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: 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. However after Tmax all the nephrons are at and above full capacity and therefore after this point any increase in filtered glucose is demonstrated linearly with that excreted. The Tmax 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 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.