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==Introduction to Reabsorption==

==Introduction to Reabsorption==

===Sodium===

===Sodium===

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]].

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 chloride or together with another product such as glucose or AA using a [[Transport Proteins - Physiology#Co-Transporters|co-transporter]] by secondary active co-transport.

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 three sodium ions from the cell and pumps two potassium ions back in.  This creates a high concentration of potassium within the cell but this is corrected by 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 [[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.

Sodium is then able to move from the interstial fluid into the blood due to the low hydrostatic pressure within the capillaries and a high protein osmotic pressure.  These conditions are caused by 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]]===

Use the [[Reabsorption and Secretion Along the Proximal Tubule - Renal Flash Cards - Anatomy & Physiology|flash card revision resource]] for this section to test yourself.

Use the [[Reabsorption and Secretion Along the Proximal Tubule - Renal Flash Cards - Anatomy & Physiology|flash card revision resource]] for this section to test yourself.

 

[[Category:Urinary System]]

[[Category:Urine Production]]

[[Category:Bullet Points]]