The Microvascular Anatomy of the Trachea in Adult Xenopus laevis Daudin (Lissamphibia; Anura): Scanning Electron Microscopy of Vascular Corrosion Casts and Correlative Light Microscopy

Abstract

Studies on the amphibian respiratory tract microvascular anatomy are few and contradictory. Using scanning electron microscopy of vascular corrosion casts, correlative light microscopy of paraplast-embedded Goldner-stained serial tissue sections, and three-dimensional morphometry, we studied the topographic microvascular anatomy in the trachea of the adult South African Clawed Toad, Xenopus laevis Daudin. Histomorphology showed that the cartilaginous portion of the trachea contained irregularly shaped hyaline cartilage plates in its cranial and caudal portions and C-shaped hyaline cartilage rings in the middle portion. Tracheal cartilages formed large continuous plates on the ventral circumference, numerous small discontinuous plates on the dorsal circumference, and large vertical plates on the caudolateral circumference. The muscular portion of the trachea consisted of bands of smooth muscle that joined the free ends of cartilage plates. The supply of the trachea was via pulmonal artery-tracheobronchial trunk artery-tracheobronchial artery-tracheal artery. The subepithelial capillary network consisted of rectangular meshes which are in the area of the tracheal cartilages located between the cartilages and the respiratory epithelium. Small tracheal veins merged into a single tracheal vein that emptied into the pulmonary vein. Because of its dense subepithelial capillary network and its drainage into the pulmonal vein, the trachea could actively take part in respiration.