Chapter 12

Compare and contrast insect Malpighian tubules and mammalian nephrons. In doing so, describe all tubular transport processes that are linked to the basolateral \(\mathrm{Na}^{+} / \mathrm{K}^{+}\)ATPase in nephrons and the V-ATPase in Malpighian tubules.

The Gulf toadfish Opsanus beto (p. 561) switches from ammonotely to ureotely when crowded or confined, releasing urea in pulses. Hypothesize why it might do this.

Explain tubular maximum \(\left(T_{m}\right)\) and renal threshold. Compare two substances that display a \(T_{\mathrm{m}}\) : one substance that is and one that is not regulated by the kidneys.

If the urine concentration of a substance is \(7.5 \mathrm{mg} / \mathrm{mL}\) of urine, its plasma concentration is \(0.2 \mathrm{mg} / \mathrm{mL}\) of plasma, and the urine flow rate is \(2 \mathrm{~mL} / \mathrm{min}\), what is the clearance rate of the substance? Is the substance being reabsorbed or secreted by the kidneys?

If the plasma concentration of substance \(X\) is \(200 \mathrm{mg} / 100 \mathrm{~mL}\) and the GFR is \(125 \mathrm{~mL} / \mathrm{min}\), what is the filtered load of this substance? If the \(T_{\mathrm{m}}\) for substance \(\mathrm{X}\) is \(200 \mathrm{mg} / \mathrm{min}\), how much of the substance will be reabsorbed at a plasma concentration of \(200 \mathrm{mg} / 100 \mathrm{~mL}\) and a GFR of \(125 \mathrm{~mL} / \mathrm{min}\) ? How much of substance \(X\) will be excreted?

Conn's syndrome is an endocrine disorder in some older domestic cats brought about by excessive growth of the adrenal cortex (sometimes due to a tumor). The result is secretion of unregulated excessive aldosterone. Given what you know about the functions of aldosterone, describe what the most prominent features of this condition would be.