lung morphology trait blood-air barrier morphology trait alveolar-capillary membrane morphology trait alveolocapillary membrane morphology trait alveolar-capillary barrier morphology trait Trait.ontology VT:0002324 Any measurable or observable characteristic related to the shape, structure, color, or pattern of the membrane between the capillary blood and alveolar air, comprised of the alveolar epithelium and the capillary epithelium and their adherent basement membranes and epithelial cell cytoplasm.