Ultrafiltration is the non-specific filtration of the blood as it enters the Bowman’s capsule of the kidney in which hydrostatic pressure created by the high pressure in the glomerulus (capillaries) forces a liquid against a semi-permeable membrane. Even though glucose is normally filtered and then entirely reabsorbed, some glucose is used by the metabolism of the kidney and therefore the concentration is slightly lower in the renal vein compared to the renal artery It also has a higher partial pressure of CO2 because this is a waste product of metabolism. ![]() Blood leaving the kidney through the renal vein is deoxygenated relative to the renal artery because kidney metabolism requires oxygen. The metabolic activity of the kidney itself also causes a difference between the composition of blood in the renal artery and the renal vein. NOTE: the kidney is the filter of the body - thus the substances that need to be removed from the body are present in higher amounts in the blood vessel entering the kidney (the renal artery). excess salt, absorbed from food in the gut.excess water, produced by cell respiration or absorbed from food in the gut.Other things removed from the blood by the kidney that are not excretory products include: excretory waste products including nitrogenous waste products, mainly urea.betalain pigments in beets and also drugs toxins and other substances that are ingested and absorbed but are not fully metabolised by the body e.g.Substances that are present in HIGHER amounts in the renal artery than the renal vein include: In the renal vein blood leaves the kidney.In the renal artery blood enters the kidney.Arteries carry blood away from the heart veins return blood to the heart. ![]() Due to the relatively small difference in protein concentrations between blood plasma and interstitial fluid and to the short range of electrostatic interactions, the influence of proteins on the distribution of small ions is negligible.Both arteries and veins (in the renal system or anywhere else) are types of blood vessels. On theoretical ground it was concluded: the Donnan distribution is valid, if the size of "free-fluid spaces" is relatively large (r greater than 0.03 micron) compared with the rather short range of electrostatic interactions (approximately 0.8 nm). The ion distribution between vascular and interstitial compartments was found to correspond to the Donnan equilibrium. The samples were analyzed for sodium, potassium, calcium, chloride, total protein, and protein fractions. Subcutaneous interstitial fluid samples were collected in rats by the implanted capsule and by the liquid paraffin cavity techniques. Because no adequate explanation has been provided for the discrepancy, we attempted to study the question 1) by measuring ion and protein concentration in the plasma and in the interstitial fluid samples, and 2) by constructing a theoretical model for ion distribution. Electrolyte concentration values in interstitial fluid samples that have been reported by a number of authors were markedly different from those of a hypothetical ultrafiltrate of plasma.
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