Changes

===Sodium===

===Sodium===

The majority (70%) of sodium is reabsorbed in the [[Proximal Tubule - Anatomy & Physiology| proximal tubule.]]  It is reabsorbed into the cytosol of the epithelial cells either alone by [[Diffusion - Physiology| diffusion]] through [[Transport Proteins - Physiology#Diffusion Through Water Filled Protein Channels|ion channels]] followed by water and chlorine or together with another product using a [[Transport Proteins - Physiology#Co-Transporters|co-transporter]].   

The majority (70%) of sodium is reabsorbed in the [[Reabsorption and Secretion Along the Proximal Tubule - Anatomy & Physiology| proximal tubule.]]  It is reabsorbed into the cytosol of the epithelial cells either alone by [[Diffusion - Physiology| diffusion]] through [[Transport Proteins - Physiology#Diffusion Through Water Filled Protein Channels|ion channels]] followed by water and chlorine or together with another product using a [[Transport Proteins - Physiology#Co-Transporters|co-transporter]].   

To maintain the concentration gradients and allow the diffusion to continue it is essential that sodium is not allowed to build up within the cell.  This is the job of the sodium/potassium [[Transport Proteins - Physiology#ATPases|ATPase Pump]] and is an example of [[Active Transport - Physiology#Primary Active Transport|primary active transport]].  This pump removes sodium from the cell and puts potassium in.  This creates a high concentration of potassium within the cell but this is corrected because there are also potassium ion channels in the basolateral membrane which allow potassium to diffuse back into the interstitium.  Because both sodium and potassium are leaving the cell the net effect is that the tubular cells are negatively charged.  This creates an electro gradient which further increases sodium uptake from the cells.  The combined electrochemical gradient is very large allowing for great amounts of sodium to be reabsorbed.

To maintain the concentration gradients and allow the diffusion to continue it is essential that sodium is not allowed to build up within the cell.  This is the job of the sodium/potassium [[Transport Proteins - Physiology#ATPases|ATPase Pump]] and is an example of [[Active Transport - Physiology#Primary Active Transport|primary active transport]].  This pump removes sodium from the cell and puts potassium in.  This creates a high concentration of potassium within the cell but this is corrected because there are also potassium ion channels in the basolateral membrane which allow potassium to diffuse back into the interstitium.  Because both sodium and potassium are leaving the cell the net effect is that the tubular cells are negatively charged.  This creates an electro gradient which further increases sodium uptake from the cells.  The combined electrochemical gradient is very large allowing for great amounts of sodium to be reabsorbed.