The process of excretion is vital for maintaining a constant internal environment. In the human kidney, selective reabsorption in the proximal convoluted tubule (PCT) and regulated water reabsorption in the collecting duct both play key homeostatic roles.
Describe the similarities and differences between the selective reabsorption of water and solutes in the PCT and the regulated reabsorption of water in the collecting duct.
A patient's renal performance can also be monitored by measuring their blood urea nitrogen (BUN) or plasma urea concentration. Urea is a nitrogenous waste product excreted by the kidneys.
Identify two patient-specific physiological factors (other than kidney disease) that must be considered when interpreting blood urea concentration, and explain how each factor affects blood urea levels.
Under healthy conditions, large macromolecules are prevented from entering the nephron lumen. Explain why the presence of high levels of the plasma protein albumin in the urine (proteinuria) is an indicator of glomerular damage.
17 exam-style questions on OCR A A Level Biology Excretion as an example of homeostatic control. Each one has a worked solution and a mark scheme showing where the marks go.