Title: Reabsorption and Secretion Along the Proximal Tubule - Anatomy & Physiology - WikiVet English
Headings: Reabsorption and Secretion Along the Proximal Tubule - Anatomy & Physiology
A Tribute to Nick Short
Reabsorption and Secretion Along the Proximal Tubule - Anatomy & Physiology
Contents
Introduction to Reabsorption
Proportion of Filtered Substances Reabsorbed in the Proximal Tubule
Epithelial Transport
Ions and Compounds
Sodium
Water
Potassium
Urea
Glucose
T Max and Splay
The Kidneys Role In Glucose Regulation
The Secretion of H+ and the Reabsorption of HCO3-
Reabsorption of HCO3-
Protein
Primary Active Secretion - Organic Acids and Bases
Calcium
Revision

Content: It is reabsorbed using a co-transporter with sodium. The realisation of the 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 sodium/potassium ATPase which keeps sodium concentrations within the epithelial cells low this giving the sodium in the lumen a high potential energy. Glucose is then passively transported out of the epithelial cells across the basolateral membrane. 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
At approximately three times the normal levels the kidneys begin to approach the maximum possible reabsorption levels this is termed Tmax and is where the entire length of all the proximal tubules of all the nephrons of the kidney are working at maximum capacity. Prior to this point the amount of glucose excreted does not increase linearly with the amount filtered. This is because some nephrons have longer proximal tubules than others so although some may be overcome and therefore allowing glucose to be excreted others are managing to fully reabsorb the glucose along their length. This results in what is termed splay.