2.77B Selective Reabsorption of Glucose (Edexcel IGCSE Biology)

Reabsorption of glucose

• After the glomerular filtrate enters the Bowman’s Capsule, glucose is the first substance to be reabsorbed at the proximal (first) convoluted tubule
• This takes place by active transport
• The nephron is adapted for this by having many mitochondria to provide energy for the active transport of glucose molecules
• Reabsorption of glucose cannot take place anywhere else in the nephron as the gates that facilitate the active transport of glucose are only found in the proximal convoluted tubule
• In a person with a normal blood glucose level, there are enough gates present to remove all of the glucose from the filtrate back into the blood
• People with diabetes cannot control their blood glucose levels and they are often very high, meaning that not all of the glucose filtered out can be reabsorbed into the blood in the proximal convoluted tubule
• As there is nowhere else for the glucose to be reabsorbed, it continues in the filtrate and ends up in the urine
• This is why one of the first tests a doctor may do to check if someone is diabetic is to test their urine for the presence of glucose

Diagram showing reabsorption in the nephron