The homeostasis of NaCl is critical to complex organisms with closed blood systems. Kidneys regulate this salt excretion by modulating the rapport between glomeruli and tubules. The tubules respond to glomeruli with glomerulotubular balance, whereas glomeruli respond to tubules through tubuloglomerular feedback. These relationships are dynamic, mysterious, and amenable to mathematical analyses.
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Skip to main content. Pathway Medicine. Search form Search. Book navigation Immunology. Cardiovascular Medicine. Respiratory Medicine. Gastrointestinal Medicine. Hematology and Oncology. Musculoskeletal System. Basic Concepts. Genetic Disorders. Glomerulotubular Balance. Overview Glomerulotubular Balance refers to the phenomenon whereby a constant fraction of the filtered load of the nephron is resorbed across a range of Glomerular Filtration Rates GFR.
In other words, if the GFR spontaneously increases, the rate of water and solute resorption in the tubule proportionally increases, thus maintaining the same fraction the filtered load being resorbed. The mechanistic basis of glomerulotubular balance is poorly understood but appears to act completely independently of neuroendocrine regulatory mechanisms and is likely an intrinsic property of the nephron itself.
It seems likely that changes in GFR result in modification of the starling forces in the peritubular capillaries resulting in proportionally increased or decreased total nephronic resorption. Significance Glomerulotubular balance is a critical mechanism which protects distal segments of the nephron from being overloaded in contexts of short-term increases in GFR. Distal segments of the nephron have a very limited capacity to increase tubular resorption of water and solutes; consequently, a large increase in distal flow rates would result in a catastrophic loss of fluid in the urine.
Glomerulotubular balance thus guarantees that any momentarily increased tubular flow is resorbed by proximal segments of the nephron which have significantly greater capacity for resorbing large fluid volumes.
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Glomerulotubular Balance, Tubuloglomerular Feedback, and Salt Homeostasis
In the physiology of the kidney , tubuloglomerular feedback TGF is a feedback system inside the kidneys. Within each nephron , information from the renal tubules a downstream area of the tubular fluid is signaled to the glomerulus an upstream area. Tubuloglomerular feedback is one of several mechanisms the kidney uses to regulate glomerular filtration rate GFR. It involves the concept of purinergic signaling , in which an increased distal tubular sodium chloride concentration causes a basolateral release of adenosine from the macula densa cells. This initiates a cascade of events that ultimately brings GFR to an appropriate level. The kidney maintains the electrolyte concentrations, osmolality, and acid-base balance of blood plasma within the narrow limits that are compatible with effective cellular function; and the kidney participates in blood pressure regulation and in the maintenance of steady whole-organism water volume . Fluid flow through the nephron must be kept within a narrow range for normal renal function in order to not compromise the ability of the nephron to maintain salt and water balance.
Characteristics of Glomerulotubular Balance