Theory question 104
Excretion(a) List three functions of the kidney
(b) Make a labelled diagram of the mammalian kidney tubule (nephron)
(c) Describe how the kidney carries out two of the functions listed in "a".
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(a) Any three: excretion of nitrogenous waste (urea); osmoregulation (water balance); regulation of salts/ions; regulation of blood pH; removal of drugs/toxins
(b) Diagram labels: afferent and efferent arterioles, glomerulus, Bowman's capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting duct, capillary network
(c) Excretion: high pressure in the glomerulus forces water, urea, salts and glucose into Bowman's capsule (ultrafiltration); useful substances (glucose, most water and salts) are reabsorbed in the tubules; urea stays in the urine
Osmoregulation: when the body is short of water the pituitary releases ADH; ADH makes the distal tubule and collecting duct reabsorb more water, so urine is small and concentrated; with excess water, less ADH, so more dilute urine
Describe ultrafiltration and selective reabsorption as two separate steps.