Why is reabsorption important in the kidneys

Namely filtration, reabsorption, secretion, and excretion. Reabsorption in the nephron may be either a passive or active process, and the specific permeability of the each part of the nephron varies considerably in terms of the amount and type of substance reabsorbed. The mechanisms of reabsorption into the peri-tubular capillaries include:. These processes involve the substance passing though the luminal barrier and the basolateral membrane, two plasma membranes of the kidney epithelial cells, and into the peri-tubular capillaries on the other side.

Some substances can also pass through tiny spaces in between the renal epithelial cells, called tight junctions. As filtrate passes through the nephron, its osmolarity ion concentration changes as ions and water are reabsorbed.

Finally, in the distal convoluted tubule and collecting duct, a variable amount of ions and water are reabsorbed depending on hormonal stimulus. The final osmolarity of urine is therefore dependent on whether or not the final collecting tubules and ducts are permeable to water or not, which is regulated by homeostasis.

Note that the kidneys filter much more fluid than the amount of urine that is actually excreted about 1. This is essential for the kidneys to rapidly remove waste and toxins from the plasma efficiently. Reabsorption is the movement of water and solutes from the tubule back into the plasma. Reabsorption of water and specific solutes occurs to varying degrees over the entire length of the renal tubule. Bulk reabsorption, which is not under hormonal control, occurs largely in the proximal tubule.

At the same time, waste ions and hydrogen ions pass from the capillaries into the renal tubule. This process is called secretion. The secreted ions combine with the remaining filtrate and become urine. The urine flows out of the nephron tubule into a collecting duct. It passes out of the kidney through the renal pelvis, into the ureter, and down to the bladder.

The nephrons of the kidneys process blood and create urine through a process of filtration, reabsorption, and secretion. Nitrogenous wastes excreted in urine include urea, creatinine, ammonia, and uric acid. Ions such as sodium, potassium, hydrogen, and calcium are also excreted. Download Nephrons Lab Activity. See more from our free eBook library. The Body Online. Urinary System Structures.

Give It Up for the Kidneys.