most reabsorption in the kidney occurs in the proximal tubule.
most reabsorption in the kidney occurs in the proximal tubule.
where does most reabsorption in the kidney occur?
proximal tubule
in the kidney, around 250 mmol of calcium ions are filtered into the glomerular filtrate per day. most of this (245 mmol/d) is reabsorbed from the tubular fluid, leaving about 5 mmol/d to be excreted in the urine. this reabsorption occurs throughout the tubule (most, 60-70%, of it in the proximal tubule), except in the thin segment of the loop of henle. circulating parathyroid hormone only influences the reabsorption that occurs in the distal tubules and the renal collecting ducts (but see footnote). a more important effect of pth on the kidney is, however, its inhibition of the reabsorption of phosphate (hpo) from the tubular fluid, resulting in a decrease in the plasma phosphate concentration. phosphate ions form water-insoluble salts with calcium. thus, a decrease in the phosphate concentration of the blood plasma (for a given total calcium concentration) increases the amount of calcium that is ionized. a third important effect of pth on the kidney is its stimulation of the conversion of 25-hydroxy vitamin d into 1,25-dihydroxy vitamin d (calcitriol), which is released into the circulation. this latter form of vitamin d is the active hormone which stimulates calcium uptake from the intestine.
parathyroid hormone
in physiology, splay is the difference between urine threshold (the amount of a substance required in the kidneys before it appears in the urine) and saturation, or t where saturation is the exhausted supply of renal reabsorption carriers. in simpler terms, splay is the concentration difference between a substance's maximum renal reabsorption vs. appearance in the urine. splay is usually used in reference to glucose; other substances, such as phosphate, have virtually no splay at all. splay appears to occur because kidney nephrons do not have the same tubular maximum for glucose (tmg) therefore some nephrons may excrete before others and also because "the maximum reabsorption rate (or tm) cannot be achieved until the amount/min of glucose being presented to the renal tubules is great enough to fully saturate the receptor sites". john field of the american physiological society said "since the splay may occur when the residual nephrons are said to be free of anatomic abnormalities, the possibility exists that changes in the kinetics of glucose reabsorption may have been induced".
splay (physiology)