This chapter introduces the ‘who has what’ in terms of water-breathing respiratory faculties for craniotes. A branchial basket and a ventral heart or hearts that perfuse the branchial region with deoxygenated internal fluid is part of the bauplan of all chordates, including craniotes. Cilia ventilate the branchial region of extant non-craniote chordates, which are also predominantly sessile or planktonic filter feeders. In craniotes, the gills are the main gas exchange organs. They are ventilated by muscular activity and perfused with blood that contains haemoglobin in erythrocytes and flows in the opposite direction to the ventilated water (counter-current model). In spite of major differences in the structure of gills and the ventilatory apparatus among jawless craniotes, cartilaginous fish, and bony fish, the basic push–pull, constant, unidirectional flow respiratory mechanism remains unchanged (of course, with a few notable exceptions). In addition, both the blood and the structure of the gills may reflect adaptations of the respiratory faculty to habitual living conditions.
Features of gas exchange in lungs at rabbits in condition of axoplasma shortage in vagus nerve
