Changes

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.

Sodium is then able to move from the interstial fluid into the blood thanks to a combination of the blood having a low hydrostatic pressure and a high protein osmotic pressure.  These conditions exist thanks to the [[The Formation of the Filtrate by the Glomerular Apparatus- Anatomy & Physiology#Factors Which Determine Selective Filtration|selective filtration]] of water, ions and glucose but the selective obstruction of proteins and promote the reabsorption of water and the associated dissolved ions within it back into the blood.

Sodium is then able to move from the interstial fluid into the blood thanks to a combination of the blood having a low hydrostatic pressure and a high protein osmotic pressure.  These conditions exist thanks to the [[Glomerular Apparatus and Filtration - Anatomy & Physiology#Factors Which Determine Selective Filtration|selective filtration]] of water, ions and glucose but the selective obstruction of proteins and promote the reabsorption of water and the associated dissolved ions within it back into the blood.

===[[Aquaporins of the Kidney and Water Homeostasis - Anatomy & Physiology#The Ability of the Kidney To Alter the Water Content of the Body| Water]]===

===[[Aquaporins of the Kidney and Water Homeostasis - Anatomy & Physiology#The Ability of the Kidney To Alter the Water Content of the Body| Water]]===

===Protein===

===Protein===

Peptide hormones and small amounts of albumin make it through the [[The Formation of the Filtrate by the Glomerular Apparatus- Anatomy & Physiology#Function of Renal Corpuscle|glomerular filtration barrier]] and these need to be reabsorbed.  The reabsorption occurs via '''endocytosis''' in the proximal tubules.  They are then broken down to amino acids in the epithelial cell cytoplasm and move via facilitated diffusion into the interstial fluid.  The reabsorption of protein is usually complete though it is normal to detect small quantities of protein in the urine of some mammals e.g. the dog

Peptide hormones and small amounts of albumin make it through the [[Glomerular Apparatus and Filtration - Anatomy & Physiology#Function of Renal Corpuscle|glomerular filtration barrier]] and these need to be reabsorbed.  The reabsorption occurs via '''endocytosis''' in the proximal tubules.  They are then broken down to amino acids in the epithelial cell cytoplasm and move via facilitated diffusion into the interstial fluid.  The reabsorption of protein is usually complete though it is normal to detect small quantities of protein in the urine of some mammals e.g. the dog

===Primary Active Secretion - Organic Acids and Bases===

===Primary Active Secretion - Organic Acids and Bases===