Filtration and Reabsorption
First of all... let's have a quick re-cap on what basically happens in a kidney through the animation below...
Flash from http://www.kidneypatientguide.org.uk/site/HKWanim.php
Filtration
Filtration is the process whereby (usually passive) transport is triggered through the 'push' of blood flow and pressure. This commonly occurs throughout the entire nephron system especially within the Glomerulous and Bowman's Capsule where water, nitrogenous wastes, glucose, amino acids, vitamins, minerals, bicarbonate ions and hormones. The large amount of plasma that also comes through the Glomerulous is due to the extremely high blood pressure present within this structure.
Reabsorbtion
Occuring more commonly within the nephron system than filtration, this is a form of active transport which takes the the useful substances for the body from the tubules and places them back into the blood filled capillaries.
Within the PROXIMAL COLVOLUTED TUBULE reabsorbtion occurs when pH needs to be maintained and biocarbonate ions are reabsorbed back into the blood stream. Glucose, Amino Acids and Potassium Ions are all benefitial for the body so they are actively transported into the blood as well. Sodium and Chlorine Ions are also moved back into the capillaries so that some salt regulation can occur. On the other end of the scale, substances such as hydrogen ions and toxins are actively secreted from the blood into the tubule.
Within the LOOP OF HENLE, the descending limb allows for the reabsorbtion of water through osmosis whereas the ascending limb allows for the passive and active transport of salts such as sodium to move out of the tubules and be reabsorbed.
The DISTAL CONVOLUTED TUBULE is where the final ajustments are made to the passing urine within the tubule systems. This is where highly selective reabsorption takes place allowing for small adjustments to be made especially between the presence of Potassium and Sodium.
Within the PROXIMAL COLVOLUTED TUBULE reabsorbtion occurs when pH needs to be maintained and biocarbonate ions are reabsorbed back into the blood stream. Glucose, Amino Acids and Potassium Ions are all benefitial for the body so they are actively transported into the blood as well. Sodium and Chlorine Ions are also moved back into the capillaries so that some salt regulation can occur. On the other end of the scale, substances such as hydrogen ions and toxins are actively secreted from the blood into the tubule.
Within the LOOP OF HENLE, the descending limb allows for the reabsorbtion of water through osmosis whereas the ascending limb allows for the passive and active transport of salts such as sodium to move out of the tubules and be reabsorbed.
The DISTAL CONVOLUTED TUBULE is where the final ajustments are made to the passing urine within the tubule systems. This is where highly selective reabsorption takes place allowing for small adjustments to be made especially between the presence of Potassium and Sodium.