unusual odontogenic cyst and presents a marked predilection for occurring in the mandible between the roots of canines and premolars. Accurate clinical and imaging exams should be performed for a correct approach and diagnosis.

Proximal Testicular Ducts of the Mediterranean Gecko (Hemidactylus turcicus)

The efferent ducts of the Mediterranean Gecko, Hemidactylus turcicus (Gekkonidae) were investigated using light and electron microscopy. The seminiferous tubules unite into a single rete testis tubule. The rete testis divides into 3-4 ductuli efferentes which all drain into the cranial portion of the ductus epididymis. All efferent ducts are most active during the months of December to August. The rete testis is composed of a simple squamous epithelium with bifurcated nuclei and a labyrinthine network of intercellular canaliculi. Ciliated and nonciliated cells are present, and more than one cilium extends from the scattered ciliated cells. The presence of small clear vesicles and widened intercellular canaliculi suggest that cells of the rete testis are responsible for intake of luminal fluids. The ductuli efferentes are composed of a simple cuboidal epithelium consisting of ciliated and nonciliated cells, and ciliated cells are the dominant cell type. During the inactive season the number of lysosomes increases and the cells become spermiophagic. The ductus epididymis is composed of a tall pseudostratified columnar epithelium with relatively scarce basal cells. No evidence for regionalization was observed. The ductus epididymis is highly secretory during the active season with numerous electron-dense secretory granules, whose glycoprotein products are released by merocrine secretion. Basally, the active epididymis has swollen intercellular canaliculi and enlarged cisternae of rough endoplasmic reticulum. During the inactive season the secretory activity decreases and membranous structures and fibrous material are observed within widened intercellular canaliculi apical to the basal cells.

Expression of nestin, mesothelin and epithelial membrane antigen (EMA) in developing and adult human meninges and meningiomas

The spatial and temporal pattern of appearance of nestin, epithelial membrane antigen (EMA) and mesothelin proteins was immunohistochemically determined in the cells of normal developing and adult human meninges and meningiomas. Human meninges developed as two mesenchymal condensations in the head region. The simple squamous epithelium on the surface of leptomeninges developed during mesenchymal to epithelial transformation. Nestin appeared for the first time in week 7, EMA in week 8, while mesothelin appeared in week 22 of development. In the late fetal period and after birth, nestin expression decreased, whereas expression of EMA and mesothelin increased. EMA appeared in all surface epithelial cells and nodules, while mesothelin was found only in some of them. In adult meninges, all three proteins were predominantly localized in the surface epithelium and meningeal nodules. In meningothelial meningiomas (WHO grade I), EMA was detected in all tumor cells except in the endothelial cells, mesothelin characterized nests of tumor cells, while nestin was found predominantly in the walls of blood vessels. The distribution pattern of those proteins in normal meningeal and tumor cells indicates that nestin might characterize immature cells, while EMA and mesothelin appeared in maturing epithelial cells. Neoplastic transformation of these specific cell lineages contributes to the cell population in meningiomas.

Morphology of Testis and Vas Deferens in the Xanthoid Crab, Eriphia Verrucosa (Forskål, 1775) (Decapoda: Brachyura)

The anatomy of the male reproductive organs of the brachyuran crab Eriphia verrucosa is presented, with a detailed analysis of the histology and histochemistry of the regional structure of the testis and vas deferens. The H-shaped testis is subdivided into three distinct parts: anterior, intermediate and posterior. The vas deferens is continuous with the posterior part of the testis, ends at the gonopore, and is subdivided into three distinct regions: proximal, medial and distal. The anterior part of the testis exhibits convoluted lobules including seminiferous tubules. Whereas the intermediate part of the testis has a simple columnar epithelium, the posterior part of the testis has a simple squamous epithelium. In the proximal and medial regions of the vas deferens, there is a simple cubic epithelium, while in the distal region of the vas deferens there is a high columnar epithelium. Spermatophores are first formed in the convoluted proximal region of the vas deferens and are encapsulated by mainly protein secretions in the distal region. These results suggest that the testis and vas deferens of Eriphia show similarity to the testis and vas deferens of other brachyuran crabs except for some slight differences. During formation of the spermatophores in the vas deferens the spermatozoa are prepared for successful fertilization.

Stereological estimation of the surface area and oxygen diffusing capacity of the respiratory stomach of the air‐breathing armored catfish Pterygoplichthys anisitsi (Teleostei: Loricariidae)

The stomach of Pterygoplichthys anisitsi has a thin, translucent wall and a simple squamous epithelium with an underlying dense capillary network. In the cardiac and pyloric regions, most cells have short microvilli distributed throughout the cell surface and their edges are characterized by short, densely packed microvilli. The mucosal layer of the stomach has two types of pavement epithelial cells that are similar to those in the aerial respiratory organs. Type 1 pavement epithelial cells, resembling the Type I pneumocyte in mammal lungs, are flat, with a large nucleus, and extend a thin sheet of cytoplasm on the underlying capillary. Type 2 cells, resembling the Type II pneumocyte, possess numerous mitochondria, a well-developed Golgi complex, rough endoplasmic reticulum, and numerous lamellar bodies in different stages of maturation. The gastric glands, distributed throughout the mucosal layer, also have several cells with many lamellar bodies. The total volume (air + tissue), tissue, and air capacity of the stomach when inflated, increase along with body mass. The surface-to-tissue-volume ratio of stomach varies from 108 cm(-1) in the smallest fish (0.084 kg) to 59 cm(-1) in the largest fish (0.60 kg). The total stomach surface area shows a low correlation to body mass. Nevertheless, the body-mass-specific surface area varied from 281.40 cm(2) kg(-1) in the smallest fish to 68.08 cm(2) kg(-1) in the largest fish, indicating a negative correlation to body mass (b = -0.76). The arithmetic mean barrier thickness between air and blood was 1.52 +/- 0.07 microm, whereas the harmonic mean thickness (tau(h)) of the diffusion barrier ranged from 0.40 to 0.74 microm. The anatomical diffusion factor (ADF = cm(2) microm(-1) kg(-1)) and the morphological O(2) diffusion capacity (D(morphol)O(2) = cm(3) min(-1) mmHg(-1) kg(-1)) are higher in the smallest specimen and lower in the largest one. In conclusion, the structure and morphometric data of P. anisitsi stomach indicate that this organ is adapted for oxygen uptake from air.