#Mcat practice test princeton review series#
The most abundant radioactive nuclide on earth is 238U, which undergoes a series of decays ending in 206Pb, a stable isotope of lead. Humans are exposed to radiation from naturally-occurring radioactive elements. Neither supports nor weakens the hypothesis due to the differential effect of hormones on differing tissues. Weakens the hypothesis due to the lack of impact of leptin on renal sympathetic nerve activity.ĭ. Weakens the hypothesis due to the increase in neural activity with injection of leptin in obese miceĬ. Supports the hypothesis due to the increase in neural activity with injection of leptin in obese miceī. What impact do the results shown in Figure 1 have on the hypothesis that leptin resistance secondary to obesity reduces all effects of leptin?Ī. This research suggests that leptin resistance in obese individuals may be a selective phenomenon in the sense that not all functions of the hormone are affected by leptin resistance. No significant difference in RSNA activity was detected between lean and obese mice as depicted in Figure 1. Both groups showed an enhancement of renal sympathetic activity correlating to the increased leptin injection.
Surgery was performed to expose the appropriate nerve fascicles near the kidney and platinum electrodes recorded the multi-fiber renal SNA (RSNA) in anesthetized mice. In order to test whether leptin resistance in obese participants affected all functions of leptin, an experiment was performed in which yellow obese agouti mice and normal lean mice were injected intravenously with three different leptin concentrations while renal sympathetic nerve activity (renal SNA) was measured.
While it has been shown that leptin can activate the sympathetic nervous system, the most classic characteristic of leptin resistance is a decrease in the sense of satiety after feeding. Given the dramatic increase in nerve activity with increasing leptin dosage, leptin does have an impact on RSNA (choice C is wrong).
#Mcat practice test princeton review full#
As mentioned above, leptin resistance is primarily associated with mitigating a sense of satiety when full it is not clear whether an increase in renal sympathetic activity should be included within the leptin resistance syndrome (answer choice B is wrong). The lack of difference between RSNA in lean and obese mice is not supportive of the hypothesis that leptin resistance inhibits leptin function (answer choice A is wrong). Therefore the lack of a significant difference between obese and lean mice does not provide significant evidence to strengthen or weaken the leptin resistance hypothesis (choice D is correct). In the passage, the leptin resistance hypothesis specifically relates to satiety and, while it is known that leptin activates the sympathetic nervous system, it is unclear how renal sympathetic nerve activity (RSNA) is related to the sensation of satiety. While this may seem to contradict the leptin resistance hypothesis, leptin is a hormone which will be expected to affect target tissues differently.
The passage states that no significant difference is observed between the obese and lean mice. The slope of Figure 2 is the rate of lipid hydrolysis (change in concentration over a change in time), and as the slope with DOPC + 5 mol% of raclopride is constant, choice D is incorrect. While a higher concentration of raclopride may increase the rate of lipid hydrolysis, there is no data in Figure 2 to support this statement, and as the raclopride-H+ is regenerated in the mechanism, there is no guarantee that increasing its overall concentration leads to a greater rate (eliminate choice B). Figure 2 does show that the rate of background lipid hydrolysis is comparatively much slower than raclopride-mediated lipid hydrolysis (choice C is correct). While the data show that the rate of lipid hydrolysis is appreciable in the presence of raclopride and negligible in its absence, as raclopride acts a simple Brønsted acid, it would be incorrect to say that this exact molecule is required for any kind of lipid hydrolysis (eliminate A). Figure 2 shows the rate of lipid hydrolysis of the lipid DOPC in the presence and absence of raclopride by measuring the concentration of the hydrolyzed lipid, lyso-PC, over time.
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