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Reabsorption and Secretion Along the Proximal Tubule - Anatomy & Physiology (view source)
Revision as of 16:34, 3 September 2008
, 16:34, 3 September 2008→Filtration and Reabsorption
===[[Glucose Homeostasis - Physiology| Glucose]]===
===[[Glucose Homeostasis - Physiology| Glucose]]===
Glucose is a small molecule and so it is filtered in the same concentrations as are found in plasma which is approximately 5mmol/l. Reabsorption of glucose can only occur in the proximal tubule and occurs regardless of the concentration gradient as it is completed via [[Active Transport - Physiology#Secondary Active Transport|secondary active transport]]. It is reabsorbed using a [[Transport Proteins - Physiology#Co-Transporters|co-transporter]] with [[Sodium Homeostasis - Physiology|sodium]]. The realisation of the [[Active Transport - Physiology#Development of Potential Energy|potential energy]] produced from sodium moving from an area of high concentration to an area of low concentration is enough energy to transport glucose across the membrane into the epithelial cells. The energy technically comes from the utilisation of ATP by the [http://w01.rvcwiki.wf.ulcc.ac.uk/images/e/ef/NaKATPaseA%2BP.jpg sodium/potassium] [[Transport Proteins - Physiology#ATPases|ATPase]] which keeps sodium concentrations within the epithelial cells low this giving the sodium in the lumen a high potential energy.
Glucose is a small molecule and so it is filtered in the same concentrations as are found in plasma which is approximately 5mmol/l. Reabsorption of glucose can only occur in the proximal tubule and occurs regardless of the concentration gradient as it is completed via [[Active Transport - Physiology#Secondary Active Transport|secondary active transport]]. It is reabsorbed using a [[Transport Proteins - Physiology#Co-Transporters|co-transporter]] with [[Sodium Homeostasis - Physiology|sodium]]. The realisation of the [[Active Transport - Physiology#Development of Potential Energy|potential energy]] produced from sodium moving from an area of high concentration to an area of low concentration is enough energy to transport glucose across the membrane into the epithelial cells. The energy technically comes from the utilisation of ATP by the [http://w01.rvcwiki.wf.ulcc.ac.uk/images/e/ef/NaKATPaseA%2BP.jpg sodium/potassium] [[Transport Proteins - Physiology#ATPases|ATPase]] which keeps sodium concentrations within the epithelial cells low this giving the sodium in the lumen a high potential energy.
It is normal that reabsorption is fully completed in the first half of this tubule however as the plasma concentration of glucose increases more of the tubule will be utilised to reabsorb the glucose. Concentrations of double the normal levels are required for glucose to appear in the urine and the concentration where glucose can first be detected is termed the '''renal threshold for glucose'''.
It is normal that reabsorption is fully completed in the first half of this tubule however as the plasma concentration of glucose increases more of the tubule will be utilised to reabsorb the glucose. Concentrations of double the normal levels are required for glucose to appear in the urine and the concentration where glucose can first be detected is termed the '''renal threshold for glucose'''.
===T Max and Splay===
=====T Max and Splay=====
At approximately three times the normal levels the kidneys begin to approach the maximum possible reabsorption levels this is termed '''T<sub>max</sub>''' and is where the entire length of all the proximal tubules of all the nephrons of the kidney are working at maximum capacity.
At approximately three times the normal levels the kidneys begin to approach the maximum possible reabsorption levels this is termed '''T<sub>max</sub>''' and is where the entire length of all the proximal tubules of all the nephrons of the kidney are working at maximum capacity.
The '''T<sub>max</sub>''' for a 20Kg dog is approximately 170mg per minute or 220g per 24 hour period. The normal amount of glucose filtered in 24 hours should be 60g.
The '''T<sub>max</sub>''' for a 20Kg dog is approximately 170mg per minute or 220g per 24 hour period. The normal amount of glucose filtered in 24 hours should be 60g.
===The Kidneys Role In Glucose Regulation===
=====The Kidneys Role In Glucose Regulation=====
The kidneys do not really regulate plasma glucose but their main aim is to preserve this valuable nutrient. It is only at very high levels which the kidneys play a role in helping to prevent any further rises in glucose via excretion.
The kidneys do not really regulate plasma glucose but their main aim is to preserve this valuable nutrient. It is only at very high levels which the kidneys play a role in helping to prevent any further rises in glucose via excretion.