Written for this site from the class slides, with textbook page references for each statement. The chapter is on pages 768–778 of the course textbook. Image credits are on slide 16.
Excretion removes waste products of metabolism, such as urea. Osmoregulation controls the osmotic concentration of body fluids, measured in osmol L−1. The kidney does both: it leaves wastes in the urine and varies how much water it reabsorbs.
High pressure in the glomerulus forces plasma through fenestrated capillaries, the basement membrane and slits between podocytes into Bowman’s capsule. Cells and proteins stay behind. In the proximal convoluted tubule, cells with microvilli and many mitochondria reabsorb all the glucose, amino acids and most salt and water, leaving urea and toxins in the filtrate.
The ascending limb actively pumps Na+ into the medulla but does not let water out, so the medulla becomes very concentrated. This lets water be drawn out of the collecting ducts later.
Osmoreceptors in the hypothalamus detect concentrated blood, and the pituitary secretes more ADH. ADH causes vesicles carrying aquaporins to fuse with the membrane of collecting duct cells, so more water is reabsorbed. When blood is dilute, ADH falls and aquaporins are taken back into vesicles.
Arterioles dilate or constrict to send blood where it is needed. In vigorous exercise flow to skeletal muscle rises about twentyfold while flow to the gut and kidneys falls; brain flow stays nearly constant. In sleep, flow to muscle falls.
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A printable worksheet covering all five statements, from quick recall to data questions and a longer answer. It has 30 marks and takes about 30 minutes, or you can do one section at a time.
Your teacher has the mark scheme.
You will need: Dialysis tubing, mix of starch and glucose, water, beaker, iodine solution, glucose test strips
Safety: Eye protection when using iodine. Wipe up spills.
Carry this out with your teacher's supervision and follow your school's lab rules.
Willem Kolff built an early dialysis machine in the 1940s, and went on to save lives by applying physical principles to kidney failure.
Dialysis and transplants are not available to all who need them. Consider which kinds of knowledge should inform these decisions.
Summarised in our own words. Use each code to find the exact wording in your textbook or the IB subject guide.
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