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Reabsorption and Secretion Along the Proximal Tubule - Anatomy & Physiology (view source)
Revision as of 16:29, 3 September 2008
, 16:29, 3 September 2008→[[Sodium Homeostasis - Physiology#Main Sites of Reabsorption| Sodium]]
===[[Sodium Homeostasis - Physiology#Main Sites of Reabsorption| Sodium]]===
===[[Sodium Homeostasis - Physiology#Main Sites of Reabsorption| 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]].
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 their 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 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]]===