Water Influx (water + influx)

Distribution by Scientific Domains

Selected Abstracts

Modelling lake stage and water balance of Lake Tana, Ethiopia

Yirgalem A. Chebud
Abstract The level of Lake Tana, Ethiopia, fluctuates annually and seasonally following the patterns of changes in precipitation. In this study, a mass balance approach is used to estimate the hydrological balance of the lake. Water influx from four major rivers, subsurface inflow from the floodplains, precipitation, outflow from the lake constituting river discharge and evapotranspiration from the lake are analysed on monthly and annual bases. Spatial interpolation of precipitation using rain gauge data was conducted using kriging. Outflow from the lake was identified as the evaporation from the lake's surface as well as discharge at the outlet where the Blue Nile commences. Groundwater inflow is estimated using MODular three-dimensional finite-difference ground-water FLOW model software that showed an aligned flow pattern to the river channels. The groundwater outflow is considered negligible based on the secondary sources that confirmed the absence of lake water geochemical mixing outside of the basin. Evaporation is estimated using Penman's, Meyer's and Thornwaite's methods to compare the mass balance and energy balance approaches. Meteorological data, satellite images and temperature perturbation simulations from Global Historical Climate Network of National Oceanographic and Atmospheric Administration are employed for estimation of evaporation input parameters. The difference of the inflow and outflow was taken as storage in depth and compared with the measured water level fluctuations. The study has shown that the monthly and annually calculated lake level replicates the observed values with root mean square error value of 017 and 015 m, respectively. Copyright 2009 John Wiley & Sons, Ltd. [source]

Molecular Diversity of Vasotocin-Dependent Aquaporins Closely Associated with Water Adaptation Strategy in Anuran Amphibians

M. Suzuki
Anuran amphibians represent the first vertebrates that adapted to terrestrial environments, and are successfully distributed around the world, even to forests and arid deserts. Many adult anurans have specialised osmoregulatory organs, in addition to the kidney (i.e. the ventral pelvic skin to absorb water from the external environments and a urinary bladder that stores water and reabsorbs it in times of need). Aquaporin (AQP), a water channel protein, plays a fundamental role in these water absorption/reabsorption processes. The anuran AQP family consists of at least AQP0-AQP5, AQP7-AQP10 and two anuran-specific types, designated as AQPa1 and AQPa2. For the three osmoregulatory organs, AQP3 is constitutively located in the basolateral membrane of the tight-junctioned epithelial cells, allowing water transport between the cytoplasm of these cells and the neighbouring tissue fluid at all times. On the other hand, AQPs at the apical side of the tight epithelial cells are different among these organs, and are named kidney-type AQP2, ventral pelvic skin-type AQPa2 and urinary bladder-type AQPa2. All of them show translocation from the cytoplasmic pool to the apical plasma membrane in response to arginine vasotocin, thereby regulating water transport independently in each osmoregulatory organ. It was further revealed that, in terrestrial and arboreal anurans, the bladder-type AQPa2 is expressed in the pelvic skin, together with the pelvic skin-type AQPa2, potentially facilitating water absorption from the pelvic skin. By contrast, Xenopus has lost the ability to efficiently produce pelvic skin-type AQPa2 (AQP-x3) because Cys-273 of AQP-x3 and/or Cys-273-coding region of AQPx3 mRNA attenuate gene expression at a post-transcriptional step, presumably leading to the prevention of excessive water influx in this aquatic species. Collectively, the acquisition of two forms of AQPa2 and the diversified regulation of their gene expression appears to provide the necessary mechanisms for the evolutionary adaptation of anurans to a wide variety of ecological environments. [source]

Brain edema in liver failure: Basic physiologic principles and management

Fin Stolze Larsen MD
In patients with severe liver failure, brain edema is a frequent and serious complication that may result in high intracranial pressure and brain damage. This short article focuses on basic physiologic principles that determine water flux across the blood-brain barrier. Using the Starling equation, it is evident that both the osmotic and hydrostatic pressure gradients are imbalanced across the blood-brain barrier in patients with acute liver failure. This combination will tend to favor cerebral capillary water influx to the brain. In contrast, the disequilibration of the Starling forces seems to be less pronounced in patients with cirrhosis because the regulation of cerebral blood flow is preserved and the arterial ammonia concentration is lower compared with that of patients with acute liver failure. Treatments that are known to reverse high intracranial pressure tend to decrease the osmotic pressure gradients across the blood-brain barrier. Recent studies indicate that interventions that restrict cerebral blood flow, such as hyperventilation, hypothermia, and indomethacin, are also efficient in preventing edema and high intracranial pressure, probably by decreasing the transcapillary hydrostatic pressure gradient. In our opinion, it is important to recall that rational fluid therapy, adequate ventilation, and temperature control are of direct importance to controlling cerebral capillary water flux in patients with acute liver failure. These simple interventions should be secured before more advanced experimental technologies are instituted to treat these patients. [source]

Emergency treatment of chemical and thermal eye burns

Ralf Kuckelkorn
ABSTRACT. Chemical and thermal eye burns account for a small but significant fraction of ocular trauma. The speed at which initial irrigation of the eye begins, has the greatest influence on the prognosis and outcome of eye burns. Water is commonly recommended as an irrigation fluid. However, water is hypotonic to the corneal stroma. The osmolarity gradient causes an increased water influx into the cornea and the invasion of the corrosive substance into deeper corneal structures. We therefore recommend higher osmolarities for the initial rinsing to mobilize water and the dissolved corrosives out of the burnt tissue. Universal systems such as amphoteric solutions, which have an unspecific binding with bases and acids, provide a convenient solution for emergency neutralisation. Both conservative anti-inflammatory therapy and early surgical intervention are important to reduce the inflammatory response of the burnt tissue. In most severe eye burns, tenonplasty re-establishes the conjunctival surface and limbal vascularity and prevents anterior segment necrosis. [source]