<P> The four mechanisms used to create and process the filtrate ( the result of which is to convert blood to urine ) are filtration , reabsorption , secretion and excretion . Filtration occurs in the glomerulus and is largely passive : it is dependent on the intracapillary blood pressure . About one - fifth of the plasma is filtered as the blood passes through the glomerular capillaries ; four - fifths continues into the peritubular capillaries . Normally the only components of the blood that are not filtered into Bowman 's capsule are blood proteins , red blood cells , white blood cells and platelets . Over 150 liters of fluid enter the glomeruli of an adult every day : 99 % of the water in that filtrate is reabsorbed . Reabsorption occurs in the renal tubules and is either passive , due to diffusion , or active , due to pumping against a concentration gradient . Secretion also occurs in the tubules and is active . Substances reabsorbed include : water , sodium , chloride , glucose , amino acids , lactate , magnesium , calcium , phosphate , uric acid , and bicarbonate . Substances secreted include urea , creatinine , potassium , hydrogen , and uric acid . Some of the hormones which signal the tubules to alter the reabsorption or secretion rate , and thereby maintain homeostasis , include ( along with the substance affected ) antidiuretic hormone ( water ) , aldosterone ( sodium , potassium ) , parathyroid hormone ( calcium , phosphate ) , atrial natriuretic peptide ( sodium ) and brain natriuretic peptide ( sodium ) . A countercurrent system in the renal medulla provides the mechanism for generating a hypertonic interstitium , which allows the recovery of solute - free water from within the nephron and returning it to the venous vasculature when appropriate . </P>
<P> The four mechanisms used to create and process the filtrate ( the result of which is to convert blood to urine ) are filtration , reabsorption , secretion and excretion . Filtration occurs in the glomerulus and is largely passive : it is dependent on the intracapillary blood pressure . About one - fifth of the plasma is filtered as the blood passes through the glomerular capillaries ; four - fifths continues into the peritubular capillaries . Normally the only components of the blood that are not filtered into Bowman 's capsule are blood proteins , red blood cells , white blood cells and platelets . Over 150 liters of fluid enter the glomeruli of an adult every day : 99 % of the water in that filtrate is reabsorbed . Reabsorption occurs in the renal tubules and is either passive , due to diffusion , or active , due to pumping against a concentration gradient . Secretion also occurs in the tubules and is active . Substances reabsorbed include : water , sodium , chloride , glucose , amino acids , lactate , magnesium , calcium , phosphate , uric acid , and bicarbonate . Substances secreted include urea , creatinine , potassium , hydrogen , and uric acid . Some of the hormones which signal the tubules to alter the reabsorption or secretion rate , and thereby maintain homeostasis , include ( along with the substance affected ) antidiuretic hormone ( water ) , aldosterone ( sodium , potassium ) , parathyroid hormone ( calcium , phosphate ) , atrial natriuretic peptide ( sodium ) and brain natriuretic peptide ( sodium ) . A countercurrent system in the renal medulla provides the mechanism for generating a hypertonic interstitium , which allows the recovery of solute - free water from within the nephron and returning it to the venous vasculature when appropriate . </P>
where does most absorption occur in the nephron
where does most absorption occur in the nephron
renal tubules
renal tubules