Portal de Periódicos da CAPES

Pressure-Flow Characteristics of Crab Gills: Implications for Regulation of Hemolymph Pressure

1990; University of Chicago Press; Volume: 63; Issue: 1 Linguagem: Inglês

10.1086/physzool.63.1.30158154

1937-4267

H. H. Taylor,

Mosquito-borne diseases and control

Flow conductances (resistance−1) ofsaline-perfused gills of Carcinus maenas and Ovalipes catharus varied with transmural pressure (Ptrans, internal pressure minus bath pressure). In the range Ptrans = + 1 to + 4 cmH2O, at constant gillpressure drop, conductance was at a plateau. Below +0.5 cmH2O, conductance fell sharply, and at Prans = −0.5 cmH2O conductance was 67% (Carcinus) and 27% (Ovalipes) of plateau conductance. At Ptrans = −2 cmH2O, conductances fell to only 29% and 9%, respectively, of plateau. In vivo, small changes in branchial chamber pressure or hemolymph pressure could alter branchial conductance. Changes in Ptrans during unilateral ventilatory pauses or reversals would favor perfusion of the forwardly ventilated gills. However, bilateral ventilation changes probably cause only minor changes in Ptrans because of the rigid exoskeleton and incom pressible body fluids. All circulatory pressures contain a hydrostatic component, the mean circulatory filling pressure (MCFP orstatic pressure). Unlike the case in vertebrates, MCFP in the crab's open circulation depends on total body volume (not circulating volume) and on exoskeletal compliance (not total vascular compliance). The gills and branchial chamber linings appear to be the most compliant surface structures in crabs and thus determine MCFP. It is argued that the mean pressure in the lamellar hemocoel must normally be close to MCFP and largely independent of cardiac output. However, MCFP, Ptrans, gill volume, and gill conductance are expected to be very sensitive to change in total internal volume (e.g., osmosis, feeding, urine release, hemorrhage). Mechanisms for long-and short-term control of internal volume and pressure are essential for regulation of respiratory blood flow. Flow rectification was observed in the gills of both species. This property may be associated with the efferent valves and with extensions of the lamellar septum into the marginal canal. This asymmetry could assist unidirectional gill perfusion during venous pressure oscillations generated by movement.