Glomerulotubular balance GTB is defined as the ability of each successive segment of the proximal tubule to reabsorb a constant fraction of glomerular filtrate and solutes delivered to it. For maintenance of GTB the coupling of peritubular blood flow and intratubular fluid flow to the process of glomerular filtration seems to be of functional importance since tubular fluid reabsorption is significantly altered when either or both parameters are experimentally changed. In the case of peritubular blood flow, variations of tubular fluid reabsorption have been ascribed to variations of the mean net colloid osmotic pressure in the peritubular blood and its effects on the paracellular backleak of tubular resorbate. This relationship has, however, been clearly demonstrated only in volume expansion, when GTB is impaired.
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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.