Ultramorphology of the ventriculus of nectarivorous, granivorous and omnivorous species of passerine birds

The objective of this study was to investigate the effect of disparate diets on the ventriculi of three species of similar sized granivorous, nectarivorous and omnivorous passerine birds. A total of twelve birds were captured with mist net under license and ventriculi from these birds were processed for light and electron microscopy. Nectarivorousventriculus had thin, poorly developed muscle and sac-like in shape while the granivorous gizzard had the thick, well developed muscle with the classical shape of biconvex lens and the omnivorous gizzard was intermediate. The wall of the ventriculus consisted of mucosal, submucosal , muscularis and inconspicuous serosal layers. Tunica muscularis, the most prominent layer of the wall was thickest in granivore, thinnest in nectarivore , and intermediate in omnivore. The mucosal glands were individual, tubular units with slightly expanded basal ends, demarcated from each other by dense connective tissue and opened individually into the lumen of the organ. Each glandular unit consisted of basal, chief, endocrine, neck and surface epithelial cells.The chief cells of the glandular units produced the "tubular” portion of the cuticle while the neck and surface epithelial cells produced the "surface” portion of the cuticle and the merger of these two portions formed the gastric cuticle, a protein mucopolysaccharide complex. The overlaying gastric cuticle (luminal cuticle) of the ventriculus was hard, tough, and sieve-like in the granivore, soft and jelly-like in the nectarivore and intermediate in the omnivore. The structural adaptations of the ventriculi of these three species to their various diets are discussed. There is need for more studies to be done on composition and functional morphology of the cuticle in aves.Keywords: Morphology, Ventriculus, Gizzard, Passerine Bird

Histomorphology of the proventriculus of three species of Australian passerines: Lichmera indistincta, zosterops lateralis and poephila guttata

Histomorphology of the proventriculi of nectarivorous, granivorous and omnivorous passerines was studied. The proventriculus consisted of mucosal, submucosal, muscularis and serosal layers. Proventricular wall was thickest in omnivore, thinnest in granivore and intermediate in nectarivore. The openings of mucosal glands had a single spiral-like fold of mucosa in the omnivorous Silvereye, 2-3 spirals in the granivorous Zebra finch and 4-5 spirals in the nectarivorous Brown honeyeater. The mucosal glands were arranged in a uniform row in the wall of the organ and opened individually via a primary duct to the lumen of the proventriculus. The surface epithelial cells of the tunica mucosa contained secretory cells and the proventricular glands contained endocrine, neck and oxynticopeptic cells. The ultrastructural features of the oxynticopeptic cells changed from the oral to the aboral portion of the gland. In the oral region, the cytoplasm presented numerous, smaller (600-900 nm) homogenously dense zymogen secretory vesicles and larger (0.8-2.3 μm) pale floccular, tubular, mucin-like secretory granules, few small mitochondria and RER while in the aboral portion of the gland, the cytoplasm presented numerous, large mitochondria with closely packed cristae, secondary lysosome and infolding of the basal and apical cell membrane. The tunica sub mucosa was thin with occasional large blood vessels. The tunica muscularis consisted of inner longitudinal, middle circular and outer longitudinal layers. The external tunica serosa contained large bundles of myelinated and unmyelinated axons that were possibly branches of the intestinal nerve. The structural adaptations of the proventriculi of these three species to their various diets are discussed