Definitions
• Anuria refers to a total stop of urine production frequently caused by circulatory failure with anoxic damage of the tubular system.
• (Renal plasma) Clearance is a cleaning index for blood plasma passing the kidneys. The efficacy of this cleaning process is directly proportional to the excretion rate for the substance, and inversely proportional to its plasma concentration.
• Diuresis is an increased urine flow (ie, volume of urine produced per time unit).
• Excretion fraction (EF) for a substance is the fraction of its glomerular filtration rate, which passes to and is excreted in the urine.
• ¬Extraction fraction (E) for a substance is the fraction extracted by glomerular filtration from the total amount of substance delivered to the kidney during one passage of the arterial blood plasma.
• Free water clearance is the difference between urine flow and osmolar clearance (see below). The free water clearance is an indicator of the excretion of solute-free water by the kidneys. Excess water is excreted compared to solutes, when free-water clearance is positive. Excess solutes are excreted compared to water, when free-water clearance is negative. – Free water clearance is an estimate of the renal capacity for excretion of solute-free water.
• Glomerular filtration is due to a hydrostatic/colloid osmotic pressure gradient – the Starling forces.
• Glomerular filtration fraction (GFF) is the fraction of the plasma flowing to the kidneys that is ultrafiltered (GFR/RPF). GFF is normally 0.20 or 1/5. – The GFF is reduced during acute glomerulonephritis.
• Glomerulonephritis is an autoimmune injury of the glomeruli of both kidneys.
• Glomerular filtration rate (GFR) is the volume of glomerular filtrate produced per min.
• Glomerular propulsion pressure in the blood of the glomerular capillaries is the hydrostatic minus the colloid osmotic pressure of the blood (ie, 2-3 kPa in a healthy resting person).
• Glomerulo-tubular balance refers to the simultaneous increase in NaCl and water reabsorption in the proximal tubules as a result of an increase in GFR and filtration rate of NaCl. An almost constant fraction of salt and water is thus reabsorbed regardless of the size of GFR.
• Nephron: A nephron consists of a glomerulus, a proximal tubule forming several coils (pars convoluta) before ending in a straight segment (pars recta), the thin part of the Henle loop and a distal tubule also with a pars recta and a pars convoluta.
• The nephrotic syndrome refers to a serious increase in the permeability of the glomerular barrier to albumin, resulting in a marked loss of albumin in the urine. The albuminuria (more than 3 g per day) causes hypoalbuminaemia and generalized oedema.
• Net ultrafiltration pressure is the pressure gradient governing the glomerular filtration – the net result of the so-called Starling forces (see Fig. 25-7).
• Osmolar clearance is the plasma volume cleared of osmoles (solutes) each minute. – Osmolar clearance is also defined as the fictive urine flow that would have rendered the urine isosmolar with plasma. – Osmolar clearance is the difference between the urine flow and the free water clearance, and osmolar clearance estimates the renal capacity to excrete solutes.
• Osmolarity is the amount of osmotically active particles dissolved in a litre of solution.
• Proximal tubule consists of the proximal convoluted tubule and pars recta.
• Renal threshold for glucose is the blood glucose concentration at which the glucose can be first detected in the urine (appearance threshold) or at which the reabsorption capacities of all tubules are saturated (saturation threshold).
• Renal ultrafiltrate is also compared to plasma water, because it is composed like plasma minus proteins. The fraction of one litre of plasma that is pure water is typically 0.94. Thus, the concentration of many substances in the ultrafiltrate, Cfiltr, is equal to Cp/0.94.
• Single effect gradient is a transepithelial concentration gradient between the tubular fluid and the medullary interstitial fluid established at each level of the thick ascending limb by active NaCl reabsorption.
• Tmax refers to the maximal net transfer rate of substance by tubular secretion or reabsorption.
• Tubular passage fraction. The fraction of the amount ultrafiltered of substance passing a cross section of the nephron is the passage fraction. The passage fraction for inulin does not vary at all throughout the nephron. The passage fraction for inulin is one and remains so.
• Tubular reabsorption fraction. The reabsorption fraction is the reverse of the passage fraction (1 minus the passage fraction).
• Tubular reabsorption (active or passive) is the net movement of water and solute from the tubular lumen to the tubule cells and often further on into the peritubular capillary network.
• Tubular secretion (active or passive) represents the net addition