IGCSE Biology glossary
Collecting duct
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Definition
The final part of the nephron where the permeability of the walls is controlled by ADH (antidiuretic hormone). When the body is dehydrated, ADH increases the permeability of the collecting duct walls, allowing more water to be reabsorbed back into the blood, producing concentrated urine.
What to include in an exam answer
Link the collecting duct to ADH and water reabsorption. More ADH means more permeable walls, more water reabsorbed, less urine produced, and more concentrated urine.
Example in context
Explain why a person who drinks very little water produces a small volume of concentrated urine (3 marks): The blood becomes more concentrated (lower water potential). The pituitary gland releases more ADH. ADH makes the collecting duct walls more permeable to water, so more water is reabsorbed into the blood and less urine of higher concentration is produced.
Related syllabus topic
Excretion in humans