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Renal disorders
Published in Rachel U Sidwell, Mike A Thomson, Concise Paediatrics, 2020
Rachel U Sidwell, Mike A Thomson
The countercurrent mechanism ensures a concentrated environment surrounding the distal collecting duct and thus water is reabsorbed at this point (the amount dependent on ADH status), resulting in more concentrated urine.
Method of Extraction
Published in Ravindra Kumar Pandey, Shiv Shankar Shukla, Amber Vyas, Vishal Jain, Parag Jain, Shailendra Saraf, Fingerprinting Analysis and Quality Control Methods of Herbal Medicines, 2018
Ravindra Kumar Pandey, Shiv Shankar Shukla, Amber Vyas, Vishal Jain, Parag Jain, Shailendra Saraf
Exhaustive extraction is defined as the complete removal of the desired extractive substances from the drug material. The skeletal material of the drug plant remains behind. The objective is a quantitative extraction which can be achieved in various ways. In percolation, the drug plant material is exhaustively extracted by fresh solvent. Only fresh solvent is used and the extraction consumes a large quantity of it and takes a long time. We speak of re-percolation when the drug is first extracted with fresh solvent and then some of the percolate is used for exhaustive extraction by stage wise concentration in another percolator. Continuous countercurrent extraction is a process in which fresh drug plant material is brought into contact with loaded/charged solvent at the same time as fresh solvent is being brought into contact with already pre-extracted drug (Sasidharan, 2011). Percolation is as an effective tool for the extraction of herbals as follows: Quantity of menstruumDiffusion constant of the drug into menstruumDiffusion constant of menstruum into drug
Importance of the Microcirculation to Intestinal Secretion
Published in T. S. Gaginella, Regulatory Mechanisms — in — Gastrointestinal Function, 2017
There is evidence pro and con for the existence of effective countercurrent mechanisms in the villus.3272 It is likely that countercurrent exchange does occur, but the existence of countercurrent multiplication is less likely.73 Countercurrent exchange occurs when substances diffuse between the arteriole and capillaries or venule, and the direction of diffusion is determined by which vascular segment has the higher concentration. Countercurrent exchange, coupled with absorption of solutes in hypertonic solutions by the mucosa, may also create a hypertonic environment within the villus. Oxygen is shunted away from the villous tip, thus reducing metabolism and predisposing the cells at the tip to injury and the tissue to rupture. Molecules that are formed in or absorbed by the epithelium (e.g., or Na+) would tend to recycle within the villus, thus increasing their tendency for back-secretion, but, also, they may provide a driving force for H20 absorption through an increase in osmotic pressure. Accumulation of CO2 or may als° affect NaCl transport by altering the exchange between and Cl” and Na+ and H+ 7475 Countercurrent exchange also may damp sudden changes in villus osmolality when markedly anisotonic solutions are present in the lumen.
In vitro α-glucosidase inhibition by Brazilian medicinal plant extracts characterised by ultra-high performance liquid chromatography coupled to mass spectrometry
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2022
Mariacaterina Lianza, Ferruccio Poli, Alan Menezes do Nascimento, Aline Soares da Silva, Thamirys Silva da Fonseca, Marcos Vinicius Toledo, Rosineide Costa Simas, Andréa Rodrigues Chaves, Gilda Guimarães Leitão, Suzana Guimarães Leitão
Countercurrent chromatography separations were performed on a P.C. Inc. (Potomac, MD) apparatus equipped with a triple polytetrafluoroethylene multi-layer coil (15 mL + 80 mL + 280 mL, 1.6 mm i.d.) equilibrated by a counterweight. The rotation speed is adjustable from 0 to 1000 rpm. The 80-mL coil was used in all experiments. The solvents were pumped with a HPLC Solvent Delivery System Model M-45 Waters (Milford, MA) and the fractions were collected in a Super Fraction Collector SF-2120 Advantec MFS Inc. (Tokyo, Japan). The solvent systems tests were performed as follows: small amounts of a sample extract were dissolved in a test tube containing a two-phase solvent system. After shaking and allowing compounds’ partition between the two phases, equal aliquots of each phase were spotted individually on silica gel TLC plates to determine the distribution coefficients (KD) by visual inspection. Solvent systems used in all separations by CCC were prepared in a separatory funnel at room temperature. After the equilibrating, the two phases were separated and degassed by sonication for 5 min. In each run, a CCC column was first filled with the stationary phase, after setting the rotation, the mobile phase was pumped in. Samples were dissolved in equal volumes of phases and were injected after the hydrodynamic equilibrium inside the column was reached.
Human cold habituation: Physiology, timeline, and modifiers
Published in Temperature, 2022
Beau R. Yurkevicius, Billie K. Alba, Afton D. Seeley, John W. Castellani
The physiological responses of the pearl divers of Korea (Haenyeo) and Japan (Ama) are the best example of adaptations to the chronic declines in core and skin temperature experienced during occupational cold water exposure. These women dive year-round, with average water exposures ranging from 40 min in 28°C in the summer, to 15 min in 10°C in the winter, repeated 2–3 times over the course of a day. Classical divers had very little protection from the cold water, wearing only a cotton bathing suit and therefore had no external insulation from the environment. Due to this lack of external protection, the Ama have been reported to have several adaptations to help protect them from the cold. In the winter, the divers show a 30% higher basal metabolic rate when tested in thermoneutral conditions, and show a suppressed shivering response when immersed in cold water [87–89]. The divers have been reported to have increased tissue insulation, yet are able to maintain a higher blood flow in the lower arms and hands with less heat loss while fully immersed. The authors suggest this is due to “a more efficient countercurrent heat exchange system in the limbs” through which blood may be precooled before reaching the periphery. When only the hand is immersed, the Ama demonstrate a lower hand skin blood flow, yet show a slower reduction in muscle temperature in the lower arm compared to non-divers, thus giving more evidence to a redirection of skin and muscle blood flow [88].
Two novel forms of ERG oscillation in Drosophila: age and activity dependence
Published in Journal of Neurogenetics, 2018
Atsushi Ueda, Scott Woods, Ian McElree, Tristan C. D. G. O’Harrow, Casey Inman, Savantha Thenuwara, Muhammad Aftab, Atulya Iyengar
The countercurrent apparatus used for negative geotaxis and phototaxis assays was originally developed by Benzer (1967). A dim red light in the room facilitated assay operation. Between 7 and 40 flies were loaded into the starting tube of a four-tube countercurrent apparatus. For phototaxis assays, the apparatus was placed horizontally in a light box, with an LED strip light (SuperNight 5050 LEDs; Ebestrade, Portland, OR) placed ∼2 cm from the apparatus. For negative geotaxis assays, the apparatus was positioned vertically. To start each round of taxis, the apparatus was ‘banged down’ to settle the flies. The flies were allowed to move to the opposite tube for 20 s, after which the opposite tube was advanced to the next tube of the apparatus. After three rounds, the number of flies able to successfully traverse to the opposite tube zero, one, two or three times was recorded. The phototaxis and negative geotaxis indices were computed by finding the average number of tubes traversed by flies of a given age, reared at a specified temperature.